MEASUREMENT OF RESIDUAL-STRESSES IN METAL-MATRIX COMPOSITES

Metal matrix composites (MMC) are expected to develop internal residua l stresses on cooling from fabrication due to the large thermal expans ion mismatch between reinforcing fibers and the matrix. This work was undertaken to measure experimentally these residual stresses and compa re them with analytical calculations in order to establish clearly the ir levels and dependence on material parameters. Two techniques for re sidual stress measurement were investigated. (1) X-ray diffraction (si n2-psi method) and (2) neutron diffraction. Both techniques gave resul ts in good agreement with analytical predictions for several systems ( SCS-6/Ti-24A1-11Nb, W/NiA1, and Al2O3NiA1). The results obtained showe d a dependence of residual stresses on thermal expansion coefficients, elastic moduli, volume fraction fibers, and matrix yield strengths. T he fibers showed compressive stress states, and the matrix, tension. A verage stresses were higher in the fiber direction than transverse to fibers.