Predicting Microstructural-Level Residual Stresses and Crack Paths in Ceramics
V.R. Vedula, Sandia National Laboratories, Albuquerque, NM 87185

S.J. Glass, Sandia National Laboratories, Albuquerque, NM 87185
W.C. Carter, Massachusetts Institute of Technology, Cambridge, MA 02139
D.M. Saylor, G.S. Rohrer, Carnegie Mellon University, Pittsburgh, PA 15213

Residual stresses arise in ceramics due to thermal expansion anisotropy. The magnitude of these stresses can be very high and may cause spontaneous microcracking during the processing of these materials. In addition, the microstructural level stresses are likely to play a significant role in where cracks initiate and propagate under macroscopic loading too.

The crystallographic orientation data obtained by backscattered electron kikuchi patterns (BEKP) was used to predict the residual stresses in alumina. An object oriented finite element analysis package OOF - developed at NIST was used to perform the computations. A code (OIM-2-PPM) was developed to import the orientation data directly into OOF. Using this methodology, residual stresses in relatively large microstructures (approx. 500+ grains) were predicted. Microcrack initiation and propagation in alumina was also simulated using grain boundary energy data obtained from AFM groove measurements.

Indentation cracks were introduced to determine if certain boundaries were more susceptible to cracking than others. The misorientations and predicted stresses at grain boundaries that fractured in OOF were compared to the experimental data.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-ACO4-94AL85000.