FRACTURE CRITERIA FOR VISCOELASTIC AGING SOLIDS

A subcritical crack propagation in aging viscoelastic solids is studied on the basis of the local fracture criteria (the critical crack opening displacement criterion and the Knauss energy criterion). The deformation of an aging viscoelastic material is described in accordance with the linear hereditary aging theory. It is shown that the crack growth equations derived from both these criteria coincide for solids subjected to steady external loadings and differ by a time-dependent term if the external loading is time-varying. The durability of a cracked solid evaluated in accordance with the Knauss criterion is shorter than that evaluated in accordance with the critical crack opening displacement criterion, if the loadings are time-varying. The equations of the growth of cracks in aging solids are analyzed and solved.