Analysis of thermal residual stresses in unidirectionally aligned SiCw/Al-alloy matrix composites by X-ray diffraction

In aluminum alloy matrix composites reinforced with unidirectionally aligned SiC whisker, thermal residual stresses should be induced anisotropically in the composite due to the difference in the coefficients of thermal expansion between the matrix and whisker during quenching from high temperatures. The magnitude of thermal residual stresses in the matrix and whisker in various heat treated composites was investigated by X-ray diffraction method at triaxial stress states. Principal stress components (sigma(11), sigma(22), sigma(33)) induced in the water-quenched composites are high tensile stress stales in the matrix and compressive in the SIC whisker. On the other hand, the shear residual stresses to (sigma(12),sigma(23),sigma(31)) are almost zero. The tensile residual stress of the whisker axial direction (sigma(11)) in the composites is the largest value, and it agrees well with the tensile yield strength of the extrusion direction in the water-quenched SiCw/Al alloy composites. The tensile residual stresses of the composites restored at room temperature after cooling the water-quenched composites down to the liquid nitrogen temperature decrease remarkably compared to those of the water-quenched composites.