Modelling of the cyclic ratchetting and mean stress relaxation behaviour of materials exhibiting transient cyclic softening

摘要

From experimental studies of 7050 aluminium, it has been observed that this material exhibits a much higher yield stress during initial monotonic loading than during subsequent cyclic loading. This cyclic softening plays an important role in the accurate prediction of cyclic stresses, and it has been noted that existing constitutive models cannot adequately address this issue. To characterise this softening behaviour, a method is proposed in which the Armstrong-Frederick type of constitutive model is associated with two sets of material constants, one for the initial monotonic loading and the other for the subsequent cyclic loading. The transition from the constants for monotonic loading to the constants for cyclic loading takes place upon the first reverse yielding. A comparison between experimental results and the model predictions shows that the softening model proposed here can accurately reproduce the experimental results for the initial half cycle, which, together with a modification of the dynamic recovery term in the non-linear kinematic hardening model, leads to significantly improved prediction of the cyclic response of the material.