Abstract

Dynamic photoelasticity was used to study some fundamental aspects of wave propagation in layered media and to obtain information on the dynamic state of stress associated with the various waves generated by a point source explosion. Columbia Resin CR-39 and aluminum were used to obtain a model with an acoustical impedance-mismatch between layers of 6 to 1. A Cranz-Schardin multiple spark camera, operating at approximately 200,000 frames per second, was used to record the dynamic isochromatic fringe patterns associated with the propagating stress waves. Small charges of lead azide were used to explosively load the models.Six different wave types were clearly identified. In the region near the explosive detonation, the predominant waves were the incident P 1 wave and the reflected P 1 S 1 waves from the interface and the free boundary. In regions away from the explosive detonation the headwaves (P 1 P 2 S 1 , P 1 S 2 P 1 , and P 1 S 2 S 1 ) dominate since their rate of attenuation is much lower than the rate associated with the incident dilatational or the reflected shear waves.The data obtained in the form of isochromatic fringe patterns were converted to individual values of the principal stresses in several instances. The methods developed for this separation are applicable whenever the dilatational or distortional waves occur alone. The separation method requires no auxiliary data other than the isochromatic fringe orders and yields dynamic displacement data in addition to the individual values of the principal stresses.

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