Residual Stress in Polycrystalline Alumina: Comparison of Two-Dimensional Maps and Integrated Scans in Fluorescence-Based Measurements
Chris A. Michaels, Robert F. Cook
The spatially heterogeneous residual stress fields in a series of three polycrystalline alumina materials are compared using two fluorescence-based measurement techniques. In the first technique, 18 hyperspectral arrays of the Cr-based R1 and R2 ruby fluorescence line shifts are formed into two-dimensional maps of stress components, and experimental stress distributions are calculated using both spectral lines jointly. In the second technique, the data are formed into integrated scans reflecting the average spectra within the maps and assumed Gaussian stress distributions are calculated, using the spectral lines singly. Comparison of the distribution parameters shows that the single-peak-based integrated scan technique significantly overestimates the variation of the mean crystallographic stresses relative to the two-peak-based two-dimensional map technique. In addition, the integrated scan technique suggests standard deviations for the crystallographic stress distributions that are significantly greater than those determined from two-dimensional map observations. Although, when a sufficient area of the microstructure is examined, the averaged results of the two techniques agree, the two-dimensional map method is preferred as it makes full use of the two- peak spectra and provides explicit stress distribution determinations. For the approximately 15 m grain size materials examined here the c-axis stress distributions determined from the mapping technique were characterized by means ± standard deviations of approximately (190 ± 40) MPa.