Creep crack growth prediction using a damage based approach

Abstract

This paper presents a numerical study of creep crack growth in a fracture mechanics specimen. The material properties used are representative of a carbon-manganese steel at 360 o C and the constitutive behaviour of the steel is described by a power law creep model. A damage-based approach is used to predict the crack propagation rate in a compact tension specimen and the data are correlated against an independently determined C* parameter. Elastic-creep and elastic-plastic-creep analyses are performed using two different crack growth criteria to predict crack extension under plane stress and plane strain conditions. The plane strain crack growth rate predicted from the numerical analysis is found to be less conservative than the plane strain upper bound of an existing ductility exhaustion model, for values of C* within the limits of the present creep crack growth testing standards. At low values of C* the predicted plane stress and plane strain crack growth rates differ by a factor between 5 and 30 depending on the creep ductility of the material. However, at higher loads and C* values, the plane strain crack growth rates, predicted using an elastic-plastic-creep material response, approach those for plane stress. These results are consistent with experimental data for the material and suggest that purely elastic-creep modelling is unrealistic for the carbon-manganese steel as plastic strains are significant at relevant loading levels.

Theoretical and numerical modelling of creep crack growth in a carbon–manganese steel

“…The results are from a single batch of material and performed within a collaborative programme, [28]. The relevant mechanical properties are given in Table 1 [14]. Figure 5 shows the steady state CCG rate for the C-Mn steel.…”

“…8) for plane stress and plane strain using the material properties in Table 1. The uniaxial failure strain, ε f , used in both model is 18%, which is the measured value from uniaxial creep tests [14]. The additional parameters needed for the NSW and NSW-MOD model are listed in Table 2.…”

“…In this work, an uncoupled damage-based approach is used to simulate crack growth from the initial transient state to the steady state regime, within a finite element framework. The approach follows that in [12]- [14], whereby nodes are released when damage reaches a critical value, simulating the formation of a sharp crack. The analysis focuses on the study of CCG in a carbon manganese (CMn) compact tension (CT)…”

Prediction of crack growth in a nickel-based superalloy under fatigue-oxidation conditions

“…Crack growth criterion proposed in the current work is essentially a strain-based approach, which has been widely used for the prediction of viscoplastic failures such as creep [e.g., [37][38][39]. The strains local to a crack tip are of multiaxial nature such that an accumulated strain, which accounts for all strain components, is often adopted as a damage parameter [e.g., [37][38][39][40].…”

“…The strains local to a crack tip are of multiaxial nature such that an accumulated strain, which accounts for all strain components, is often adopted as a damage parameter [e.g., [37][38][39][40]. This parameter is also used in the current work, where the progressive nature of the accumulative plastic strain with cycles, as opposed to the relative constant stress response, is considered to be the main crack driving force [15], and as an alternative to other criteria such as plastic work or J-integral approaches.…”