editorial ‘why did it fail?’

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Post on 21-Jun-2016




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  • T. J. Baker

    EDITORIAL 'Why did it fail?' Engineers and materials scientists have eve o, reason to be proud of the spectacular developments in design and materials usage which have taken place in all branches of engineering in recent years. Unfortunately, all too often we are brought sharply back to earth by the failures. Catastrophics which may result in widespread injury or loss qf life such as aeroplane crashes, marine disasters and accidents involving chemical or nuclear installations are mercifully few in number. However they receive world-wide publicity and bring discredit on the engineering profession. The vast majori O, offailures are never reported. Yet they occur ever)' day of the year and, taken together, represent an enormous financial loss and involve considerable personal iniurv.

    All failures demand investigation irrespective of whether they result in disaster or just inconvenience. This may be motivated by considerations of public safety or by commercial considerations of profitability. In either case the objective is the same, to identify the factors responsible so that appropriate remedial action can be taken to avoid a recurrence.

    Prominent amongst the experts involved in such investigations is the materials" technologkt. He is the only person able to determine the condition of the materialprior to failure. Only he can ident~v latent defects, deficiencies in the processing of the materials or an)' deterioration which may have developed during service by processes such as fatigue, corrosion or wear. Also in the case of failures involving fracture, he is the only one able to decipher the mechanism ofl'racture and thereby identify the type, and in man), cases the magnitude, of loading necessao' to have caused the failure. Usually, of course, the materials specialist does not work in isolation and one of the most constructive features Of many .failure enquiries is the close collaboration between scientists and engineers of various discipfines.

    Only ver), rarely does a.failure investigation reveal a totally new phenomenon which could not have been predicted on the basis of existing knowledge. The essentialproblem is that those who are in possession of this knowledge are often not sufficiently involved in the engineering design process.

    Traditionally the engineer has relied on the materials" specialist to supply materials which satisfy certain specification requirements and possess a .fen, well defined engineering properties. The application of the material is then determined to a large extent by established design rules and regulations. Such rules are based mainly on previous experience and sooner or later due to innovations in design or changes in operating conditions, traditional materials cease to perform in a satisfactory manner and existing design criteria become invalid.

    Obviously there is a need.for industry to have a greater awareness of the factors affecting the performance of materials in service. It is, however, unreasonable to expect the mechanical or chemical engineer to acquire this detailed knowledge in addition to all the engineering skill which is his primary concern. For example, in addition to the basic mechanical properties of the material, he should be aware o fal l the hazards which may occur during fabrication and use. He needs" to know the limitations of the material, its defect tolerance, its resistance to fracture under all possible conditions of loading, its ability to withstand various environments and the types of deterioration which may occur in service. Also he must know those features of the material which require inspection and how frequently such inspections need to be carried out. This information can and must be supplied by the materials specialist.

    AII manufacturers have a responsibilio, to produce reliable products by safe working processes. Increasingly this responsibility is becoming clearly and legally defined by the introduction of legislation relating to Health and Safety at work, consumer protection and product liability. To satisfy these statutoo' requirements there must be much closer liaison between the engineer and the materials specialist during the initial design of an engineering enterprise, during manufacture and throughout the service life.

    Usually a failure investigation results in the identification of a number of technical factors which have combined in such a way as to cause failure. Rarely is it admitted that the .fundamental cause was a lack of communication between the engineer and the materials specialist.