Physical Mechanisms Governing the Intersonic and Supersonic Decohesion of Bimaterials: Effects of Interfacial Strength, Loading Rate and Confining Pressure

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An analytical study will be conducted of the physical phenomena associated with highly dynamic decohesion of bimaterial interfaces and simple unidirectional composites. Specific goals of the project are to establish the necessary conditions for dynamic bimaterial decohension in various regimes (subsonic, intersonic, and supersonic) and to characterize the associated physical phenomena. To accomplish these goals, material combinations and processing techniques will be chosen that allow for the variation of interfacial strength, confining pressure and mismatch of mechanical properties (most importantly wave speeds) across the interface. In addition, loading configurations will be selected that can provide a range of impact velocities. Analytical studies will be undertaken to develop a theoretical framework by which the experimentally observed transient intersonic and supersonic shear dominated mechanical fields can be qualified in terms of appropriate fracture parameters. Thermal fields resulting from the observed large scale frictional contact and the associated energy dissipation will also be investigated. Experimental measurements of the deformation fields and thermal fields in the vicinity of a dynamically loaded or propagating interfacial crack will be performed in real time using ultra-high speed optical and thermographic diagnostic techniques. The deformation fields will be characterized using high speed photography in conjunction with two optical techniques: Coherent Gradient Sensing (CGS) and dynamic photoelasticity. Temperature fields near shear dominated intersonic and supersonic intrfacial cracks willb measured using a recently developed high speed infrared camera in order to study local mechanisms of energy dissipation.