I am currently looking for materials, which return into their relaxed form/ position after intense bending/ stretching.

Could you please let me know what is the name of this mechanical property, so that I could search further on this topic?

Do you know any examples for such materials? Perhaps some polymers?

  • $\begingroup$ rubber, elasto-polymer... $\endgroup$ – Solar Mike Sep 23 '17 at 13:40
  • $\begingroup$ As a point of interest, there are also Shape Memory Alloys. SMAs can return to their original shape after large strains. Wikipedia provides a nice overview of the topic. $\endgroup$ – CableStay Sep 23 '17 at 22:49

It depends exactly what application you are looking for.

The amount of stress a material will tolerate is defined by its tensile strength and the amount it will deform under a given stress is defined by its Young's Modulus (low Young's Modulus is flexible high is stiff)

If you want something which will stretch by a large percentage of its original dimensions then rubbers (generally classified as elastomers) tend to be good. Typical applications include things like engine mountings and flexible covers for articulated joints. Rubbers also tend to be self-damping and so are good for vibration isolation.

In terms of maximum stress resistance then spring steels are widely used, these tend to be medium carbon, low alloy steels which are hardened and tempered. These materials have very good tensile strength and toughness. Although steel as a material has high stiffness, you can control the degree of flexibility of a spring by its shape (eg coil springs) or by mechanical linkages as in the case of torsion springs. Overall steel tends to be the preferred for high performance springs although you do see polymer and composite leaf springs eg in commercial vehicles.

Another option for some applications is polymer textiles and rope, for example the dynamic ropes used in climbing here the way that yarns are formed and woven also contribute to their flexibility. These tend to be used for impact absorption and are effective at moderating high impact loads without failing although they may be damaged by loads close to their ultimate capacity.

  • $\begingroup$ Thank You for the information about the Young's Modulus and the following examples. $\endgroup$ – Anfad Sep 24 '17 at 9:19
  • $\begingroup$ I am looking forward to create a filigree structure, which can be stretched. It should return to its initial position when not streched, without deformation. $\endgroup$ – Anfad Sep 24 '17 at 9:28
  • $\begingroup$ In that case it sounds like an elastomer is a good option to look at. I think that rubber sheet can be laser cut for 2-dimensional profiles. Another option is RTV silicone, which can be cast pretty easily, a variety of types are available, sued for mould-making and theatrical prosthetics etc. $\endgroup$ – Chris Johns Sep 24 '17 at 18:10
  • $\begingroup$ Thank you very much, Chris! I would like to use the surface for the human body. Do you know any rubber or RTV silicone, which is compatible with the human skin? $\endgroup$ – Anfad Sep 25 '17 at 8:01
  • $\begingroup$ Cured silicone is generally fine for skin contact, and the food or prosthetics grade stuff definitely is (barring allergies). Latex rubber is fine in itself but allergies to it are not that uncommon. $\endgroup$ – Chris Johns Sep 25 '17 at 22:58

The word you are looking for is hyperelasticity. Material models from this field of study are useful for rubberlike materials that are expected to not exhibit plastic deformation.

  • $\begingroup$ Thank You! I can't understand the difference between elastic and hyperelastic. Could you please give some examples for hyperelastic materials? $\endgroup$ – Anfad Sep 27 '17 at 9:12
  • $\begingroup$ Hyperelastic materials (e.g. rubber-like polymers and elastomers) can have very large deformations without yielding, and without residual strain. Think of a rubber band, you can stretch it quite a lot (several hundred % strain), let it go, and it will snap back to it's original length. The yield strain for typical elastic materials, such as metals, are much lower, e.g. steel, with a yield strain around 0.002%. Real-world elastomers are not totally hyperelastic in that they also have residual strain and time-dependent behavior. The field dealing with this behavior is called viscoelasticity. $\endgroup$ – Austin A Sep 28 '17 at 12:09

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