Towards a More Complete Understanding of PMN-PT 4 Point Bend Specimen Behavior

ASTM Standard C1161 is often used to determine fracture performance of piezoelectric materials. The basic geometry of C1161 is a four-point beam subjected to mechanical loading. When single crystal PMN-PT was recently subjected to this test unexpected results were observed. Fracture did not occur at the defects incorporated into the specimens nor did failure occur at locations of where maximum stress or strain was predicted by mechanical analyses. Computational tools were then applied to determine piezoelectric material response in this geometry with applied mechanical loading. Conventional finite element codes with piezoelectric material constitutive response using linear behavior models were used. Rather than duplicate the experimental work, the goal of this analysis was to provide insight into the electric fields that would be generated due to mechanical loading of the four-point bend specimen and the resulting variations in stress and deformations. Variation in poling directions is examined. Three different four-point bend configurations are considered. In each specimen the poling direction is aligned with one of the axes of the geometry. The computational study was done as a pre-screening analysis to determine if further understanding of the piezoelectric phenomenon could be expected in a series of experiments of similar design. Experimental work is currently under development based on the computational results of this study. The intent is to used computational analysis to advance understanding to enhance experimental design.