|
Background |
|
|
|
The comments below set the context for the work being undertaken within the auspices of VAMAS TWA26. |
|
|
|
The past ten to twenty years has seen an enormous expansion in the development and availability of full field stress and strain measurement and analysis methods, which have potentially a very high value to industry. The current statutory requirement to satisfy standards and regulatory authorities requires that engineers test and validate models of structures with greater rigour. To do this, engineers must use methods that have been suitably validated. In addition increasingly difficult problems in design and development of new structures arise from a number of factors including reduced cost and development time. Full field optically based stress analysis methods in conjunction with numerical analysis must be seen as the safest, fastest and most cost effective way of solving these problems. The use of these methods also leads to a deeper understanding of the engineering problems and a reduction in the quantity of expensive testing. Enormous confidence can be gained from the correlation between measured stress and strain data and numerical analyses over the full field of a component. The adoption of this philosophy is essential in developing engineering knowledge as it provides a more certain basis for the design of engineering components. It is also superior to the current situation, where cross correlation between techniques is only carried out at discreet points on the structure. The vast majority of these full field techniques are optically based interferometric methods, which give direct or indirect measures of the surface deformations, stresses or strains. The most likely reason for the recent rapid development of these methods is the advent of smaller, cheaper and more powerful image collection and processing equipment, the most important of which is arguably the personal computer. Evidence of this immense interest is given in the recent publication by the IMechE devoted almost entirely to this class of techniques [1]. This journal edition contained seven papers of which six deal with full field optical techniques. The total number of references in these six papers was 374 and this list is by no means exhaustive. In addition to the significant amount of time devoted to research in these areas there is also great interest in industrial applications of these techniques. In particular, the development of an automated reflection polariscope [2] has been supported strongly by the aerospace industry as have ESPI (Electronic Speckle Pattern Interferometry) and shearography [3]. Shearography has already been introduced to the industrial production process for quality control of helicopter rotor blades [3]. The challenge, which the stress and strain analysis community must address, can be met by unification of the community to develop a cogent set of standards. These standards will form a framework within which industry can apply these methods and develop them further. It is important to obtain recognition and acceptance of full field optical techniques so that further investment in their future development can come from those who will specifically benefit. This investment will only come if industry can use the methods in a way that is accepted by the standards and regulatory authorities. The purpose of this paper can therefore be summarised as being a "call to arms" of the stress and strain analysis community to develop a set of recognised standards for optical methods. This must be done in an environment that will ensure success and investment in the future. |
|
|
|