Uniaxial time-dependent ratchetting of SiCP/6061Al composites at room and high temperature

The uniaxial strain cyclic characteristics and time-dependent ratchetting behaviour of T6-treated SiCP/6061Al alloy composites were studied by experiments at room and high temperature (573 K). The cyclic softening/hardening feature and ratchetting behaviour of T6-treated composites with two volume fractions of SiC particulates and un-reinforced matrix were discussed under different loading conditions including some time-related factors, such as loading rate, peak stress hold and so on. It is shown that: the particulate reinforced metal matrix composites present similar strain cyclic characteristics and ratchetting behaviour to those of un-reinforced matrix in macro-scale, i.e., the ratchetting also occurs in the composites under asymmetrical cyclic stressing, and the ratchetting strain increases with the increasing of stress amplitude and mean stress; however, the addition of SiC particulates into the matrix increases the resistance of the composite to the ratchetting, and the ratchetting strain decreases as the volume fraction of SiC particulates increases. It can be concluded that the ratchetting behaviour of the composites has great time-dependence at room and high temperatures, the variations of stressing rates and with or without peak stress hold influence the ratchetting greatly, and the interaction of creep and cyclic plasticity is remarkable, even at room temperature. Some significant conclusions are obtained, which are useful to construct a constitutive model to describe the time-dependent ratchetting of the composites.