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I have research interests in - Mechanical Behavior of Materials, Electromagnetic Fracture, Development of new age Thermal Interface Materials
Projects
1. Fracture due to electromagnetic forces alone in an edge cracked conductor
FEM simulations showed that electromagnetic forces act on an edge crack to open it in mode I condition. Experiments were successfully conducted to validate the FEM results, proving that the self-induced electromagnetic forces alone can cause sharp crack propagation in an edge-cracked conductor (a thin Al foil of thickness 12 µm in this case) as long as the stress intensity factor due to the self-induced electromagnetic force (which is a body force) was higher than the critical stress intensity factor of the material. Furthermore, an increase in the current density (to a certain limit) increased the rate of crack propagation. Moreover, it was observed that the crack propagated by a finite amount per electric pulse and it became incrementally longer with continued pulse loading. Therefore, the crack propagation under electric current loading can be assumed to be stable and hence very well controlled.
2. Identification of parameters controlling the transition of sharp crack propagation into blow hole formation
The transition of propagation of sharp crack into blow hole formation occurred either at larger normalized crack lengths (a/w ≥0.8) while keeping the same applied current density or at very high current densities (more than that required for sharp crack propagation) while keeping the same crack length. FEM simulations showed that the heat affected zone significantly increased ahead of the crack tip at both very large current densities and the large normalized crack lengths and hence produced conducive conditions for the formation of blow holes. The size of the blow hole was directly linked to the size of the heat affected zone ahead of the crack tip. Hence, depending on the nominal current density and normalized crack length, a crack may propagate in sharp fashion or as blow holes. This work was submitted to Engineering Fracture Mechanics and is currently under review.
3. Fracture at lower critical current density upon simultaneous application of mechanical loading
Effect of simultaneous electric current and mechanical loading on the crack propagation behavior in an edge-cracked conductor was further explored. FEM simulation revealed that under combined electromagnetic and mechanical loading, the stress components as well as stress intensity factors due to these two stimuli can be linearly superimposed to determine the overall stress intensity factor. Experiments conducted under combined electromagnetic and mechanical loading showed that the critical electric current density required to propagate a crack decreased. Moreover, application of mechanical load at an angle to the crack faces (i.e., under mixed mode loading), caused deflection of crack at an angle upon passage of an electric current pulse. The angle of deflection under mixed mode conditions was predicted by standard mixed-mode fracture mechanics principles. Sharp crack propagation under mixed mode conditions of simultaneous electric current and mechanical loadings on an edge cracked conductor in shown in Fig 3.
4. Development of Thermal Interface Materials and Interconnects for Next Generation Microelectronic packaging
Thermal interface materials should have high thermal conductivity and high shear compliance. Such materials may be produced via liquid phase sintering (LPS), which enables uniform distribution of the high melting phase (HMP) constituents in the low melting phase (LMP) matrix. The thermal conductivity of optimized Cu-In based solders was shown to be at least 2 times higher than that of pure In with only ~50% increase in the yield strength of the composite relative to the pure indium.
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