An experimental investigation of the fracture mechanics of interfacial cracks in a bimaterial using the local collocation method

The primary goal of this work was to develop a complete methodology for experimental evaluation of fracture mechanics parameters for interfacial cracks in coated materials subjected to thermal boundary conditions. Three separate aspects of the problem needed to be addressed. First, the moire interferometry experimental method needed to be introduced to the photomechanics laboratories at Texas A&M University; the basic method was also refined to make it compatible with the available equipment and loading conditions. Also, the resulting full field displacement information needed to be analyzed in such a way that fracture parameters could be deduced; this was accomplished using the local collocation method and singular value decomposition. Finally, the results needed to be evaluated by comparison with results obtained using an independent method. The quality of the results was judged using quality of fit criteria, reconstructed fringe patterns, and comparison with analytical or computational results.; The methodology was developed incrementally using homogeneous mode I mechanically loaded specimens, bimetallic thermally loaded specimens, and bimaterial specimens that incorporated coatings. The results indicate that linear elastic fracture mechanics expressions are valid when applied to interfacial cracks in coatings, and that this methodology can be used successfully in the evaluation of fracture mechanics parameters. The research incorporates new concepts into the evaluation process, such as checking and correcting for ill-conditioning in experimental mechanics overdeterministic methods, using embedded thermocouple data for determination of boundary conditions in related computational models, and the use of explicit expressions for the interfacial crack tip expressions that incorporate nonzero bimaterial parameters and truncated series expressions. Suggestions for future research efforts related to and building on this work are also described.