Continuum versus discontinuum damage mechanics of creep caused by microcracking

• Published in: International journal of fracture Vol. 101; no. 3; pp. 181 - 201
• Main Authors: Salganik, Rafael L, Gotlib, Victor A
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01-02-2000
• Subjects: Brittle materials; Continuum damage mechanics; Crack initiation; Creep (materials); Deformation mechanisms; Evolution; Fracture mechanics; Mechanical properties; Mechanics; Microcracks
• ISSN: 0376-9429; 1573-2673
• DOI: 10.1023/A:1007677529834

The effect of evolution of damage, mainly microcrack damage, on creep and creep fracture of brittle materials (or materials exhibiting brittle-like behavior under certain temperature and loading conditions) is treated theoretically. A comparative analysis of two basic approaches is given:(i) continuum damage mechanics (CDM), and(ii) discontinuum damage mechanics (DDM). The first approach deals, from the very beginning, with continuum abstract description of damage with the help of field quantities.The second approach considers the macroscopic mechanical behavior of the material affected by damage evolution in terms of individual damage units, such as microcracks or/and microvoids. A serious conceptual deficiency of the CDM approach is pointed out and analyzed. This deficiency is associated with the CDM basic notion of the effective stress, understood as the stress (referred to undamaged area) which governs the deformation of the material per se in the presence of damage. This deficiency becomes apparent in the case when damage is caused by a multitude of cracks (microcracks). In this case, the damaged area, as it is defined by CDM, is actually the area occupied by cracks. As this area is negligible, the effect of damage on the mechanical behavior of the material, according to CDM, would be negligible either, irrespective of the cracks concentration, which is in deep contradiction with reality. It is shown how the situation can be improved with the aid of DDM and how the macroscopic creep behavior relates to the structure and strength parameters of the material when considering the mechanism of damage evolution in terms of thermal activation.