**9. Conclusion**

In Jordan, goat production is an integral part of farming systems and plays a significant role for the food security, socioeconomic, and cultural needs of rural households. In the country, goats are valued mainly for meat, and less for milk, skins, and hair. Favoring goat keeping in these regions is attributed to the ease of rearing and efficiency of low‐quality roughage utiliza‐ tion. Due to their unique biological and physiological abilities, they can be raised successfully in zones with poor grass vegetation.

[7] Jaber L, Chedid M, Hamadeh S. Water Stress in Small Ruminants. In: Sener A, editor. Responses of Organisms to Water Stress. Croatia: InTech Open Science; 2013. pp. 115‐150

Goat Farming and Breeding in Jordan http://dx.doi.org/10.5772/intechopen.69015 379

[8] Zaitoun IS, Tabbaa MJ, Bdour S. Differentiation of native goats breeds of Jordan on the basis of morphostructural characteristics. Small Ruminant Research. 2005;**56**:173‐182 [9] Abu‐Zanat MM, Migdady HA, Tabbaa MJ. Production systems of small ruminants in

[10] Tabbaa JM, Al‐Atiyat R. Breeding objectives, selection criteria and factors influencing

[11] Sawalha R. Some genetic and non‐genetic factors affecting body dimensions of damas‐ cus kids in Jordan. [thesis]. Amma, Jordan: University of Jordan; 1998. p. 110

[12] Department of Statistics. Statistics by Sector, Agriculture, Surveys, Agriculture Surveys. Number and Characteristics of Livestock. [Internet]. 2015. Available from:http://web. dos.gov.jo/sectors/economic/agriculture/agriculture‐surveys/ [Accessed: March 2, 2017]

[13] Al‐Khaza'leh J, Reiber C, Ogutu JO, Valle Zárate A. Goat breeds performance under dif‐ ferent farming systems and conditions of water availability in the Karak Governorate,

[14] Zaitoun IS, Tabbaa MJ, Bdour S. Body weight, milk production and lifetime twinning rate of the different goat breeds of Jordan. Dirasat: Agricultural Sciences. 2004;**31**:143‐149

[15] Abu‐Zanat MM, Tabbaa MJ. Effect of drought on feed resources and performance of small ruminants in the northern Badia of Jordan. Dirasat: Agricultural Sciences.

[16] Degen AA. Sheep and goat milk in pastoral societies. Small Ruminant Research. 2007;**68**:

[17] Talafha AQ, Ababneh MM. Awassi sheep reproduction and milk production: Review.

[18] Güney OO, Torun O, Özuyank O, Darcan N. Milk production, reproductive and growth performances of Damascus goats under northern Cyprus conditions. Small Ruminant

[19] Husein MQ, Ababneh MM, Haddad SG. The effects of progesterone priming on repro‐ ductive performance of GnRH‐PGF2alpha‐treated anestrous goats. Reproduction Nutri‐

[20] Al‐Khaza'leh J, Reiber C, Al Baqain R, Valle Zárate A. A comparative economic analysis of goat production systems in Jordan with an emphasis on water use. Livestock Research for Rural Development. 2015;**27**(5). Available from: http://www.lrrd.org/lrrd27/5/

[21] Aldomy F, Hussein NO, Sawalha L, Khatatbeh K, Aldomy A. A national survey of peri‐ natal mortality in sheep and goats in Jordan. Pakistan Veterinary Journal. 2009;**29**:102‐106

middle Badia of Jordan. Dirasat‐Agricultural Sciences. 2005;**32**:205‐214

them for goat breeds in Jordan. Small Ruminant Research. 2009;**84**:8‐15

Jordan. Jordan Journal of Agricultural Sciences. 2016;**12**:441‐458

Tropical Animal Health and Production. 2011;**43**:1319‐1326

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khaz27081.html/[Accessed: June 7, 2017]

7‐19

Different Jordanian goat breeds have been identified and characterized under different pro‐ duction systems. Damascus (Shami), Mountain Black, Dhaiwi (Bedouin goat), and Desert goats are the main Jordanian goat breeds.

Goat production systems in Jordan changed gradually and shifted from extensive production to systems that involve cropping of arable land. There are several constraints limiting goat production in Jordan. Feed, disease, and drinking water shortages are some of them.


*Article* **Research on Tensile Properties of Carbon Fiber Composite Laminates**

**Jiayi Wang 1 , Lifeng Chen 2 , Wei Shen 2 and Lvtao Zhu 1,2,3,\***

**Abstract:** In order to study the thread tensile performance of carbon fiber composite laminates, the connection between the test piece, connecting bolts, bushings, and the composite matrix, was leveraged for loading, and combined with an ultra-sound scanning imaging system, experiments were carried out on the dynamic response to record the failure behavior of the laminate structure of equal thickness. The effects of different pull-off loading strengths on the dynamic failure process, deformation profile, midpoint deformation, failure mode, and energy dissipation ratio of the thread were studied. The results show that (1) with the increase in pull-off strength, the response speed of mid-point deformation increases, the thread deformation mode changes from overall deformation to partial deformation, and the localized effect increases, accompanied by severe matrix and fiber fracture failure; (2) the thread energy dissipation ratio ascends with increasing pull-off strength and exhibits three distinct stages, i.e., elastic deformation, central fracture, and complete failure, which are directly related to the structural failure mode; (3) the failure load increases with the increment of the thickness of the laminate, and the maximum failure surface of the specimen will move from the upper layer of the laminate to the lower layer along the thickness direction; (4) the deformation velocity of the midpoint augments with the increase in the tensile rate, which can be included as a factor to assess the tensile properties of carbon fiber composites.

**Keywords:** carbon fiber composite; tensile strength; laminate; tensile property

### **1. Introduction**

Carbon fiber reinforced polymer (CERP), with its high specific strength, tailored modulus, and sound stealth absorbing performance, has replaced some traditional metal materials and material structures. As an indispensable assembly of the modern aviation industry [1], carbon fiber and its composite materials represent significant advantages with regard to fatigue resistance, tensile resistance, vibration damping, volatile temperature resistance, and corrosion resistance. However, the composite structures also have some defects and are easily damaged under long-term loading, machining, and corrosion due to factors such as production process, design scheme, and retention environment. In order to effectively prevent secondary accidents, including internal and external structural damage, it is necessary to carry out real-time quality and safety inspections when they are put into use to ensure mechanical integrity and production safety.

The early research work on the dynamic failure behavior of fiber reinforced composite laminates is mainly based on the contact tensile loading formed by the drop weight impact and the penetration of the projectile. The research [2] results show that the main failure modes of fiber reinforced composite laminates include matrix and fiber fracture, spalling, and so on. Schiffer et al. [3] used an underwater tensile loading simulation device to explore the response of laminates under high-strength underwater tensile loads and established

**Citation:** Wang, J.; Chen, L.; Shen, W.; Zhu, L. Research on Tensile Properties of Carbon Fiber Composite Laminates. *Polymers* **2022**, *14*, 2318. https://doi.org/10.3390/ polym14122318

Academic Editors: Yang Zhou and Zhaoling Li

Received: 7 May 2022 Accepted: 30 May 2022 Published: 8 June 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

a theoretical analysis model for the dynamic response of composite laminates. Yang et al. [4] leveraged three-dimensional DIC to mine the transverse dynamic response process of carbon fiber woven laminates under projectile penetration.

Rajput et al. [5] studied the impact of laminate thickness on the impact response and damage mechanism through experiments and numerical analysis, and the results showed that the depth of pits had a bilinear response to the strength exerted. Karalis, G [6] studied the dynamic behavior and failure mechanism of laminates under underwater tensile loads. Lin et al. [7] conducted a comparative analysis of the dynamic failure behavior of flat and curved panel structures of woven basalt/epoxy laminates under blast loading, emphasizing the important influence of structural curvature on the dynamic response. Wei et al. [8] carried out experiments and numerical simulations on the high-speed penetration of laminates and concluded that, in addition to fiber failure, laminates under penetration loads also include spalling and matrix cracking. Penetration velocity, penetration angle, fiber layup, and laminate structure form generate rich research results on the dynamic behavior and failure of laminate structures under tensile loads [9]. Based on the Hashin failure criterion, Wang Danyong [10] and Su Rui [11] established a progressive damage analysis model for composite materials with similar ideas and also provided a life calculation result that was close to the experiment. Saeedifar et al., and Yang [12,13] established the finite element model of interlaminar fracture toughness test of fiber reinforced composites based on integral and VCCT technology, respectively, to study the delamination processes, such as crack generation and crack propagation, and the energy release rate during interlaminar failure. Three-point bending tests with complex failure forms are rarely studied, and the simulation is not accurate. Camanho [14] proposed that the initial damage inside the composite structure was mainly caused by the separation between fiber layers. Combining with the maximum stress theory, and based on the three-dimensional progressive failure constitutive model, Pearce [15] explored the stiffness degradation characteristics of composite connection structures under out-of-plane loads.

Pravalika and Kashi Ishikawa [16] studied the strength of composite joints through experiments and divided the failure types of carbon fiber composite into four types, namely fiber failure, matrix failure, interlaminar delamination, and normal shear failure, using ultrasonic scanning imaging system and observing the internal damage of the composite material. Based on the observation results, the damage process of the specimen was divided into four stages, namely the appearance of damage, the extension of local cracks, the expansion of damage, and the appearance of structural cracks. Ostapiuk and Orifici [17,18] studied the effect of the ratio of aperture to plate thickness on the connection performance. The results show that when the ratio of aperture to plate thickness is equal to 1, the bearing capacity of the composite plate is the strongest. MA Mc Patel [19] and Whitworth [20] analyzed the stress of single-nail and multi-nail connections by means of tests. The test results show that as the number of nail holes in the laminate increases, the strength of the laminate decreases. Ang [21] combined the failure criterion and the maximum stress criterion proposed by Hashin to study the mechanical connection characteristics of composite materials through experimental research and numerical simulation and predicted the strength and failure process. Zhou [22] and Zhang [23] pointed out that the pull-off failure mode is the same as the internal failure characteristics caused by low-speed stretching, mainly manifested as matrix failure and delamination; the damage extends from the edge of the hole to the surrounding area, and the damage area is distributed in a network along the thickness direction.

It can be derived from the above statement that the process of pull-off failure is very complex, and there are many factors affecting the pull-off strength of laminates, such as temperature and humidity conditions, ply ratio, material geometric parameters and constraints, etc. Due to many other reasons, there are relatively few studies on the pull-off characteristics of composite materials, and there are still many problems that need to be further explored.

This work aims at the dynamic response and failure mode of the carbon fiber composite laminates under the tensile load generated in the thread pull-off. Along with the ultrasonic characteristic scanning imaging system, the damaged specimens are tested. The pull-off test of composite laminates is carried out to obtain the pull-off strength; the load–displacement curve of the entire pull-off behavior is recorded; the layer-based damage are studied; the failure processes and the mechanical response of the laminate are analyzed. The numerical simulation results are to be further explored, focusing on the main failure modes of the laminates, i.e., the initiation and expansion of damage in the laminate layers, and their effects on the pull-off strength of the composite laminates. posite laminates under the tensile load generated in the thread pull-off. Along with the ultrasonic characteristic scanning imaging system, the damaged specimens are tested. The pull-off test of composite laminates is carried out to obtain the pull-off strength; the load– displacement curve of the entire pull-off behavior is recorded; the layer-based damage are studied; the failure processes and the mechanical response of the laminate are analyzed. The numerical simulation results are to be further explored, focusing on the main failure modes of the laminates, i.e., the initiation and expansion of damage in the laminate layers, and their effects on the pull-off strength of the composite laminates. **2. Experiments**

This work aims at the dynamic response and failure mode of the carbon fiber com-

*Polymers* **2022**, *14*, x FOR PEER REVIEW 3 of 14

### **2. Experiments**

#### *2.1. Experimental Materials 2.1. Experimental Materials*

The carbon fiber composite laminate used in this study is the T700 carbon fiber composite single-layer board. The material properties of the T700 carbon fiber composite single-layer panels are as follows: longitudinal stiffness *E*1 = 100 GPa transverse stiffness *E*2 = 80 GPa, Poisson's ratio *ν*12 = 0.21, shear modulus *G*12 = 4 GPa, longitudinal tensile strength *XT* = 2100 MPa, longitudinal compressive strength *XC* = 700 MPa, transverse tensile strength *YT* = 42 MPa, transverse compressive strength *YC* = 160 MPa, interlaminar shear strength *S* = 104 MPa, density *ρ* = 1500 kg/m3 . The carbon fiber composite laminate used in this study is the T700 carbon fiber composite single-layer board. The material properties of the T700 carbon fiber composite single-layer panels are as follows: longitudinal stiffness 100 a *E*1 = *GP* transverse stiffness 80 Pa *E*2 = *G* , Poisson's ratio ν 12 = 0.21 , shear modulus 4 Pa *G*12 = *G* , longitudinal tensile strength *X* 2100*M*Pa *T* = , longitudinal compressive strength *X* 700*M*Pa *C* = , transverse tensile strength *Y* 42*M*Pa *T* = , transverse compressive strength *Y* 160*M*Pa *C* = , interlaminar shear strength *S* =104*M*Pa , density 3 ρ=1500*kg* / *m* .

The thread pull-off (rear joint) used in this study adopts high-temperature T700 spreading cloth to form the RS03A composite material rear joint according to the requirements specified in the task book. The rear joint of the RS03A composite material is selected for the thread pull-off test. The composite material layer (matrix) and the bushing are composed of TC4 material and equipped with a boss at the bottom to bear the axial load of the bushing. The measured axial tensile properties and stress–strain curves are shown in Figure 1 and Table 1. The thread pull-off (rear joint) used in this study adopts high-temperature T700 spreading cloth to form the RS03A composite material rear joint according to the requirements specified in the task book. The rear joint of the RS03A composite material is selected for the thread pull-off test. The composite material layer (matrix) and the bushing are composed of TC4 material and equipped with a boss at the bottom to bear the axial load of the bushing. The measured axial tensile properties and stress–strain curves are shown in Figure 1 and Table 1.

**Figure 1.** Thread axial tensile stress–strain curve. **Figure 1.** Thread axial tensile stress–strain curve.

Dispersion coefficient 3.50 3.52 Note: "#"stands for nothing here. It is a symbol marked on the sample part to tell one digit apart from another.

Note: "#"stands for nothing here. It is a symbol marked on the sample part to tell one digit apart from another. Figure 1 illustrates that under the action of the axial tensile load, the stress and strain of the threaded specimen result in a smooth linear relationship. No fracture signs occur in the figure. According to the measured stress–strain curve, the axial tensile fracture strain is about 0.9%. It can be seen from Table 1 that the average axial tensile fracture strength of the thread is 1565 MPa, and the average modulus is 170.5 GPa.

### *2.2. Experiment Equipment*

*Polymers* **2022**, *14*, x FOR PEER REVIEW 4 of 14

of the thread is 1565MPa, and the average modulus is 170.5GPa.

the requirements of the task book for loading accuracy.

The test piece and the adapter are connected and tightened by bolts; the adapter is connected with the slider, and then, the adapter is inserted into the indenter. The abovementioned overall structures are placed on the inclined blank component fixed on the load-bearing ground rail, and the actuator is connected with the slider through a multistrand wire rope, as shown in Figure 2. The loading control equipment for the pull-off and bending test of the laminate test piece adopt a multi-channel coordinated loading control system. The error of the coordinated loading control system is less than 1%, which met the requirements of the task book for loading accuracy. *2.2. Experiment Equipment*  The test piece and the adapter are connected and tightened by bolts; the adapter is connected with the slider, and then, the adapter is inserted into the indenter. The abovementioned overall structures are placed on the inclined blank component fixed on the load-bearing ground rail, and the actuator is connected with the slider through a multistrand wire rope, as shown in Figure 2. The loading control equipment for the pull-off and bending test of the laminate test piece adopt a multi-channel coordinated loading control system. The error of the coordinated loading control system is less than 1%, which met

Figure 1 illustrates that under the action of the axial tensile load, the stress and strain of the threaded specimen result in a smooth linear relationship. No fracture signs occur in the figure. According to the measured stress–strain curve, the axial tensile fracture strain is about 0.9%. It can be seen from Table 1 that the average axial tensile fracture strength

**Figure 2.** Overall condition after pull-off test installation**. Figure 2.** Overall condition after pull-off test installation.

#### *2.3. Experimental Installment 2.3. Experimental Installment*

**3. Process**

*3.1. Test Process*

*3.2. Test Status*

are well performed.

During the experiment, the INSTRON1346 electro-hydraulic servo-controlled material testing machine was used to carry out tensile experiments and laminate compression experiments, as shown in Figure 2 and Figure 3. The data acquired in real time during the loading process of the test system include load, displacement, and transverse deflection. Two billets are installed at the appropriate position below the actuator with anchor bolts. The combination of the pull-head adapter and the test part is placed in the pressure head During the experiment, the INSTRON1346 electro-hydraulic servo-controlled material testing machine was used to carry out tensile experiments and laminate compression experiments, as shown in Figures 2 and 3. The data acquired in real time during the loading process of the test system include load, displacement, and transverse deflection. Two billets are installed at the appropriate position below the actuator with anchor bolts. The combination of the pull-head adapter and the test part is placed in the pressure head and placed in the center. *Polymers* **2022**, *14*, x FOR PEER REVIEW 5 of 14

displacement (test parts are required to be close to the fixture) are set to zero. Different load intensities are exerted to monitor the displacement. During the tensile process, the initial failure load, maximum load, and corresponding displacement are recorded with

The ultimate tensile strength is the maximum tensile stress that carbon fiber compo-

*bh P*

*bh l Pl E*

imen width*b* , the specimen thickness *h* , the tensile modulus *Et* . The maximum of the displacement load of the tensile test is shown in Figure 4. The test data of each group of test pieces are calculated to obtain an average tensile strength of the laminate of 783.23MPa, an average limit load of 41.97KN, and an average Poisson's ratio of 0.317, as shown in Table 2. The tensile strength, tensile elastic modulus, and Poisson's ratio data obtained from the sample are similar, which shows that the heterogeneity of the carbon fiber composite sample is within the experimental error range. The obtained test results

Δ Δ

σ

max

= (1)

1 = (2)

*t* , the maximum load *P*max , the spec-

*t*

σ

**Figure 3.** Schematic diagram of the installation of the thread pull-off test piece. **Figure 3.** Schematic diagram of the installation of the thread pull-off test piece.

sites can withstand before reaching failure under the tensile test load.

displacement control until the specimen is fractured.

Tensile strength calculation formula

Tensile modulus calculation formula

In the formula, the ultimate tensile strength is

### **3. Process**

### *3.1. Test Process*

Before starting the test, a static load spectrum is created. The loading system and displacement (test parts are required to be close to the fixture) are set to zero. Different load intensities are exerted to monitor the displacement. During the tensile process, the initial failure load, maximum load, and corresponding displacement are recorded with displacement control until the specimen is fractured.

### *3.2. Test Status*

The ultimate tensile strength is the maximum tensile stress that carbon fiber composites can withstand before reaching failure under the tensile test load.

Tensile strength calculation formula

$$
\sigma\_l = \frac{P\_{\text{max}}}{bh} \tag{1}
$$

Tensile modulus calculation formula

$$E\_1 = \frac{\Delta P l}{bh\Delta l} \tag{2}$$

In the formula, the ultimate tensile strength is *σt* , the maximum load *P*max, the specimen width *b*, the specimen thickness *h*, the tensile modulus *Et* . The maximum of the displacement load of the tensile test is shown in Figure 4. The test data of each group of test pieces are calculated to obtain an average tensile strength of the laminate of 783.23 MPa, an average limit load of 41.97 KN, and an average Poisson's ratio of 0.317, as shown in Table 2. The tensile strength, tensile elastic modulus, and Poisson's ratio data obtained from the sample are similar, which shows that the heterogeneity of the carbon fiber composite sample is within the experimental error range. The obtained test results are well performed. *Polymers* **2022**, *14*, x FOR PEER REVIEW 6 of 14

**Figure 4.** Limit load–displacement curve. **Figure 4.** Limit load–displacement curve.

### **Table 2.** Laminate tensile test results data.

from another.

In the formula:

**Table 3.** Test results.

*3.3. Finite Element Model*

2# 884.90 43.59 Note: "#"stands for nothing here. It is a symbol marked on the sample part to tell one digit apart from another.

> 3# 743.46 41.21 4# 690.16 40.08

Note: "#"stands for nothing here. It is a symbol marked on the sample part to tell one digit apart

3 / 2 )

/ 4 ) 3 3

Shown in the Equation (4) is the calculation of the flexural modulus of elasticity. *E*f

**Sample Bending strength/MPa Flexural modulus of elasticity/GPa**

Three - dimensional finite model is constructed to analyze the laminate, as shown in

Figure 5. The element type adopts the eight-node reduction integral solid element C3D8R, and the orientation of lamination is realized through material orientation. When the load is applied, the left end of the model is fixed, and the right end is applied with axial displacement load. Different strain rate conditions are realized by adjusting the step length

is the flexural modulus of elasticity, MPa; Δ*P* is the load increment of the initial straightline segment on the load-deflection curve, N;Δf is the corresponding deflection increment,

2

f is the bending strength, MPa; *P* is the maximum load value when

= *PL*( *bh* (3)

f *E* = Δ*PL* ( *bh* Δ*f* (4)

According to the literature [24,25], the bending strength can be expressed as

f σ

the sample fails, N; *L* is the span, mm; *h* is the thickness of the sample, mm.

mm, at the midpoint of the sample span. The test results are shown in Table 3.

1# 1068 162 2# 1053 137 3# 995 155 4# 989 131

σ

The flexural modulus of elasticity is

According to the literature [24,25], the bending strength can be expressed as

$$
\sigma\_{\rm f} = 3PL / \left(2bh^2\right) \tag{3}
$$

In the formula: *σ*f is the bending strength, MPa; *P* is the maximum load value when the sample fails, N; *L* is the span, mm; *h* is the thickness of the sample, mm. The flexural modulus of elasticity is

$$E\_{\rm f} = \Delta P L^3 / \left(4bh^3 \Delta f\right) \tag{4}$$

Shown in the Equation (4) is the calculation of the flexural modulus of elasticity. *E*f is the flexural modulus of elasticity, MPa; ∆*P* is the load increment of the initial straight-line segment on the load-deflection curve, N; ∆f is the corresponding deflection increment, mm, at the midpoint of the sample span. The test results are shown in Table 3.

**Table 3.** Test results.

### *3.3. Finite Element Model Polymers* **2022**, *14*, x FOR PEER REVIEW 7 of 14

Three-dimensional finite model is constructed to analyze the laminate, as shown in Figure 5. The element type adopts the eight-node reduction integral solid element C3D8R, and the orientation of lamination is realized through material orientation. When the load is applied, the left end of the model is fixed, and the right end is applied with axial displacement load. Different strain rate conditions are realized by adjusting the step length of the analysis. The time domain is set as 0.05 to simulate the quasi-static loading mode of force in the pull test. of the analysis. The time domain is set as 0.05 to simulate the quasi-static loading mode of force in the pull test.

**Figure 5.** Finite element model of composite laminate assembly.

### **Figure 5.** Finite element model of composite laminate assembly. *3.4. Damage Monitoring*

countersunk hole surface).

*3.4. Damage Monitoring*  As the composite laminate is damaged by pulling, the failure mode of the hole edge is fuzzy, and the vidual defects are not very distinct from each other. Therefore, it needs to be observed by non-destructive testing equipment. In this test, the ultrasonic characteristic scanning imaging system (UTF-SCAN -1 Water immersion C-scan detection system) performs non-destructive testing on the damaged specimens. The location, size, and dam-As the composite laminate is damaged by pulling, the failure mode of the hole edge is fuzzy, and the vidual defects are not very distinct from each other. Therefore, it needs to be observed by non-destructive testing equipment. In this test, the ultrasonic characteristic scanning imaging system (UTF-SCAN-1 Water immersion C-scan detection system) performs non-destructive testing on the damaged specimens. The location, size, and damage plan of the damaged area of the laminate can be obtained by ultrasonic C-scanning. The Cscan non-destructive testing test is carried out on the test pieces of different thicknesses after the pull-off test, and the damage of each layer of the test pieces with different thicknesses,

(**a**) (**b**) (**c**)

fourth layer, 1.25 mm, (**b**) the ninth layer, 3.25 mm, (**c**) the seventh layer, 5.10 mm.

**Figure 6.** The maximum failure surface and depth of the specimen with different thickness: (**a**) the

age plan of the damaged area of the laminate can be obtained by ultrasonic C-scanning.

nesses after the pull-off test, and the damage of each layer of the test pieces with different thicknesses, area, and depth is obtained. As shown in Figure 6 (a, b, c) above, the maximum failure surface of the specimen with a thickness of 1.25 mm is located in the lower layer of the laminate, that is, the fourth layer (90-degree direction), and the specimen with a thickness of 3.25 mm has the largest failure surface, while the failure surface is located in the middle layer of the laminate, that is, the ninth layer (90-degree direction). The maximum failure surface of the specimen with a thickness of 5.10 mm is located in the upper layer of the laminate, that is, the seventh layer (0-degree direction). It can be seen that with the increase in the thickness of the specimen, the position of the maximum failure surface of the specimen moves along the thickness direction from the upper layer position (including the straight hole surface) of the laminate to the lower layer position (including the

area, and depth is obtained. As shown in Figure 6a–c above, the maximum failure surface of the specimen with a thickness of 1.25 mm is located in the lower layer of the laminate, that is, the fourth layer (90-degree direction), and the specimen with a thickness of 3.25 mm has the largest failure surface, while the failure surface is located in the middle layer of the laminate, that is, the ninth layer (90-degree direction). The maximum failure surface of the specimen with a thickness of 5.10 mm is located in the upper layer of the laminate, that is, the seventh layer (0-degree direction). It can be seen that with the increase in the thickness of the specimen, the position of the maximum failure surface of the specimen moves along the thickness direction from the upper layer position (including the straight hole surface) of the laminate to the lower layer position (including the countersunk hole surface). thicknesses, area, and depth is obtained. As shown in Figure 6 (a, b, c) above, the maximum failure surface of the specimen with a thickness of 1.25 mm is located in the lower layer of the laminate, that is, the fourth layer (90-degree direction), and the specimen with a thickness of 3.25 mm has the largest failure surface, while the failure surface is located in the middle layer of the laminate, that is, the ninth layer (90-degree direction). The maximum failure surface of the specimen with a thickness of 5.10 mm is located in the upper layer of the laminate, that is, the seventh layer (0-degree direction). It can be seen that with the increase in the thickness of the specimen, the position of the maximum failure surface of the specimen moves along the thickness direction from the upper layer position (including the straight hole surface) of the laminate to the lower layer position (including the countersunk hole surface).

As the composite laminate is damaged by pulling, the failure mode of the hole edge is fuzzy, and the vidual defects are not very distinct from each other. Therefore, it needs to be observed by non-destructive testing equipment. In this test, the ultrasonic characteristic scanning imaging system (UTF-SCAN -1 Water immersion C-scan detection system) performs non-destructive testing on the damaged specimens. The location, size, and damage plan of the damaged area of the laminate can be obtained by ultrasonic C-scanning. The C-scan non-destructive testing test is carried out on the test pieces of different thicknesses after the pull-off test, and the damage of each layer of the test pieces with different

*Polymers* **2022**, *14*, x FOR PEER REVIEW 7 of 14

**Figure 5.** Finite element model of composite laminate assembly.

force in the pull test.

*3.4. Damage Monitoring*

of the analysis. The time domain is set as 0.05 to simulate the quasi-static loading mode of

(**a**) (**b**) (**c**)

**Figure 6.** The maximum failure surface and depth of the specimen with different thickness: (**a**) the fourth layer, 1.25 mm, (**b**) the ninth layer, 3.25 mm, (**c**) the seventh layer, 5.10 mm. **Figure 6.** The maximum failure surface and depth of the specimen with different thickness: (**a**) the fourth layer, 1.25 mm, (**b**) the ninth layer, 3.25 mm, (**c**) the seventh layer, 5.10 mm.

### **4. Results and Discussion**

### *4.1. Analysis of Tensile Properties of Carbon Fiber Composites*

After, respectively, exploring the axial tensile properties of composite materials and threaded composite materials, the rear joint of RS03A composite material is selected for thread tensile testing. The load–displacement curve during the tensile process is shown in Figure 7. As can be seen from Figure 7, when the load is applied to a certain level (point A in Figure 7), it will suddenly drop, and the composite material will emit a crisp sound during the experiment; the load at this time is defined as the initial failure load [26]. As the displacement increases, the load continues to increment, and the sound continues to appear during the period until the last loud sound. The cylinder composite material breaks as a whole, and the maximum load at this time is the breaking load. The initial failure load and fracture load are used to calculate the stresses, which are recorded as the initial failure stress (*σ*1) and the final failure stress (*σ*2).

At the beginning of the experiment, the appearance of the laminate basically does not change, and the stress–strain curve shows a linear rise. When the strain reaches 4500 *µε*, the edge of the hole in contact between the laminate and the adapter begins to have a small fiber uplift, and there is a clear and crisp squeak, indicating that the laminate begins to damage. As the displacement continues to increase, the area of the uplifted fiber increases slowly, and the damage range expands from the center of the circular hole to the edge of the laminate, and some fibers are pulled off at the edge of the hole. The load drops slightly, the curve of the increase in stress continues to rise slowly. As the load continues to drop, it is accompanied by a continuous brittle sound. Finally, the "explosion" is carried out in the "middle section" of the failure mode until the laminated plate is completely destroyed. Fiber fracture, delamination, fiber pull, and debonding are found at all locations, indicating that the matrix and interface are severely damaged during loading.

**Figure 7.** Load–displacement curve of axial tension. **Figure 7.** Load–displacement curve of axial tension.

**4. Results and Discussion**

initial failure stress (

σ

*4.1. Analysis of Tensile Properties of Carbon Fiber Composites*

After, respectively, exploring the axial tensile properties of composite materials and

σ2 ).

> με,

At the beginning of the experiment, the appearance of the laminate basically does not

change, and the stress–strain curve shows a linear rise. When the strain reaches 4500

the edge of the hole in contact between the laminate and the adapter begins to have a small fiber uplift, and there is a clear and crisp squeak, indicating that the laminate begins to damage. As the displacement continues to increase, the area of the uplifted fiber increases slowly, and the damage range expands from the center of the circular hole to the edge of the laminate, and some fibers are pulled off at the edge of the hole. The load drops slightly, the curve of the increase in stress continues to rise slowly. As the load continues to drop, it is accompanied by a continuous brittle sound. Finally, the "explosion" is carried out in the "middle section" of the failure mode until the laminated plate is completely destroyed. Fiber fracture, delamination, fiber pull, and debonding are found at all locations, indicat-

threaded composite materials, the rear joint of RS03A composite material is selected for thread tensile testing. The load–displacement curve during the tensile process is shown in Figure 7. As can be seen from Figure 7, when the load is applied to a certain level (point A in Figure 7), it will suddenly drop, and the composite material will emit a crisp sound during the experiment; the load at this time is defined as the initial failure load [26]. As the displacement increases, the load continues to increment, and the sound continues to appear during the period until the last loud sound. The cylinder composite material breaks as a whole, and the maximum load at this time is the breaking load. The initial failure load and fracture load are used to calculate the stresses, which are recorded as the

1 ) and the final failure stress (

ing that the matrix and interface are severely damaged during loading.

The stress–strain curve of axial tension is shown in Figure 8. It can be seen that the axial tensile modulus of the composite samples is relatively stable, with an average value of about 90 GPa. The average initial failure stress is about 470 MPa, and the final failure stress average is about 800 MPa. Shown in Figure 9 is the photo of the composite material after fracture. It can be seen from the figure that when the composite material is finally damaged, the fiber is fractured. At the same time, it can be seen that the fiber layer also cracks many times during the fracture. The final breaking load of the composite material is caused by the fracture of the helical fiber as the main force carrier. When the first load occurs, the hoop layer composite material has already cracked. At this time, its initial failure stress is about 470 MPa, and the axial tensile fracture strain is about 0.5%, manifesting The stress–strain curve of axial tension is shown in Figure 8. It can be seen that the axial tensile modulus of the composite samples is relatively stable, with an average value of about 90 GPa. The average initial failure stress is about 470 MPa, and the final failure stress average is about 800 MPa. Shown in Figure 9 is the photo of the composite material after fracture. It can be seen from the figure that when the composite material is finally damaged, the fiber is fractured. At the same time, it can be seen that the fiber layer also cracks many times during the fracture. The final breaking load of the composite material is caused by the fracture of the helical fiber as the main force carrier. When the first load occurs, the hoop layer composite material has already cracked. At this time, its initial failure stress is about 470 MPa, and the axial tensile fracture strain is about 0.5%, manifesting that the decrease in the first load force in value is due to the failure of the composite laminate reaching the breaking strain. In the actual working conditions of the composite material used in this experiment, if cracking occurs, it signifies a functional failure. Therefore, the initial failure stress when the load decreases for the first time is used as the criterion for judging whether the composite material fails. *Polymers* **2022**, *14*, x FOR PEER REVIEW 9 of 14 that the decrease in the first load force in value is due to the failure of the composite laminate reaching the breaking strain. In the actual working conditions of the composite material used in this experiment, if cracking occurs, it signifies a functional failure. Therefore, the initial failure stress when the load decreases for the first time is used as the criterion for judging whether the composite material fails.

The picture after fracture of composite material is shown in Figure 9. It can be seen from the

Figure 10a,b shows the interfacial delamination damage at 5%–100% loading percent-

age, respectively. The matrix cracking first appears on the back of the laminate, the damage occurs in the middle area of the laminate, and the damage area of the unit layer farther from the tensile side is larger than that near the tensile side, which can be explained by the deformation and failure principle of the laminate, that is, matrix tensile damage starts from the back and extends to the upper layer [27]. With the increase in tensile energy, the cracked area of the matrix gradually expands. The damage profile of each layer is roughly an irregular ellipse and expands along the fiber direction. This is because the stress is transmitted faster in the fiber direction, so the damage profile in the fiber direction is

larger, which is consistent with the experimental results.

picture that fiber fracture occurs when the composite material is finally destroyed. At the same time, it can be seen that the fiber layer of the fracture also occurs several times. The final fracture load of the composite is large, which is caused by the fracture of the helical fiber. The test curve shows that the tensile failure of composite laminates is divided into two stages, and it is a nonlinear and pro-

**Figure 8.** Stress–strain curve of axial tension. **Figure 8.** Stress–strain curve of axial tension.

**Figure 9.** Fracture photo.

gressive failure process.

*4.2. Layer-Based Damage*

**Figure 8.** Stress–strain curve of axial tension.

for judging whether the composite material fails.

that the decrease in the first load force in value is due to the failure of the composite laminate reaching the breaking strain. In the actual working conditions of the composite material used in this experiment, if cracking occurs, it signifies a functional failure. Therefore, the initial failure stress when the load decreases for the first time is used as the criterion

### **Figure 9.** Fracture photo.

**Figure 9.** Fracture photo. The picture after fracture of composite material is shown in Figure 9. It can be seen from the picture that fiber fracture occurs when the composite material is finally destroyed. At the same time, it can be seen that the fiber layer of the fracture also occurs several times. The final fracture load of The picture after fracture of composite material is shown in Figure 9. It can be seen from the picture that fiber fracture occurs when the composite material is finally destroyed. At the same time, it can be seen that the fiber layer of the fracture also occurs several times. The final fracture load of the composite is large, which is caused by the fracture of the helical fiber. The test curve shows that the tensile failure of composite laminates is divided into two stages, and it is a nonlinear and progressive failure process.

### the composite is large, which is caused by the fracture of the helical fiber. The test curve shows that *4.2. Layer-Based Damage*

the tensile failure of composite laminates is divided into two stages, and it is a nonlinear and progressive failure process. *4.2. Layer-Based Damage*  Figure 10a,b shows the interfacial delamination damage at 5%–100% loading percentage, respectively. The matrix cracking first appears on the back of the laminate, the damage occurs in the middle area of the laminate, and the damage area of the unit layer farther Figure 10a,b shows the interfacial delamination damage at 5–100% loading percentage, respectively. The matrix cracking first appears on the back of the laminate, the damage occurs in the middle area of the laminate, and the damage area of the unit layer farther from the tensile side is larger than that near the tensile side, which can be explained by the deformation and failure principle of the laminate, that is, matrix tensile damage starts from the back and extends to the upper layer [27]. With the increase in tensile energy, the cracked area of the matrix gradually expands. The damage profile of each layer is roughly an irregular ellipse and expands along the fiber direction. This is because the stress is transmitted faster in the fiber direction, so the damage profile in the fiber direction is larger, which is consistent with the experimental results.

from the tensile side is larger than that near the tensile side, which can be explained by the deformation and failure principle of the laminate, that is, matrix tensile damage starts from the back and extends to the upper layer [27]. With the increase in tensile energy, the cracked area of the matrix gradually expands. The damage profile of each layer is roughly an irregular ellipse and expands along the fiber direction. This is because the stress is transmitted faster in the fiber direction, so the damage profile in the fiber direction is larger, which is consistent with the experimental results. The figures indicate that delamination occurs at each interface with varying degrees of damage. When the damage variable is equal to 1, complete delamination is indicated. The main axis of the delamination area (45◦/−45◦ ) is along the −45◦ direction, and the main axis of the delamination area (−45◦/45◦ ) is along the 45◦ direction, that is, the main direction of the delamination damage is along the laying of the fibers close to the direction of the lower layer. It can also be seen that, regardless of the load percentage, the interface near the back of the tensile point is the first to experience delamination damage with the largest damage area. However, the damage variables of the other layers are between 0 and 1, which only achieves a partial delamination effect. With the same energy, the closer the sublayer to the tensile side, the smaller the degree of delamination damage. This is because when the laminate is stretched, the sublayers farther from the stretched side are subjected to greater tensile stress than the sublayers adjacent to the stretched side, so the damage propagates from the bottom layer to the top layer. Additionally, with the increase in energy, except for the bottom layer, the delamination damage area of other layers also becomes larger.

**Figure 10.** Matrix tensile damage distribution under load of different percentage: (**a**) load intensity 5 × 10−2 to 25 × 10−2, (**b**) load intensity 25 × 10−2 to 50 × 10−2, (**c**) load intensity 50 × 10−2 to 75 × 10−2, (**d**) **Figure 10.** Matrix tensile damage distribution under load of different percentage: (**a**) load intensity 5 × 10−2 to 25 × 10−2 , (**b**) load intensity 25 × 10−2 to 50 × 10−2 , (**c**) load intensity 50 × 10−2 to 75 × 10−2 , (**d**) load intensity 75 × 10−2 to 100 × 10−2 .

### load intensity 75 × 10−2 to 100 × 10−2. *4.3. Based on Mechanical Response*

The figures indicate that delamination occurs at each interface with varying degrees of damage. When the damage variable is equal to 1, complete delamination is indicated. Under the pressure of out-of-plane load, the mechanical response of the pull-out failure process of the connected structures demonstrates the following four stages.

The main axis of the delamination area (45°/−45°) is along the −45° direction, and the main axis of the delamination area (−45°/45°) is along the 45° direction, that is, the main direction of the delamination damage is along the laying of the fibers close to the direction of the lower layer. It can also be seen that, regardless of the load percentage, the interface near the back of the tensile point is the first to experience delamination damage with the The bolt stays in the pre-tightening stage, and the load is transferred through the contact pair of the model. The materials of each component are in the elastic stage, and the connecting structure experiences no macro damage. In the model, the damage variable value of the cohesive force unit increases from 0, and there is microcrack damage between material interfaces. At this stage, during the initial loading process, the load and displacement increase rapidly until the maximum load is reached.

largest damage area. However, the damage variables of the other layers are between 0 and 1, which only achieves a partial delamination effect. With the same energy, the closer the sublayer to the tensile side, the smaller the degree of delamination damage. This is because when the laminate is stretched, the sublayers farther from the stretched side are subjected to greater tensile stress than the sublayers adjacent to the stretched side, so the damage propagates from the bottom layer to the top layer. Additionally, with the increase During the plastic stage, the stiffness of the connecting structure decreases [28]. Weak plastic deformation occurs at both ends of the screw hole, the increasing rate of load slows down, and the contact pair between the bolt and the screw hole produces weak slip. At this stage, the displacement of the laminated plate continues to increase, but the bearing capacity fluctuates up and down, indicating that the matrix of the laminated plate had been damaged and can no longer bear the load, and internal damage had occurred, leading to the decline of stiffness.

in energy, except for the bottom layer, the delamination damage area of other layers also becomes larger. *4.3. Based on Mechanical Response*  Under the pressure of out-of-plane load, the mechanical response of the pull-out fail-The carbon fiber composite has anisotropic characteristics, and the pulling load is in the direction of the laminate method, with bearing performance [29]. When the load displacement is increased to about 0.58 mm, the damage variable value in the model reaches the failure limit, and the fiber layer is separated in the area near the screw hole, resulting in tension, compression, and shear failure of fiber and matrix material. When the stress

The bolt stays in the pre-tightening stage, and the load is transferred through the

the connecting structure experiences no macro damage. In the model, the damage variable value of the cohesive force unit increases from 0, and there is microcrack damage between

ure process of the connected structures demonstrates the following four stages.

of the cohesive element reaches the fracture toughness value of the interface, the adapter disconnects from the fiber layer. The internal micro-clearance of laminates and partial contact failure at the screw hole lead to the deterioration of the stiffness of the connecting structure. Figure 11 shows the fiber damage status after tensile failure. increased. When the load reaches the ultimate stress value, the metal in the ring region of the head produces crushing failure [30]. The ultimate load is the tensile strength of the connecting structure.

structure. Figure 11 shows the fiber damage status after tensile failure.

*Polymers* **2022**, *14*, x FOR PEER REVIEW 11 of 14

ment increase rapidly until the maximum load is reached.

ing to the decline of stiffness.

material interfaces. At this stage, during the initial loading process, the load and displace-

plastic deformation occurs at both ends of the screw hole, the increasing rate of load slows down, and the contact pair between the bolt and the screw hole produces weak slip. At this stage, the displacement of the laminated plate continues to increase, but the bearing capacity fluctuates up and down, indicating that the matrix of the laminated plate had been damaged and can no longer bear the load, and internal damage had occurred, lead-

During the plastic stage, the stiffness of the connecting structure decreases [28]. Weak

The carbon fiber composite has anisotropic characteristics, and the pulling load is in

Conical uplift occurs near the hole of the laminates. Due to the extrusion of the bolt

contact surface, the micro-gap inside the composite is compressed, the stiffness of the connection structure is appropriately increased, and the slope of the response curve is slightly

the direction of the laminate method, with bearing performance [29]. When the load displacement is increased to about 0.58 mm, the damage variable value in the model reaches the failure limit, and the fiber layer is separated in the area near the screw hole, resulting in tension, compression, and shear failure of fiber and matrix material. When the stress of the cohesive element reaches the fracture toughness value of the interface, the adapter disconnects from the fiber layer. The internal micro-clearance of laminates and partial contact failure at the screw hole lead to the deterioration of the stiffness of the connecting

**Figure 11.** Fiber damage status (**a**,**b**). **Figure 11.** Fiber damage status (**a**,**b**).

*4.4. Failure Mode Based*  Due to the continuous loading of the equipment, the laminate will slowly deform and fail as the loading strength of the jack increases. The central loading area of the laminate Conical uplift occurs near the hole of the laminates. Due to the extrusion of the bolt contact surface, the micro-gap inside the composite is compressed, the stiffness of the connection structure is appropriately increased, and the slope of the response curve is slightly increased. When the load reaches the ultimate stress value, the metal in the ring region of the head produces crushing failure [30]. The ultimate load is the tensile strength of the connecting structure.

#### beam is subject to the maximum stress due to bending/tensioning [31,32]. Being exposed *4.4. Failure Mode Based*

to the action of incident compressive stress waves and bending waves, the threads will form lateral deformations and localized wrinkles at the edges in contact with the laminate beams. The compressive stress wave is reflected by the backside of the laminate to form a tensile wave. When the tensile wave intensity is large enough, the laminate will undergo spalling between the fiber and the matrix. Under sufficient loading strength, with the increase in transverse deformation and axial tensile, the fracture failure of the matrix and fibers occurs in the laminate. Due to the continuous loading of the equipment, the laminate will slowly deform and fail as the loading strength of the jack increases. The central loading area of the laminate beam is subject to the maximum stress due to bending/tensioning [31,32]. Being exposed to the action of incident compressive stress waves and bending waves, the threads will form lateral deformations and localized wrinkles at the edges in contact with the laminate beams. The compressive stress wave is reflected by the backside of the laminate to form a tensile wave. When the tensile wave intensity is large enough, the laminate will undergo spalling between the fiber and the matrix. Under sufficient loading strength, with the increase in transverse deformation and axial tensile, the fracture failure of the matrix and fibers occurs in the laminate.

Figure 12 compares the deformation profile with time and strength at 50% and 100%, showing the obvious localization of deformation. When the loading strength is between 5% and 50%, and the velocity is 1.5 mm/min, the two sides of the laminate always slip along the radial direction without lateral deformation. However, when the velocity is set Figure 12 compares the deformation profile with time and strength at 50% and 100%, showing the obvious localization of deformation. When the loading strength is between 5% and 50%, and the velocity is 1.5 mm/min, the two sides of the laminate always slip along the radial direction without lateral deformation. However, when the velocity is set at 1 mm/min, the transverse defection will move sharply. When the loading percentage is 40–50%, the deformation gradually diminishes. With the increment of structural deformation, the target plate finally leaves the fixture and continues to move with a certain kinetic energy. When the loading percentage is greater than 50%, the laminate mainly undergoes elastic deformation, and no obvious failure occurs on the surface of the laminate. When the loading percentage reaches 60%, the laminate fails with the increase in tensile strength. The laminate is completely broken when the load reaches 90%.

**Figure 12.** Deformation profiles of laminates at different loading strengths and velocities. **Figure 12.** Deformation profiles of laminates at different loading strengths and velocities.

### **5. Conclusions**

**5. Conclusions**  An experimental study on tensile properties of carbon fiber composite laminates was An experimental study on tensile properties of carbon fiber composite laminates was carried out.The damage condition of the laminates' layer, the mechanical response, and failure mode were discussed.

strength. The laminate is completely broken when the load reaches 90%.

at 1 mm/min, the transverse defection will move sharply. When the loading percentage is 40%–50%, the deformation gradually diminishes. With the increment of structural deformation, the target plate finally leaves the fixture and continues to move with a certain kinetic energy. When the loading percentage is greater than 50%, the laminate mainly undergoes elastic deformation, and no obvious failure occurs on the surface of the laminate. When the loading percentage reaches 60%, the laminate fails with the increase in tensile

fracture failure of local nature, with high safety. (4) The deformation velocity of the midpoint increases with the increase in the tensile rate. When the rate and load increase simultaneously, localization failure occurs, and the critical maximum deformation of laminates decreases with the increase in the rate. Both the loading strength and tensile rate can be used as factors to assess the tensile properties **Author Contributions:** Conceptualization, J.W. and L.Z.; methodology, J.W. and L.Z.; software, J.W. and W.S.; validation, J.W.; formal analysis, J.W.; investigation, L.C.; resources, L.C. and W.S.; data curation, J.W.; writing—original draft preparation, J.W.; writing—review and editing, J.W. and L.Z.; visualization, W.S.; supervision, L.Z.; project administration, L.Z.; funding acquisition, L.Z. All authors have read and agreed to the published version of the manuscript.

of carbon fiber composites.

**Funding:** This research was funded by Zhejiang Provincial Natural Science Foundation of China (LGG21E050025), Fundamental Research Funds of Zhejiang Sci-Tech University (20202113-Y), and Fundamental Research Funds of Shaoxing Keqiao Research Institute of Zhejiang Sci-Tech University (KYY2021001G).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data sharing not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

### **References**

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www.mdpi.com

ISBN 978-3-0365-6734-1


*4.1.2 Monitoring of water and vector-borne diseases*

Many infectious diseases in the Maghreb region, especially in the aftermath of several disasters, were addressed by installing and functioning of water and sanitation facilities through many legislations which aim to save water and also save lives [37–39]. Moreover, some countries specific directives are listed below:


**4. Small-Molecule Inhibitors of NF-**κ**B in Sjögren's Syndrome**

The modulation of the NF-κB pathways has frequently been described as "pro-inflammatory", largely due to the key role of NF-κB in the pro-inflammatory genes expression including cytokines, chemokines, and adhesion molecules [42,43]. Many findings demonstrated that epithelial cells in the glandular sites of patients affected by pSS are able to release factors that address the chemoattraction of lymphocytes and promote chronic inflammatory responses [12,15,16,24–26]. NF-κB pathway modulation was therefore investigated in pSS, highlighting a role in regulating the production of pro-inflammatory cytokines, leukocyte enrolment, or cell survival [17,18,25,26,44]. In pSS, the NF-κB activation cascade can be modulated at different levels [30]. Considering the correlation with the biopsy focus score, grade of infiltration and evaluated disease activity, phosphorylated IKKε, responsible for the degradation of IkB proteins, were significantly and positively correlated with NF-κB levels in pSS [4]. The levels of B-Cell Activating Factor (BAFF) and those of numerous pro-inflammatory cytokines, all regulated by NF-κB signalling, are augmented in pSS [45]. Nucleotide polymorphisms in NF-κB pathway genes have been linked with pSS [46], and a specific mutation in the Ikα-826T, one of the promoters of a member of the inhibitory IkB complex, was associated with susceptibility of pSS [47,48]. Numerous small molecule inhibitors of the NF-κB signalling pathways are currently commercially available for use, and NF-κB modulators are under study in clinical trials for pSS treatment [19,25,30,49–54]. Many preclinical studies have already analysed the role of NF-κB signalling in the glandular tissue in pSS. The pSS SGECs have been recognized to have an active NF-κB pathway. The phosphorylated forms of IKKε, IκBα, and NF-κB were expressed in the ductal cells in minor SGs derived from pSS patients [19]. By stimulating the Toll-Like Receptor 2 (TLR2) in SGECs, IL-2 production was induced through the NF-κB cascade in pSS SGECs [49–51]. SGECs treated with the anti-Ro/SSA autoantibodies isolated from pSS patients showed a progressive increase in constitutive NF-κB activation, and transfection of SGECs with IκBα in SGECs treated with anti-Ro/SSA led to a remarkable production of pro-inflammatory cytokines and an enhanced apoptosis [25]. Furthermore, recent findings showed that gene silencing of the natural NF-κB inhibitor TNF Alpha Induced Protein 3 (TNFAIP3) in keratin-14-positive epithelial cells, promoting the activation of the constitutive NF-κB cascade, induces the initial phases of pSS, leading to a reduced production of saliva and lymphocyte invasion in the SGs [52]. This effect is likely related to the calcium pathway in the acinar cells, since calcium signalling has an important role in NF-κB pathway activity [53,54]. A list of NF-κB small molecule inhibitors tested in pSS is reported in Table 1.

**Table 1.** List of NF-κB small molecules inhibitors tested or identified in primary SS (pSS).


**3.3 Toxicokinetics**

The prevalence of organic organophosphates in living organisms has become a research target. Toxicological research has suggested that chronic exposure may be directly related to damage to the endocrine system, with a high risk of reproduction being impaired. These compounds may also be related to systemic toxicity, affecting other important organs [101].

Unintentional dust ingestion and skin absorption are the routes with the highest organic organophosphate absorption rate. How these compounds are distributed in biological tissues has not been completely elucidated. However, the highest organophosphates levels have been found in the liver, muscle, and gonads [100].

Compounds are biotransformed through metabolization to diesters and hydroxylation by phase I reactions, followed by conjugation with glucuronide and sulfate in

phase II reactions. These reactions happen both in humans and other living beings. Biotransformation products are important for monitoring and evaluating exposure to organophosphates: these products are eliminated fast because they are very hydrophilic [105].

Although organophosphate metabolism is relatively fast, even low concentrations of the metabolites may have physiological and endocrine effects. Considering that human exposure to these compounds is high and that multiple exposure pathways exist, the concern is enormous. For instance, children are generally less able to metabolize and to excrete xenobiotics, so these compounds are more toxic to them [106].

#### **3.4 Toxicological effects**

Among the potential adverse effects of organic organophosphates, reproductive and neurological effects are highlighted. Although the toxicity mechanisms of these compounds have not been fully elucidated, the consequences of being exposed to them involve cell apoptosis, ROS production, membrane disturbance, and mitochondrial alterations, among others [100].

Neurotoxic effects are concentration-dependent and inhibit DNA synthesis, decreasing the number of cells and altering neural differentiation. Acetylcholinesterase (AChE) inhibition is another reported mechanism. AChE is a widely used marker in neurotoxicity studies. Tris-(1,3-dichloro-2-propyl) phosphate (TDCPP) and TPhP have an affinity for the nervous system and are commonly associated with neurotrophic factor inhibition [107].

Aquatic organisms are often exposed to organophosphates, which tend to be neurotoxic to them. Sun et al. [108] analyzed the neurotoxicity of the halogenated tris-(2 chloroethyl) phosphate (TCEP) and the non-halogenated alkyl tri-*n*-butyl phosphate (TNBP) in zebrafish (*Dario rerio*). More specifically, these authors analyzed locomotor behavior, enzymatic activity, and AChE gene transcription. They found that zebrafish exposure to these compounds in early life stages affects locomotor behavior and gene transcription, suggesting that exposure to organophosphates may be relevant in humans, especially in children.

Exposure at developmental stages may also affect cardiac development. Cardiac development comprises several stages for increasing formation during embryogenesis. When the process occurs properly, chamber formation and maturation, septation, and valve formation take place correctly [109].

Using zebrafish as a model species for studies on developmental toxicity is advantageous and has been gaining ground in several areas of toxicology. Alzualde et al. [110] used zebrafish as a model in developmental toxicity assays to test not only the cardiotoxicity but also the neuro- and hepatotoxicity of organophosphates. These authors found that TPhP affects the heartbeat and reduces locomotor activity and hepatic edema. These data are extremely relevant when it comes to human biomonitoring.

Abe et al. [111] evaluated the toxicity of halogen-free flame retardants in zebrafish to trace a toxicity profile. At all concentrations used, ALPi did not show any sublethal or teratogenic effects, suggesting that ALPi may be a good alternative for brominated flame retardants. However, further studies are still needed to support this information [111].

The crustacean *Daphnia magna* is also a widely used model for toxicity testing. To test the chronic toxicity of ALPi, Waaijers et al. [112] exposed *D. magna* by 21 for toxicity tests. The toxicity of ALPi increased with the time of exposure, with low acute toxicity and moderate chronic toxicity [112].

TDCPP and TPhP are also potential endocrine disruptors, altering hormone levels and decreasing semen quality in adult men. Furthermore, the concentration of these compounds in house dust has been correlated with decreased sperm concentration, increased prolactin level, and decreased free thyroxin (T4) level [113].

Given that reproductive system integrity also depends on the organism's redox state, An et al. [114] tested TPhP and TCPP cytotoxicity in HepG2, A549, and Caco-2 cells. In addition to inhibiting cell viability, these compounds increase ROS production, inducing DNA damage and mitochondrial dysfunction. These changes in redox balance may harm steroidogenesis and even estrogen metabolism, being directly related to reproductive changes.

Epidemiological studies on exposure to organophosphates are also gaining ground, especially when it comes to the early stages of development, when organophosphates may have greater consequences [115].

In a cohort study, Castorina et al. [116] evaluated how exposure to organophosphates, mainly TPhP, affected the cognitive or behavioral development of 310 schoolage children. The authors monitored exposure by analyzing metabolites present in pregnant women's urine. They observed decreased intelligence quotient and working memory, associated with an increased level of the urinary metabolite diphenyl phosphate (DPhP).

Although some compounds have been widely used in research, and even though much information is available, the effects of other types of organophosphates remain to be elucidated. For example, toxicity data on BPA-DP and RDP are limited, so their consequences on human health are unknown [82].

Monitoring organic organophosphate metabolites is necessary to assess and control biological exposure, not to mention that these metabolites may play important biological roles in the toxicity of these compounds. In any case, many studies on organic organophosphates are still needed to understand their toxic effects and to reduce exposure to them [117].


**Acknowledgements**

The authors are grateful for the United Arab Emirates University (Office of the Deputy Vice Chancellor for Research & Graduate Studies) who funded this work under Fund number G00003084, 2019/2020.

#### **Appendix A**

Note that reactions R8, R8\*, R9, and R12 presented in **Table A.1** (for H2SO4) are common in all acid-leaching processes using HNO3 (**Table A.2**), HCl (**Table A.3**), and HClO4 (**Table A.4**)

#### **Table A.1.**

*Calculated ΔHR and ΔGR at 30°C for the reactions of the main SPL constituents when leached with H2SO4 solution.*

#### *Waste Material Recycling in the Circular Economy - Challenges and Developments*

*a Stands for reactions involving HF(g) or HCN(g).*

*b Stands for alternative spontaneous reaction.*

*c ΔGR at T > 100°C. d*

*ΔGR at T > 180°C.*

#### **Table A.2.**

*SPL reactions with HNO3 and their ΔHR and ΔGR at 30°C.*

#### **Table A.3.**

*SPL reactions with HCl(g) and their ΔHR and ΔGR at 30°C.*

*A Zero-Waste Process for the Treatment of Spent Potliner (SPL) Waste DOI: http://dx.doi.org/10.5772/intechopen.99055*

*Stands for reactions involving HF(g) or HCN(g).*

*b Stands for alternative spontaneous reaction.*

*c Stands for HClO4(ia). d*

*ΔGR at T > 240°C. e ΔGR at T > 225°C.*

*f*

*ΔGR at T > 550°C. g ΔGR at T > 350°C.*

#### **Table A.4.**

*SPL reactions with HClO4(g) and their ΔHR and ΔGR at 30°C.*

#### **Table A.5.**

*Calculated ΔHR and ΔGR at 30°C for other potential reactions taking place during the SPL leaching process.*


**Abstract**

This chapter describe the possibilities of MicroRNAs (miRNAs) in crop plants gene expression regulation in different metabolic pathways. Several current researches have shown different environmental stresses induce abnormal expression of miRNA, thus signifying that miRNAs may be an appropriate tool for genetical improvement in plant for stress tolerance. These miRNAs mainly control gene expression through translational inhibition. Generally, stress induce miRNAsbased inhibition of their target mRNAs, however, positive transcription factors accumulated and become more active after mRNA inhibition. Initially, researchers were mainly focused on miRNA identification, appropriate to specific or multiple environmental condition, expression profiling and recognize their roles in stress tolerance. Transformed miRNA expression studied in some plant species for better understanding of plant development and stress tolerance such as heavy metal, salinity, temperature, drought and nutrient deficiency. All these findings indicate that miRNAs act as a potential tool for genetic engineering and to enhance stress tolerance in crop plants.

**Keywords:** RNA, miRNA, siRNA, biotic and abiotic stresses, plant development


**2.1 Rigid landslide models**

In 2013, *Romano et al.* [11] carried out a 3D experiment to investigate the alongshore propagation features and the trapping mechanisms of tsunamis generated by semi-elliptical subaerial landslides around the coast of a circular island. They used the same experimental setup described by *Di Risio et al.* [16] and later by *Romano et al.* [17] and, by applying the wavenumber-frequency analysis (k-f) on the records of shoreline displacement, they pointed out that the 0th-order edge wave mode is the only one relevant for shoreline runup.

*Heller and Spinneken* [18] performed a large number of 2D experiments in a wave flume dealing with subaerial block-shaped landslides. In their experiments they investigated, among others, the effect of three block model parameters (i.e. the landslide Froude number, the relative slide thickness, and the relative slide mass). They provided empirical equations for the maximum wave amplitude, height, and period. Moreover, by comparing the newly derived equations as obtained for blockshaped landslides with the available equations for granular landslides, they found that block-shaped landslides do not necessarily generate larger waves than granular slides.

In 2015, *Heller and Spinneken* [19] presented a new set of 3D experiments carried out in a wave tank dealing with subaerial block-shaped landslides. The authors compared the new 3D results with past 2D experimental ones, published by the same pair of Authors [18], taking advantage of the identical boundary conditions between the two sets of data. Several parameters (i.e. water depth, landslide volume and density, landslide release positions) have been changed during the new experiments. Therefore, the Authors provided some empirical equations to predict the 3D offshore and laterally onshore wave properties, identifying the waves decay law both for 2D and 3D configurations, and providing very useful discussion on the existing 2D-3D conversion formulae (e.g. *Watts et al.* [20]).

In 2016, *Romano et al.* [17] published a series of new 3D experiments dealing with tsunamis generated by semi-elliptical subaerial landslides occurring at the flank of conical islands. As pointed out by *Di Risio et al.* [16], the physical model at hand aims at reproducing, in a Froude law scale, the Sciara del Fuoco slope (see **Figure 3**), i.e. a natural sliding surface located at the Stromboli Island (Southern Thyrrenian Sea, Italy). The main objective of the experiments is to provide a benchmark dataset for the validation of numerical models of landslide-generated tsunamis. To this end, a quite unique acquisition system, consisting of both fixed and movable wave gauges, has been deployed and used. The experimental procedure is per se a novelty as each experiment consists in repeating several times the same landslide event, by changing for each repetition the position of the movable gauges, then obtaining, after checking the repeatability, a single virtual experiment with high spatial resolution measurements. Two different semi-elliptical landslide bodies have been used for the experiments (see **Figure 3**) in order to investigate the effects of the landslide volume and thickness, revealing that the mentioned parameters affects significantly only the wave amplitudes, especially in the near field,

*Physical and Numerical Modeling of Landslide-Generated Tsunamis: A Review DOI: http://dx.doi.org/10.5772/intechopen.93878*

### **Figure 3.**

*Pictures of the Sciara del Fuoco (Stromboli island) and the slide placed on the conical island model. (a) Detail of Sciara del Fuoco: rock fall. (b) Detail of the slide along the conical island. (c) Aerial view of Sciara del Fuoco. (d) Lateral view of the conical island and the slide.*

while for the wave periods (and celerities), a weak dependence upon these landslide parameters can be observed.

The studies cited so far are related to subaerial landslides. Few are the recent experimental works dealing with submerged landslides. Indeed, the experimental modeling of submerged landslide presents a wide range of physical restrictions. Therefore, clever technical solutions have often been employed (e.g. *Enet and Grilli* [21], *Liu et al.* [22], Watts [23]). Nevertheless, it remains the practical difficulty of exploring in detail the influence of some key governing parameters, as for instance the initial acceleration *a*0. This parameter is commonly recognized to be a crucial one in the slide kinematics, in particular in the initial phase, when the energy transfer between the landslide and the water takes place [1, 20, 21, 23–26]. Several experimental studies explored the importance of *a*0 by means of different techniques. *Watts* [23] changed the landslide's density to obtain different values of *a*0. In 2017, *Romano et al.* [27], using the same physical model described by *Di Risio et al.* [16], *Romano et al.* [11, 17], used a mechanical system controlled by an electric motor to perform parametric 3D experiments by changing the kinematics of a semielliptical submerged landslide. The experimental results pointed out that as the initial acceleration increases, then the rising time of the first wave trough decreases and, in general, the wave signals exhibit a shorter wave periods. This findinds have been recently numerically confirmed by *Romano et al.* [28] (see Section 3). As far as submerged landslides are concerned, a note on the use of rigid landslide models is

due. Although this represents an approximation of the real submerged landslide behavior, it is well demonstrated in the scientific literature (e.g. *Grilli et al.* [24]) that the landslide deformation does not play a significant role on submarine landslide tsunami features in the slide early time kinematics, which at short time scales is mainly governed by the initial acceleration.

Finally, innovative physical model approaches, by using rigid landslide models, have been recently used by *Perez del Postigo Prieto et al.* [29] to reproduce a coupledsource tsunami generation mechanism due to a 2D underwater fault rupture followed by a submarine landslide. Furthermore, 2D experiments have been employed to interpret the dynamics of complicated recent events, like the eruption of the Anak Krakatoa volcano (Indonesia) in December 2018. To this end, it is worth noticing the study of *Heidarzadeh et al.* [30], that applied a combination of qualitative physical modeling and wavelet analyses of the tsunami as well as numerical modeling to propose a source model of the Anak Krakatoa event.

## **2.2 Deformable landslide models**

Quite various are the physical model tests dealing with deformable landslide models. In 2010 Heller and Hager [31] performed 2D experiments dealing with subaerial landslide by using granular slide material. The large number of tests (more than 200) aimed at exploring the influence of several governing parameters, namely: still water depth, slide impact velocity, slide thickness, bulk slide volume, bulk slide density, slide impact angle, and grain diameter. As a result, the Authors provided empirical predictive equations for all relevant wave characteristics, e.g. maximum wave height, the maximum wave amplitude (including its location and period in the slide impact zone), and both the wave height and amplitude decay and the period increase in the wave propagation zone. Furthermore, the Authors present a comparison of the presented equations with the 1958 Lituya Bay case, finding a good agreement.

In 2012, *Mohammed and Fritz* [32] carried out a massive 3D experimental campaign aimed at studying the tsunamis characteristics generated by subaerial deformable granular landslides occurring at a plane slope, using a novel approach based on a pneumatic landslide generator to control the landslide impact characteristics. In their study they found a robust correlation between the wave characteristics and the landslide Froude number, providing also some quantitative calculation of the landslide-water energy converted rate. Moreover, a deep discussion on the wave amplitudes decay, wave celerities and comparison with other 2D and 3D landslide tsunami studies is provided.

In 2014, Viroulet et al. [33] published the results of some 2D experiments dealing with subaerial landslides sliding along a rough slope. The Authors investigated mainly the influence of the slope angle and the granular material, by using three different granular materials (spherical glass beads with two different diameter, non-spherical sand), on the initial amplitude of the generated leading wave and the evolution of its amplitude during the propagation. Interestingly, the presented experiments aim at investigating the tsunami characteristics generated by landslide characterized by Froude number smaller than one. As stated by the Authors, this situation is particularly relevant to model tsunamis generated by cliff failures located just above the sea surface, which are characterized by low impact velocities.

A unique series of large-scale 3D physical model experiments is described in 2016 by *McFall and Fritz* [9]. In this study the Authors investigated the runup features, measured both on the same coast at which the landslide occurred and on an opposing hill slope, of tsunamis generated by subaerial granular landslides occurring both at planar coast and conical island. The pneumatic landslide generator


*3.2. Methods*

In this stage, 3D printed concrete paving stones were produced in accordance with TS 2824 EN 1338 [15]. To observe the pumpability and printability characteristics of a cementbased mortar, experiments were carried out in the Construction Materials Laboratory of the Faculty of Engineering of Zonguldak Bulent Ecevit University. The initial and final setting times of the fresh mixture were measured through the Vicat Needle test.

In this study, a new 3D printer was designed and produced (Figure 1). The printer chassis was formed with a 30 × 30 aluminum sigma profile. Plastic parts produced from FDM (fused deposition modeling), stainless steel bolts, and nuts were used. Flexible plastic elevations were attached to the printer's feet to prevent mechanical vibration. The movement in the axes was provided by three Nema 17 step motors utilizing the delta arm design. A double extruder was used to mix cement-based mortar and accelerator admixture during the printing process. Flow settings in each extruder were made using mechanical and software calibrations. Cement-based mortar and accelerating admixture were extruded using a stepper motor and archimedean screws. In the calibration phase, the open source computer supported Repetier Host program was used. Stages such as step settings of the axes, speed, and acceleration were performed through the Repetier Host program. The stl (standard triangle language) file format of the paving stones was sliced with the open source G-code (program language of CNC machines) generator, and then was saved to the SD card. Production was started via the control panel by inserting the SD card into the printer.

**Figure 1.** Three-dimensional printer designed for this study.

Three-dimensional printed paving stone samples were cured using a standard water curing protocol. The compressive strengths of the hardened concrete were measured to elucidate the development of its strength over time in accordance with TS EN 12390-3 [16]. After that, they were compared with those for reference paving stones as per the standard TS 2824 EN 1338.

The machines and equipment required to carry out the above mentioned tests are available in the Construction Materials Laboratory of the Faculty of Engineering of Zonguldak Bulent Ecevit University.