1.1 This test method covers the determination of time for a creep crack to grow on initial load (CCI) and its subsequent creep crack growth (CCG) rates in metals at elevated temperatures using pre-cracked specimens subjected to elevated temperatures under static or quasi-static loading conditions. The tests are validated for either base material (homogenous properties) or mixed base/weld material with inhomogeneous microstructures and creep properties. For CCI the time (CCI), t0.2 to an initial crack extension δai = 0.2 mm from the onset of first applied force and CCG rate, a˙ or da/dt are expressed in terms of the magnitude of creep crack growth relating parameters, C* or K. With C* defined as the steady state determination of the crack tip stresses derived in principal from C*(t) and Ct (1-14).2 The crack growth derived in this manner is identified as a material property which can be used in modeling and life assessment methods (15-25).
1.1.1 The choice of the crack growth correlating parameter C*, C*(t), Ct, or K depends on the material creep properties, geometry and size of the specimen. Two types of material behavior are generally observed during creep crack growth tests; creep-ductile (1-14) and creep-brittle (26-37). In creep ductile materials, where creep strains dominate and creep crack growth is accompanied by substantial time-dependent creep strains at the crack tip, the crack growth rate is correlated by the steady state definitions of Ct or C*(t) , defined as C* (see 1.1.4). In creep-brittle materials, creep crack growth occurs at low creep ductility. Consequently, the time-dependent creep strains are comparable to or dominated by accompanying elastic strains local to the crack tip. Under such steady state creep-brittle conditions, Ct or K could be chosen as the correlating parameter (8-14).
Product Details
- Published:
- 02/01/2013
- Number of Pages:
- 27
- File Size:
- 1 file , 410 KB
- Redline File Size:
- 2 files , 970 KB
