P.P. Sinha

Anisotropy in Residual Stress Measurements in Aluminum Alloys Used in the Aerospace Industry

The aerospace industry has encountered many failures of the metallic hardware and sub-systems made of aluminum alloys, wherein the residual stresses are known to play a major role. This requires an accurate measurement of the residual stresses at various locations of the component in a nondestructive manner. The X-ray diffraction (XRD) method of measuring the residual stresses offers one of the most commonly used nondestructive techniques providing accurate stress values. The aluminum alloys, used for launch vehicle and satellite applications, are subjected to a variety of processing operations to realize the final product. These processes invariably introduce crystallographic texture in the material, which, in turn, influences the residual stresses measured using the diffraction method. The sin2ψ–2θ plots show nonlinearity in the longitudinal and transverse direction for the alloys studied. This nonlinearity could be caused by two major factors, namely, the crystallographic texture and stress gradient from the surface to the core of the sheets. In the case of aluminum alloys studied, both the factors play important roles by influencing the residual stress measurements. This paper covers the anisotropy in residual stress measurements caused by the influence of texture using the diffraction technique. Experiences at the Vikram Sarabhai Space Centre (VSSC) have been discussed with case studies on textured aluminum-alloy materials.