investigation of Elasto-Plastic Interfacial Crack Tip Fields Using Infrared Interferometry

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The current understanding the influence of plasticity effects on the interfacial fracture has been modest despite of the practical significance in a wide range of dissimilar material systems including metal-ceramic, metal-metal and polymer-metal sandwiches. The work in this area has largely remained analytical/numerical in nature and experimental investigations are needed to further relate the local and global parameters and gain insight into the crack initiation and growth behaviors as in case of elastic counterparts. A detailed experimental study of the similarities of crack tip fields, mode-mixity, J-dominance, crack growth resistance, to name a few, would be valuable for modeling interfacial crack initiation and crack growth. To this end, an experimental effort on interfacial fracture behavior of bi-materials that are elastically similar but plastically dissimilar is proposed using a newly developed infrared interferometer. The research is aimed at gaining insight into the asymmetries introduced by plasticity near the interfacial crack tip in bimaterial specimens that are dissimilar in their plastic characteristics but identical elastically. The above effort will utilize an infrared Twyman-Green interferometer recently developed by the PI for investigating crack tip fields in full-field, real-time, non-contacting mode even in the presence of extensive plasticity and surface roughening. In this technique, the limitation of the surface roughness/texture encountered with the onset of plasticity/damage when using visible light has been circumvented through a favorable roughness to wavelength ratio. The method also offers advantages such as greater latitude in working with surfaces in 'as-is' condition and it does not need reference exposures.