MICRO-LEVEL STRAIN MEASUREMENT: HITTING THE BUFFERS WITH OPTICAL METHODS

摘要

Optical methods have been hugely successful in the determination of strain fields and the validation of theoretical and computational models. In recent years, their capabilities have been extended by the use of computational processing of the optically delivered information. This combination has been particularly powerful as a means for revealing increased detail of strain fields. However, in the matter of how far we may proceed in this quest for detail - the minimum gauge-length that we may consider - is something that we must address if we are to avoid the equivalent of what, in ordinary optical terms, is called "empty magnification", with consequent erroneous conclusions. Three aspects are to be considered: (1) the fringe structure, i.e. to what extent can low-frequency fringes carry high-frequency information? (2) Limits inherent in the optical system, i.e. how much detail can the system actually see and what distortions does it introduce? (3) the restrictions imposed by the recording and interrogation system.