Initial Studies in Three-Dimensional Dynamic Photoelasticity

An initial study of stress waves propagating in a half space due to a point load on the surface has been accomplished by employing dynamic three-dimensional photoelasticity. The central plane of the half-space model was isolated for investigation by employing an embedded polariscope. Auxiliary experiments show that the thin elements of the polariscope do not significantly distort the stress wave as it propagates across the joints of the model containing the elements. Photographs of the dynamic fringe patterns were recorded with a Cranz-Schardin multiple spark gap camera operating at 400,000 fps. Three different waves were identified from the fringe patterns; namely, the incident dilatational and distortional waves and the reflected shear wave known as the von Schmidt wave. The data obtained for the shear wave in the form of isochromatic fringe orders were converted to individual values of the principal stresses along the axis of symmetry in the model. The method developed for separation of the principal stresses is only applicable when the distortional wave occurs alone along the axis of symmetry.