Development and application of a moire fringe technique to the analysis of a structural knee

The technique of making inexpensive diffraction gratings of a quality suitable for moire fringe strain analysis is described together with a method of viewing the gratings for best results. The use of a reference grid avoids the need for resolving fine lines. A secondary moire pattern obtained by interfering two primary patterns from different loads is used to measure displacements and eliminates imperfections from the gratings. The strain and displacement patterns in knee joints tested by this method are described, and some analytical methods of solving for stress and strain distributions are investigated.