High-resolution stress mapping of polycrystalline alumina compression using synchrotron X-ray diffraction

Abstract

The ability to achieve uniform stress in uniaxial compression tests of polycrystalline alumina is of significance for the calibration of piezospectroscopic coefficients as well as strength studies in ceramics. In this study high-energy X-rays were used to capture powder diffraction profiles over a half-section of a polycrystalline alumina parallelepiped sample under an increasing uniaxial compressive load. The data were converted to strain and results were used for stress mapping of the sample. Stress maps from the study quantify the higher stresses at the sample-platen contact interface and reveal the evolution of the stress distribution in these specimens with load. For the geometry of the samples used, at the center section of the specimen the overall magnitudes of the compressive stresses were found to be 20% higher compared with the average expected theoretical stress based on the applied load and cross-sectional area. The observed compressive stresses at the corners of the parallelepiped specimen were 62% higher and shear stresses were observed at the specimen interface to the load mechanism. The effects, seen at the interface, can lead to premature failure at these locations and can affect the accuracy of calibration of spectral peaks with stress as well as compression strength measurements. The results provide important information that can be used to establish guidelines on material and geometry considerations in developing compression tests on high-strength ceramics.

Optical stress probe:in-situstress mapping with Raman and Photo-stimulated luminescence spectroscopy

“…ence flaws, voids or nanoparticle composites [13]. For polycrystalline alumina such measurements within a sample are comparable to similar results from x-ray diffraction [14,15]. The fundamental mechanics of materials can be investigated as stress distributions of various shapes and sizes are studied.…”

“…Additional inhomogeneity of the peak shift of R1 could also be caused by residual stress across the surface, and thus variation in R1 peak position [11]. The complexities in achieving uniform compression over high strength ceramic samples where high loads are coupled with small cross-sectional areas is discussed in other work [15].…”

Stress-Sensing Nanomaterial Calibrated with Photostimulated Luminescence Emission

“…with a 4:1 aspect ratio per ASTM D695. This ratio was specifically chosen to avoid edge effects caused by the friction between the sample surface and the platen during loading experiments and was previously observed in ex situ studies of compression tests on polycrystalline alumina …”