 a required function.
detailed analysis of the traditional approach and to explore the possibility of devising a broader notion which is able to giảm giá with the problematic cases. In doing so, this paper aims to give ethics of engineering a more accurate and present-day understanding of failure in engineering, in tư vấn of its analysis of responsibility, liability and risks.
various stakeholders involved in the different stages of a product life cycle.
“The Life Cycle Approach in Action”. Finally, “Conclusion” summarizes and concludes the paper.
(2009) notice that the “looseness of the terminology and often overlapping shades of meaning lead to ambiguity and confusion”. Prasad et al. (1996) raise the same concern from the point of view of dependable computing where the “terminology […] is used non-uniformly by many authors and standards”.
reproduced in Fig. 1.
defined as the sự kiện in which the observed performance trespasses the acceptable limits, after which the item is said to be in a fault state. The figure makes clear that the term ‘termination’ in the IEC definition should not be interpreted as total lack of ability to perform, but as the trespassing of the acceptability levels. Indeed, after a failure sự kiện an item can still be capable of performing the required function, albeit a disappointing level.
then the partial failure is considered of to be a “major” one; finally, the end of the spectrum are “complete” failures which consist in the “complete inability to perform all required functions”.
It is interesting to note that the IEC vocabulary does not make provision for gradations of fault. This means that for a given item and a given function, the notion of fault is binary: either the item performs that specific (minor or major) function within the limits or it does not.
level builds up gradually (e.g., because the item is progressively wearing out), then the ensuing sự kiện is termed a “gradual failure”; while a sudden drop beyond the acceptable limits qualifies as a “sudden failure”.
when least one performance parameter has exceeded the acceptable limits.
system or component to perform its required functions within specified performance requirements.
Fault: (1) A defect in a hardware device or component; for example, a short circuit or broken wire. (2) An incorrect step, process, or data definition in a computer program.
definitions” section of the recent standard on Analysis techniques for system reliability (IEC 60812, 2006), the definitions of failure and fault are taken literally from the IEC vocabulary but a note is added claiming that “for historical reasons” the two terms will be used interchangeably.
component or equipment no longer can perform its intended function safely” (emphasis added).
defects (emphasis added).
A failure occurs when the item stops performing its required function” (emphasis added).
in the IEC and IEEE definitions, it is centered on the actual observable performance of the item.
variations shows that there are circumstances which engineers are willing to describe as failures but are not easily captured by the traditional definition.
these basic assumptions may not hold.
The traditional approach to failure can be analyzed in terms of four basic assumptions: missing functionality, utilization context, item level, and negativity assumptions. An sự kiện is an instance of failure in this approach when it satisfies all four assumptions.
assumption highlights the role played by the notion of an item’s function according to the traditional approach. The point is that items may behave in a number of aberrant ways and can possibly deviate from the specifications under several respects, but a failure is said to occur only when the performance of a required function is terminated, that is to say, it trespasses the acceptable limits.
Required function: a function or a combination of functions of an item which is considered necessary to provide a given service.
Service: a set of functions offered to a user by an organization.
definition of “function” is missing.
to have suffered a “gradual major failure”. In contrast, the gradual degradation of a sub-function that does not impair the essential function is called a “gradual minor failure”.
functions within the specified limits under specified conditions” (emphasis added).
Frawley’s definition implies that previously, the beginning of its useful life, the product was performing an acceptable level, after that its performance dropped and trespassed the acceptable limits.
stage and tests.
rate of a specific pump) and the target values and acceptable levels defined by the specifications. In fact, as users we are surrounded and are dependent on the ability of many physical items to satisfy our needs by actually performing their required functions: cars move us around, clocks tell the time, printers print paper, and so on. Many of our judgments refer to the properties and behaviors of these items with which we giảm giá on a daily basis.
level a certain product, say the Volkswagen Golf, can be judged to be more reliable than a different but comparable type, say the Ford Focus; yet it is possible to claim, without contradiction, that a specific Ford Focus item has been found to be more reliable than a specific Volkswagen Golf.
judgment about features that are shared among all items realized following the same architecture.
“Beyond the Traditional Approach”).
annoyances. Nonetheless, as remarked by Yellman’s (1999) criticism of Chillarege (1996) definition, engineers are willing to consider an underperforming product a failure whether or not the customers complain about it.
definitions and by other evidence in the literature, engineers are prone to consider as failures also events that do not square with this interpretation; that is to say, events that do not satisfy the four basic assumptions.
events constitute a failure or not, but they will maintain that, if something is a failure, then it should have been avoided. In the rest of this section it will be shown how the first three assumptions may not hold in some circumstances that are relevant in engineering practice.
trespasses the acceptable limits, the items are said to be in a state of complete failure. In contrast, items performing multiple required functions can suffer partial failures, which can be minor or major depending on the importance of the affected function. Anyway, for a given required function (minor or major), the difference between functioning state and fault state is straightforward and it is based only on the observed performance being within or without the acceptable limits.
product to meet or continue to maintain the performance or strength criteria in the application for which it was designed.
assessed in accordance to the traditional approach, the verdict would be the opposite, for the judgment would be based on the fact that the item is still operating within the specifications.
concrete, with the whole bridge riding on three castors, each one made of a steel shaft rotating within two bearing bushes manufactured from Oilon, a self-lubricating polymeric material. The bridge was in operation for 6 months and apparently was working as expected. Indeed, it was only during the first routine inspection that evidence of wear was found on the shafts of all three castors.
loading experienced by this swing bridge castor” (p.. 1634).
judgments based on clear-cut termination of a required function because the latter are more conspicuous and potentially more harmful.
parameters for the sintering process. It is clear that the traditional “termination of a required function” was not the criterion adopted by Sudhakar and Paredes when they claimed that the bearings suffered a “premature failure during manufacturing” and set out to identify the “failure mechanisms”.
manufacturer warranty. In this sense, a field return is a physical item that has failed to perform its required function. Engineers, however, generalize this property over the entire type of a product, in which case it becomes the rate of field returns and, as such, it does not belong to any item in particular but to the entire type.
Ford introduced a new type of ignition module, the so called Thick Film Ignition module, with the purpose of surpassing the reliability of Japanese cars which were invading the US market. This goal was translated into a requirement to the effect that the rate of field returns must not exceed 1.6 returns out of 100 modules installed (Pecht 2006; Qi et al.
modules installed on cars operated in colder regions. The point is, however, that, as a type, the Thick Film Ignition module was unable to achieve the expected rate of field returns.
criticisms point to crucial properties of the C5 as a type. The manufacturing quality and reliability of the physical items might have been excellent and many customers might have enjoyed riding it; yet, as a type, it was an uncontested failure.
safety or robustness or sustainability, especially in case of complex products, cannot be easily reduced to a specific function or small group of functions expressed as input and outputs in the functional hierarchy of a product. Still, type level characteristics are crucial for the realization of successful products and play an important role in the delineation of product requirements.
or process operational, functional, or design characteristic or constraint”. In turn, the notion of a design characteristic covers a wide spectrum of “performance, usability, safety, maintainability and a host of other qualities” (Hull et al. 2010, p.. 7).
the availability of a shared and clear-cut distinction between functional and non-functional requirements. What is needed is the acknowledgement that the traditional notion of failure is based, among others, on the assumption that functions of engineering products should be expressed by means of input–output relations of flows of energy, materials, and signals that can be organized in functional block diagrams. Many design methodologists, e.g., (Pahl et al.
this interpretation has to cover all relevant aspects of