A Description of Crack Growth From Defects Under Creep Conditions

Abstract

Methods previously used to describe crack growth under creep conditions are reviewed. Under some conditions, materials can be notch insensitive and a model is developed based on engineering analyses of creeping structures using reference or skeletal point stresses. This stress, dependent on crack length and geometry, is derived for conventional test pieces. Examination of the relaxed stress distributions around stress concentrations suggests that the behavior of cracked structures is dependent on the total creep strain/stress index, p. Two categories of materials behavior are distinguished: when p>5, the reference stress description should be applicable and when p→1, the stress intensity factor description appears appropriate. Finally, the general applicability of the model is discussed with respect to the metallurgical aspects of creep damage accumulation, suggesting that crack initiation may dominate life when p>5 and crack growth when p→1. A comparison is then made with previous experimental data.