PARTICLE-SIZE, VOLUME FRACTION AND MATRIX STRENGTH EFFECTS ON FATIGUEBEHAVIOR AND PARTICLE FRACTURE IN 2124 ALUMINUM-SICP COMPOSITES

The effects of particle size, volume fraction and matrix strength on t he stress-controlled axial fatigue behavior and the probability of par ticle fracture were evaluated for 2124 aluminum alloy reinforced with SiC particles. Average particle sizes of 2, 5, 9 and 20 mum and volume fractions of 0.10, 0.20 and 0.35 were examined for four different mic rostructural conditions. Tensile and yield strengths and fatigue life were substantially higher in the reinforced alloys. Strength and fatig ue life increased as reinforcement particle size decreased and volume fraction loading increased. The frequency of particle fracture during crack propagation was found to be dependent on matrix strength, partic le size and volume fraction and on maximum crack tip stress intensity. Particle fracture can be rationalized, phenomenologically, by the app lication of modified process zone models, originally derived for stati c fracture processes, and weakest link statistics which account for th e dependence of matrix yield strength and flow behavior and particle s trength on the probability of particle fracture during monotonic fract ure and fatigue crack propagation.