Fatigue damage evaluation in SiCp/2024 by X-ray diffraction method

A smooth specimen of an aluminum alloy 2024-T6 reinforced with 20 vol% of silicon carbide particles (SiCp) was fatigued under four-point bending. The X-ray diffraction method was used to measure the loading and residual stresses in each constituent phase. The phase stresses were determined from the diffractions of Al 2 2 2 and SiC 1 1 6. The compressive residual stress in both phases increased with increasing stress cycles. The half value breadth increased with number of stress cycles before final fracture. Difference between the phase stresses measured at the maximum load and zero load was examined during fatigue. The difference of the macro stress calculated from both phase stresses decreased with the number of stress cycles. The behavior can be divided into four regions. A lot of cracks in the matrix and decohesions at the interface were observed on the specimen surface. Decreasing of the difference of the macro stress was caused by the initiation and propagation of fatigue cracks. The effect of the stress relaxation by fatigue cracks was calculated on the basis of the crack density and the distribution of crack length. The maximum macro stress measured by the X-ray method was agreed well with the calculated value.