Application of Neutron Diffraction to Measure Residual Strains in Various Engineering Composite Materials

An experimental neutron diffraction technique was used to measure residual strains that developed in multiphase composite materials during postfabrication cooling as a result of thermal expansion mismatch or volume expansion due to change in crystal structure. The reinforcement geometries that were studied include unidirectional fibers, randomly oriented single crystal whiskers, and equiaxed particles. Both metal and ceramic matrices and reinforcements were considered. In some cases, the measured data compared fairly well with predictions based on simple elastic models. In other cases, either creep was shown to relax the residual strains during cooling, or the interpretation of the measured data contained uncertainties due to texture in the samples or lack of a clearly defined crystal structure for the reinforcement phase.