Modeling of processing-induced residual stresses in gamma titanium composite materials

An experimental study of the residual stress formation and evolution in Gamma -Titanium based composite material was completed for some important processing and heat treatment conditions. A concentric cylinder model based on Norton's creep law with the coefficients replaced by new terms related to time and temperature was developed by a combination of viscoplasticity and thermoelastic analysis of a concentric cylinder domains representative for the matrix and the fiber. X-ray diffraction technique was used to measure average residual stresses at the neighborhood of Sapphikon fibers. The composite was fabricated by HIP'ing (hot isostatic pressing). The residual stress at the matrix decreased as the temperature of the heat treatment increased up to an "optimum" value after which the residual stress started to build up inspite of the increase in the annealing temperature. This phenomenon was depicted through the numerical model as well as in the XRD (X ray diffraction) and microhardness indentation.