Strip yield models of creep crack incubation and growth

Abstract

The strip yield model of Dugdale and Bilby, CottreU and Swinden is applied to analyse the incubation and growth of creep cracks. This extends previous work by Vitek (on incubation) and by Heaton and Chan (following To) on growth.Following both Vitek and Heaton and Chan, the main criterion of crack growth used is a COD-based one. The crack is assumed to grow at constant crack opening displacement (COD) 4' = ~b,, and the creep strain ~ at the crack tip is assumed to be dplh, where the gauge length is a material constant.The COD-based theory indicates that the incubation and failure times t~, t I are controlled by the stress intensity factor K at large stresses, but by the net stress at very low stresses. A weakness of the theory is that it neglects primary-creep effects: these have to be absorbed by modifying the secondary-creep index. If this is done, then comparison with two independent experiments shows moderately good agreement with the COD-based theory for both t~ and t t.

Creep and Creep-Fatigue Crack Growth in Aluminium Alloys

“…According to Vitek (Vitek, 1977) this crack initiation would be governed by a critical value of the crack opening displacement. Ewing (Ewing, 1978) and Riedel (Riedel, 1977) using a modified Dugdale model, suggest that at high stresses:…”

High-temperature flaw assessment procedure: A state-of-the-art survey

“…The critical value of the COD for crack extension and the width of the plastic zone h are to be determined experimentally. Ewing 58 assumed the critical COD and related it to critical creep strain by expressing steady-state creep strain as COD/h. Primary creep was included by modifying the creep exponent.…”

Tensile cracks in creeping solids

“…Based on a Dugdale Model, Riedel [8] and Ewing [10] have worked out conditions under which the stress intensity factor is the relevant parameter for creep crack growth. More recently, Riedel [7] has confirmed these results by the analysis of a stationary shear crack (Mode III) in an isotropic material that is capable of elastic and creep deformation everywhere.…”