Evaluation of Thermal Stresses in Continuous Alumina Fiber-Reinforced Aluminum Composites by X-ray Stress Measurement

Abstract

An X-ray diffraction technique was applied to determine both the matrix and fiber stresses during thermal cycling processes for a continuous fiber FP (α-alumina)/A1 composite as well as for a continuous γ-alumina/A1 composite. In-situ X-ray stress measurements at all temperatures throughout the test range were automatically carried out in a vacuum furnace mounted on a computer-controlled diffractometer, which had been improved in such a fashion that the conventional sin2 Ψ method could be used. It was confirmed that, when the composite systems were subjected to a change in temperature, thermal stresses were induced in the matrix and fibers because of the mismatch in thermal expansion coefficients between the two phases, and that the resultant stresses in the matrix and fibers balanced each other in the composites. Furthermore, it was proved by the X-ray method that, during the cooling process of the composite, the matrix was plastically deformed in tension, and during heating, in compression. The Al matrices of the two composite systems were observed to deform in a similar manner during the thermal cycle. The X-ray technique is shown to be useful for evaluating the thermal stresses as a function of the temperature of a composite.