TWA 25
Creep / Fatigue Crack Growth in Components
This TWA was a follow-on to earlier successful TWAs that focused on high temperature test methods. Previously, TWA 11 was involved in developing a new high temperature test method for measuring the creep crack growth properties of materials using the creep fracture mechanics parameter C*. The method was restricted to ductile situations and was contained in ASTM test procedure E 1457.
This methodology was extended under TWA 19 to conditions where only limited creep deformation was observed. As a consequence, recommendations were made to incorporate conditions of greater brittleness into the original procedure, and a revised standard was produced. However, it was recognized that further work was needed to apply these procedures to actual components.
For design and safety assessments, industry needed assurances that creep crack growth properties measured on laboratory specimens could be applied to real components. Laboratory specimens usually contained through-thickness cracks whereas components mostly experience partially penetrating defects. The size of a component and the stress state in it may also be different to that of the laboratory specimens. Some experiments had already been carried out on 'feature' components, representing realistic situations, to measure crack growth. However, no accepted procedure existed for interpreting the results. The purpose of this TWA was to address this issue by performing analysis of these results.
See also
More information
Contact the VAMAS Secretariat - select this link