Optical Stress Analysis of Flexural Waves in a Bar

A complete, direct, full-field optical determination of dynamic stress distributions by a combination of photoelastic and interferometric measurements is illustrated. The method is applied to the study of flexural waves propagating in a photoelastic, urethane rubber bar. A displacement type of transverse, dynamic loading (which has approximately the form of a decaying sine wave) is applied at one end of the bar. The loading pulse can be repeated with good precision. Individual isochromatics and isoclinics are obtained, using a still camera with a short duration (0.5 micro sec) flash. A series of isochromatics have also been obtained with a Fastax high-speed motion picture camera. Photoelastic data are supplemented by isopachic patterns obtained by a modified method of holographic interferometry recently developed by the authors. As an example of complete determination of stress distributions, a vectorial representation of the principal stresses at one instant is given. Comparisons are made with approximate theories.