Prediction of creep crack growth from uniaxial creep data

Abstract

In this paper uniaxial tensile creep data are used in conjunction with fracture mechanics concepts to predict creep crack growth rates in materials having a wide range of creep ductilities. A model is proposed of creep damage accumulation in a process zone ahead of the crack tip. The model allows all stages of creep to be incorporated in an approximate manner and creep ductility to be stress and stress-state sensitive. Good agreement is obtained with experimental crack growth data on a range of low alloy steels, a stainless steel, an aluminium alloy and a nickel-base superalloy. It is found that cracking rate is insensitive to the creep process zone size but inversely proportional to creep ductility. Crack growth rates under plane strain conditions are shown to be about fifty times those for plane stress loading.

Crack growth in the presence of limited creep deformation

“…The largest spread in results is demonstrated by the steel which exhibited significant plastic deformation on loading. However, this spread is consistent with the scatter commonly observed when extensive creep deformation accompanies cracking [1,[6][7][8].…”

“…It is relevant to situations involving extensive creep where a steady state creep stress distribution has been established ahead of a crack [1,[6][7][8]. Certain restrictions are imposed to determine when this condition has been reached.…”

“…These include stress intensity factor K [2][3][4][5], the creep fracture mechanics parameter C* (and the C(t), C t , and Q* variants of this parameter) [6][7][8][9][10][11], the reference stress σ ref acting on the remaining ligament of a cracked structure [12][13] and a local crack tip opening displacement rate Ý [14][15]. Typically when these parameters have been applied to describe creep crack growth data on particular materials, cracking rate where A, D o , H, m, φ and p are material constants which may be temperature and stress state dependent.…”

Probabilistic analysis of creep crack initiation and growth in pipe components

“…When creep dominates it is characterised by C* [8,[12][13][14][15][16]. For the case when N = n, identical stress fields are produced for the plastic and creep situations and similar methods can be employed to calculate both J and C* [13].…”

“…It is important to note that the accepted procedure in the codes [1][2][4][5] is to estimate residual lives in components from 'benchmark' data derived from CT specimens using the C* approach [12][13][14].…”