FATIGUE CRACK-PROPAGATION CHARACTERISTICS IN SICP/6061-T6 COMPOSITE

Researches and developments concerning aluminum matrix composities which are excellent in specific strength and specific modulus have been reported and applications of aluminum matrix components are expected as the structural materials of composites of automobiles and aircraft. However, there are few reports on the fatigue crack propagation characteristics which are very important for the design of structural materials. Since composites fracture in a complicated manner such as exfoliation between matrix and reinforcement or failure of reinforcements. Therefore, such properties as well as tensil strength should be evaluated for the applications of aluminum matrix composites as structural materials especially from the viewpoint of the guarantee of higher security. The effect of volume fraction of SiC particles on the fatigue crack propagation characteristics of 6061 aluminum alloys reinforced with SiC particles (SiC(p)/6061-T6 composites) manufactured by powder metallurgy process were investigated. The following results were obtained. In a higher stress intensity range, unstable fatigue crack propagation was found as the threshold stress intensity range DELTA-K(th) and DELTA-K(eff.th) increased with increasing content of SiC particles. However, DELTA-K(eff.th) was suggested to be solely a function of the mean SiC particle size and to be independent of the volume fraction. This implies that for near-threshold crack extension, the maximum plastic zone size at the crack tip must exceed the mean SiC particle size.