A Fracture Mechanics Approach to Creep Crack Growth

Abstract

A fracture mechanics approach was used to study high-temperature creep crack propagation. Crack growth rates were correlated with the C*-parameter which is an energy rate line integral. For materials conforming to a nonlinear stress and strain rate relationship in the steady-state creep range, specifically, those which can be properly idealized as purely viscous (negligible elastic and transient creep effects), C* characterizes the crack tip stress and strain rate fields. Crack growth rate tests were conducted in the creep range on a discaloy superalloy at 1200°F (920 K). Two specimen geometries were tested, a center cracked panel and a compact geometry, to establish the geometry independence of this approach. The results showed that crack growth rate correlated with the C*-integral, while other parameters (K and nominal stress) failed to adequately characterize crack growth rate.

A theoretical and computational framework for studying creep crack growth

“…A major feature of these studies is the development of a parameter that characterizes the crack tip fields as well as crack propagation. Under steady state creep conditions, the so called C * -integral (Landes and Begley 1976;Nikbin et al 1976;Ohji et al 1976) (i.e. the creep J -integral, Rice 1978) can be used to characterize the crack tip fields and creep crack growth.…”

Creep Crack Growth Behaviour of Alloy 718

“…The creep crack growth being an inelastic process, net section stress on (2) and reference stress 0 r (3) have been used to correlate with creep crack growth rates. In 1976, based on the modification of the J integral, a C* integral was suggested to be an appropriate parameter for creep crack growth (4)(5)(6)(7). However, the C* integral represents only the amplitude of the stress strain field ahead of the crack tip when a material is in steady state creep, but the stress relaxation around the crack tip due to creep deformation and crack propagation causes a nonsteady state creep process.…”

On the Mechanics of Surging Glaciers

“…It follows that any process of rupture or break-down that takes place very near the discontinuity will be controlled by J. We propose that the criterion for spread of the sliding region is that J equals or exceeds a critical value J c' A similar criterion has been proposed for the growth of cracks in creeping metals at high temperature (Landes and Begley, 1976). Similarly, the deepening of crevasses may be controlled by J and this will be discussed separately by McMeeking in future work.…”