Experimental and numerical studies on the crack behaviour in X6CrNi1811 under conditions of primary and secondary creep

It is shown experimentally that creep crack growth rates da/dt can be described by the C* integral in the stainless steel X 6 CrNi 1811 (similar A304) at 600deg C. Under steady-state conditions C* and da/dt are correlated by a power law independent of size and geometry of the specimen. This power-law correlation is in accordance with theoretical predictions if plane stress conditions are assumed to hold. A description of crack growth rates by the stress intensity factor K delivers creep crack growth curves which depend on specimen size and geometry. Creep crack growth takes already place immediately after loading the specimens. In the regime of primary creep, its time dependence corresponds to theoretical considerations. Load-line displacements V and the C* integral are evaluated numerically bt the finite-element method. If a plane stress state is assumed good agreement will be achieved with experimental results. (orig.)