Techniques for non-birefringent objects: Coherent shearing interferometry and caustics

Shearing interferometric techniques that can provide information about the stress or deformation states of non-birefringent transparent materials and opaque specularly reflective materials are described. Two types of coherent shearing interferometers that provide full-field information about the gra dients of the stress state of an object are discussed. These techniques hav e recently found use in stress analysis, especially in experimental fractur e mechanics studies. In addition, a simpler technique called the method of caustics which is also applicable to non-birefringent materials is describe d in brief. This technique does not provide full-field information but has been of historical interest in experimental fracture mechanics. Examples of application of all three techniques are given.