Executive Summary : | Various engineering systems, such as microelectronic systems, MEMS and NEMS devices, exposed metallic structures during lightning strikes (e.g., airplane, wireless towers, etc.), superconducting magnets, etc. are subjected to large electric current densities during their service time. Such large current densities, when passed through the components of these systems, can produce several effects, such as significant Joule heating, electromagnetic forces, thermal stresses and shocks, etc. Since most of the engineering materials often contain defects like micro-cracks, micro-voids, etc, and are also mechanically stressed, these large current densities may cause propagation of these flaws, resulting in failure of components. My research agenda is based on understanding and identifying various failure mechanisms in thin metallic structures which are often subjected to such type of electric current surges and mechanical stresses during their service time. A two-stage approach will be employed to conduct the proposed study. Firstly, finite element method (FEM) simulations will performed, and distributions of current density, electromagnetic force, stress fields and electric current induced stress intensity factor will be evaluated for the cases of (i) electric current surges alone, and (ii) combined loading of electric current surges and mechanical stresses in metallic thin structure. This thin metallic structure will be formed of Cu based and Al based alloys which are important engineering materials in aforementioned applications. Subsequently, experiments will conducted to validate FEM results, where a custom-built experimental setup will be designed that can apply (a) short duration pulsed electric current (pulse width 50µm to 5 msec), i.e. to simulate electrical surges, and (b) a combination of pulsed electric current and mechanical load, at any angle between 0° to 90° relative to the crack, onto a pre-cracked thin sample. A correlation between the magnitude of applied short-duration electric current pulse, magnitude of the applied mechanical load and the failure in the sample either by crack propagation or blow-hole formation will be studied and results will be validated with FEM simulations. Fundamental understanding of these failure mechanisms will not only reduce the total number of “hit and trails” experiments, as prescribed in “design of experiments (DOE)” required for the design of new reliable small length scale systems, such as microelectronic packages, MEMS and NEMS devices but will also provide an essential tool for the diagnosis and solution of the problems in these existing devices/systems. Moreover, an attempt will be made to employ the knowledge obtained from this study to develop a novel tool-less machining technique for cutting thin metallic samples (thickness less than 100 µm). |