Use of CDM in Materials Modeling and Component Creep Life Prediction

Abstract

Physically based continuum creep damage mechanics (CDM) has been reviewed and shown to provide a unifying framework for some seemingly diverse methods of predicting design and remanent creep lifetimes. These methods—theta projection, omega parameter, Larson-Miller parameter, and Robinson’s life fraction rule—exhibit certain strengths in common with CDM, but also weaknesses which CDM identifies and avoids. CDM consists of sets of coupled rate equations for inelastic strain, internal stress, and microstructural evolution (damage) which can then be integrated under boundary conditions appropriate to the test or service operating conditions: constant load/temperature for creep; constant total strain for stress-relaxation, variable stress/temperature, etc. Other state-variable approaches to creep and cyclic plasticity (for example, those due to Bodner, Miller, Chaboche, and Robinson), differ from CDM mainly in concentrating on the primary/secondary stages of creep (or cyclic work-hardening) and/or by their introduction of damage in an empirical Kachanov manner. The application of physically based CDM to LCF/thermal fatigue and its potential for predicting lifetimes of welded joints are also discussed. [S0094-9930(00)00903-3]

Characterisation of microstructure and creep properties of alloy 617 for high-temperature applications

“…The nature of the predictive creep model discussed in the following section does not require the exact species of the precipitates, as long as their hardening contribution is known [15]. In this case the precipitates have all been considered as having a positive hardening contribution, assuming that their hardness is sufficient to result in dislocation bypass rather than cutting.…”

“…In particular, the parameters of interest in the present investigation are the type of phases present in each specimen, their volume fractions, particle size and inter-particle spacing (IPS), as a function of time, temperature and stress [13,15].…”

“…The approach follows the reasoning of Dyson [15], adapted more specifically for high alloy ferritic steels by Yin and Faulkner [13]. The four microstructural damage parameters are as follows: 1) D d , a dislocation damage parameter based on the accumulation of a dislocation distribution occurring up until the end of primary creep; 2) D s , a solute hardening parameter based on the changes in solute hardening caused by various matrix element partitioning effects occurring during the various precipitation sequences that takes place during exposure at high temperature; 3) D p , a precipitation hardening parameter describing the hardening caused by precipitates during creep exposure at high temperature, which is essentially related to the inter-particle spacing where: D p = 1-(P i /P), P i being the initial inter-particle spacing and P being the inter-particle spacing after time t; 4) D n , a cavity density term describing the structural integrity of the material in the creep fracture crack path, which is usually the grain boundary.…”

A Coupled Creep Plasticity Model for Residual Stress Relaxation of a Shot Peened Nickel-Base Superalloy

“…The plasticity model is based on the von Mises effective stress with a nonlinear mixed isotropickinematic hardening rule as described by Dodds [30]. The creep model follows the physics-based modeling of dominant deformation mechanisms similar to the approaches of Ashby, Dyson, McLean and others [13,[21][22][23][24]. Based on the SEM and TEM observations of the shot peened and thermally exposed microstructure, it has been argued that the microstructure remains stable over the range of temperatures and exposure times in this study [38].…”

“…Initial approaches to represent material degradation under creep loading include the continuum damage mechanics (CDM) approaches of Kachanov [16] and Rabotnov [17] that incorporate a single damage parameter and associated evolution equation. More recently, the simple damage parameters in the CDM approach have been replaced by specific degradation models representing mechanisms such as cavity nucleation and growth, subgrain coarsening, multiplication of mobile dislocations, and thermally and environmentally driven mechanisms [18][19][20][21][22][23][24].…”