An interactive simulation technique to determine the internal stress states in fiber reinforced metal matrix composites

A new interactive experimental/mathematical technique designed to simulate composite behavior and determine the axial thermal residual stress in the matrix of the continuously reinforced metal matrix composite is described in this paper. This technique is based on the stress-strain expression in terms of the fiber thermal and mechanical properties as well as the volume fractions of the composite constituents. This expression is then incorporated into an experimental procedure in which a composite specimen is simulated by a fiberless (neat) titanium laminate plate gripped under load control across the frame of a hydraulic material testing system. The strain developed in the neat laminate specimen during heating or cooling is governed by the strain compatibility requirement imposed by the fiber phase which is represented by the testing frame. This restricted matrix strain is converted through a feedback logic into a matrix residual stress that could be followed on real time basis. The magnitude of the thermal residual stress measured at room temperature for a SCS-6/Ti-15-3 composite after the cool-down from consolidation temperature has been compared with that obtained by the X-ray diffraction technique. The proposed technique was then applied to a SCS-6/Ti-β21S composite to obtain measurements of the matrix thermal residual stress as a function of several testing variables such as temperature, heating/cooling rate, thermal cycle upper limit and number of thermal cycles. Important features of the matrix axial thermal residual stress have been analyzed. The major conclusion of this analysis is that the development of the thermal residual stress is dependent upon cooling rate while the relaxation of this stress depends on the magnitude of the viscoplastic strain generated in the matrix material at a particular testing condition. (orig.)