Dynamic interfacial fracture: Experimental observations and criteria
This experimental study investigates the dynamic decohesion of bimaterial interfaces. Two different bimaterial specimen geometries are employed to obtain the complete range of crack-tip speeds in the subsonic regime. The dynamic loading is achieved either by detonating two explosive charges on the specimen or by impacting the specimen in one-point bend configuration. The resulting fracture process is observed using dynamic photoelasticity in conjunction with high-speed photography. The full-field information obtained in the form of isochromatic fringe patterns are analyzed to obtain various parameters of interest such as crack-tip velocity, complex stress intensity factor, dynamic energy release rate and mixity using the available stress field equations.^ Early experimental efforts resulted in a special specimen geometry to obtain the initiation, propagation and arrest in a single experiment. The bimaterial interface in this case is subjected to planar tensile waves by detonating explosive charges on the specimen. The experimental data is utilized to obtain the initiation and arrest toughness values in a single experiment.^ In the second stage of the investigation, the interface inclination is changed to vary the initiation mixity. The dependence of the dynamic initiation and arrest toughness on the mixity under dynamic loading is also investigated. The results show that the initiation toughness is higher than the arrest toughness by about 21%. The experimental data was utilized in the early developments of a generalized fracture criterion.^ Further experimental and analytical investigations resulted in two dynamic fracture criteria, namely, exponential crack profile growth criterion (ECPG) and vectorial crack-face displacement criterion for subsonic crack growth along the interface. These criteria are based on the premise that the crack-face displacements at a point behind the crack tip increase exponentially with the instantaneous crack-tip velocity. This assumption establishes a generalized relationship between the dynamic energy release rate and the instantaneous crack-tip velocity. Experiments are performed on PSM-1/aluminum bimaterial systems for both shear dominated and opening-mode dominated crack growth to verify the proposed criteria. Two different bimaterial specimen geometries are employed to obtain the complete range of crack-tip speeds in the subsonic regime. The dynamic loading is achieved either by detonating two explosive charges on the specimen or by impacting the specimen in one-point bend configuration.^ A series of experiments are conducted to understand the effect of interface curvature on the interfacial crack propagation. In these experiments, the interface curvature is varied and the interface is subjected to opening mode dominated loading conditions. The results show that as the interface curvature decreases the peak velocity increases. Also, it is observed that the crack-tip velocity-mixity relationship depends on the interface curvature. The experimental data fits very well with the proposed interface fracture criteria.^ The attention is then focused on to the intersonic regime of the interfacial fracture. A parametric investigation has been carried out to study the influence of various fracture parameters on the isochromatic fringe patterns using recently developed stress field equations. A numerical scheme based on Levenberg-Marquardt least squares minimization method is developed to obtain the relevant fracture parameters from the experimentally obtained fringe patterns. The results are utilized to evaluate a recently proposed intersonic interfacial fracture criterion. ^
Applied Mechanics|Engineering, Mechanical
"Dynamic interfacial fracture: Experimental observations and criteria"
Dissertations and Master's Theses (Campus Access).