RESIDUAL STRESS DISTRIBUTION BENEATH THE FATIGUE FRACTURE SURFACE OF Al/SiC(WHISKERS) COMPOSITE

Abstract The X-ray fractographic technique was applied to characterize the fatigue fracture surface on Aluminium alloy (A6061) reinforced with SiC whiskers (Al/SiCw) prepared by the modified squeeze casting method. The X-ray elastic constant was first determined for the diffraction profiles of Al(222) plane as -88.2 MPa/deg. by using Cr-Ka radiation and a modified four point bending method. Then, the distribution of the residual stress on and beneath the fracture surface was measured, and used for the estimation of the depth of the plastic zone. The results were discussed in connection with the fracture mechanics and a fracture process. The plastic zone size was related to the maximum stress intensity factor Kmax divided by the 0.2% proof stress. The residual stress in the vicinity of the fatigue fracture surface was tension. Its value gradually increased and decreased with increasing the depth below the fracture surface. Its distribution beneath the fracture surface was also characterized as a composition of three residual stress distribution models: the distribution caused by monotonous plastic deformation near the crack tip, that relieved by surface roughness and that resulting from the compressive deformation due to crack closure.