An Experimental and Analytical Program to Develop Crack Tip Fracture Criteria.

Abstract : A summary of progress on the development of instrumentation to determine with great accuracy the in-plane and out-of-plane surface deformations in the vicinity of a crack tip. The purpose is to establish a data base for a) guiding theoretical research in characterizing the deformation fields in the crack tip vicinity for fracture research and b) to provide factual information for the evaluation of currently proposed theories dealing with crack tip deformation. The experimental tools under development are (D Post's) moire interferometry for the in-plane ones deformations and optical interferometry for the out-of-plane ones. An essential part of this work is the implementation of a computer-based data processing unit, which is able to record and process in nearly real time fringe patterns into strain fields, and, for known - or estimated - constitutive behavior into stress fields. This report summarizes the state of developments with particular attention begin given to the elimination of problems in the vacuum deposition procedure for the metal film used in the moire interferometry. Also, insufficiencies with the optical recording system - insufficient collimation by available lenses - has been rectified. The development of a very efficient code for fringe image recognition by Fourier analysis is discussed.