Comparison of residual strains measured by X-ray and neutron diffraction in a titanium (Ti-6Al-4V) matrix composite

This research compares matrix thermal residual strains measured in a continuous fiber reinforced SiC/Ti-6Al-4V titanium matrix composite (TMC) using X-ray and neutron diffraction with finite element predictions. The strain dependence on the strains for several reflections (105, 204, 300, 213 and 312) of the matrix were explored at the surface (X-ray) and in the bulk (neutron). To determine the longitudinal surface strains from the X-ray measurements for comparison with the neutron values, the E-phi psi versus sin(2)psi plots were extrapolated to psi = 90 degrees. Continuum micro-mechanics based multi-ply finite element models (FEM) simulating rectangular and hexagonal fiber distributions were explored for calculating average surface and bulk strains. For different reflections, the experimentally determined surface measured strains ranged from + 1904 + 424 to + 2974 +/- 321 mu epsilon and the bulk measurements ranged from + 2269 +/- 421 to +/- 3022 +/- 1134 mu epsilon. These values contrast with the single valued FEM prediction of + 3200 mu epsilon which was the same for both the surface and the bulk. (C) 1999 Elsevier Science S.A. All rights reserved.