Thomas R. Bieler

TL;DR: In this paper, a review of continuum-based variational formulations for describing the elastic-plastic deformation of anisotropic heterogeneous crystalline matter is presented and compared with experiments.

TL;DR: In this paper, the effect of alpha platelet thickness on the plastic flow of Ti-6Al-4V with a transformed microstructure was established by conducting isothermal, hot compression tests at hot working temperatures on samples with identical crystallographic texture and beta grain size.

TL;DR: In this paper, a crystal plasticity-finite element (CP-FEM) based model of an extensively characterized microstructural region has been used to determine if the stress-strain history provides any additional insights about the relationship between shear and damage nucleation.

Abstract: The size and crystal orientation of Sn grains in Pb-free, near eutectic Sn-Ag-Cu solder joints were examined. A clear dependence of the thermomechanical fatigue response of these solder joints on Sn grain orientation was observed (Sn has a body centered tetragonal crystal structure). Fabricated joints tend to have three orientations in a cyclic twin relationship, but among the population of solder balls, this orientation triplet appears to be randomly oriented. In thermally cycled joints, solder balls with dominant Sn grains having the particular orientation with the c-axis nearly parallel to the plane of the substrate were observed to fail before neighboring balls with different orientations. This results from the fact that the coefficient of thermal expansion of Sn in the basal plane (along the alpha-axis) is half the value along the c-axis; joints observed to be damaged had the maximum coefficient of thermal expansion mismatch between solder and substrate at the joint interface, as well as a tensile stress modes during the hot part of the thermal cycle. Localized recrystallization was observed in regions of maximum strain caused by differential expansion conditions, and its connection with crack nucleation is discussed.

TL;DR: In this article, the effect of slip transfer on heterogeneous deformation of polycrystals has been a topic of recurring interest, as this process can either lead to the nucleation of damage, or prevent nucleations of damage.