Residual stress measurements in fibre reinforced titanium alloy composites

The residual stresses in two Ti/SiC unidirectional composite panels with thick cladding were measured using two experimental methods. The variation of in-plane residual stresses in the cladding of the materials was measured by using a crack compliance method, and the average fibre stresses were inferred from the results. The applicability of a simple bending theory for the calculation of the residual stresses from curvature measurements was confirmed by a finite element analysis. Using a matrix etching method, the longitudinal fibre strains were measured from the relaxation of fibres upon dissolving the matrix in a part of the composite. The stresses in the fibre and the matrix were then calculated using a concentric cylinder model. By combining the results of both methods, the out-of-plane stresses were also determined, so that the full stress state in the reinforced section of the material could be obtained.