Residual stress is an important factor for evaluating the deformation and failure of engineering materials. Diffraction-based measurement assumes that the full measured lattice strain tensor contributes to residual stress according to Hooke s Law. The present work focuses on the lattice strain determination of individual grains in a dual-phase stainless steel (DPSS) by means of differential-aperture X-ray micro-diffraction (DAXM). The results show that the residual stress only takes part of the responsibility of the total measured lattice strain. In fact, the compositional variation inside the material was found to cause greater strain gradient in both ferrite (α) and austenite (γ) phases in DPSS. Therefore, quantification of compositional and residual stress effects on lattice strain was conducted in order to evaluate the true residual stress inside engineering materials.
Electrical-thermal-mechanical behavior of materials plays an important role in controlling the structural integrity of electromechanical structures of small volumes. The electromechanical response of Cu strips was studied by passing an electric current through the strips with electric current densities in the range of 12.34 to 29.60 kA/cm2. The passage of the electric current of high current densities introduced electrical-thermal-mechanical interactions, which caused grain growth and grain rotation in both the melted region and heat-affected zone. The electrothermal interactions led to the elastoplastic buckling of the Cu strips with the maximum deflection of the Cu strips increasing with the increase of the electric current density. The total strain is a quadratic function of the electric current density. There was a quasi-steady state in which the electric resistance of the Cu strips linearly increased with time before the occurrence of electric fusing. A power-law relation was used to describe the dependence of the time-to-failure (electric fusing) on the electric current density. For the region of relatively low current densities, the current exponent ranged from 17.9 to 44.6, and for the region of high current densities, the current exponent ranged from 2.5 to 5.2. The current exponent for relatively low current densities decreased with increasing the length of Cu strips, showing size-dependence. Finite element analyses were performed to analyze the current-induced deflection of a Cu strip. The simulation results showed that the maximum deflection for the electric current density larger than or equal to 5 kA/cm2 is a linear function of the current density in agreement with the experimental observation.
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