Grain Reorientation and Stress-State Evolution During Cyclic Loading of an a-Ti Alloy Below the Elastic Limit
Rachel Lim1, Darren Pagan1, Paul Shade2, Joel Bernier3, Anthony Rollett4
1Pennsylvania State University, 2Air Force Research Laboratory, 3Lawrence Livermore National Laboratory, 4Carnegie Mellon University
Local stress state and grain orientation evolution are tracked through 200 cycles of loading at 90 % of Ti-7Al’s yield strength using high energy x-ray diffraction microscopy to elucidate the microscale plastic deformation that occurs during nominally elastic macroscopic cyclic loading. Significant changes in the stress state occur during the first loading cycle to relieve initial microscale residual stresses. Additionally, examination of the aggregate of grains through subsequent cycles shows continuous lattice reorientation and evolution of von Mises stresses within grains despite the macroscopic loading remaining below the elastic limit. Lattice orientation and maximum resolved shear stresses applied to grains are found to highly influence the activation of specific slip systems and, as a result, the direction of lattice reorientation.
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