Modelling of damage development and failure in notched‐bar multiaxial creep tests

Abstract

Finite element predictions of creep rupture in notched specimens are presented in this work. A damage mechanics model linked to the creep strain rate and stress triaxiality has been adopted in order to predict creep life under multiaxial stress conditions and the predicted creep failure strain and time to rupture have been compared with experimental data for a C-Mn steel tested at 360 o C. Finite element analyses have been conducted for primary-secondary (PS) and primary-secondary-tertiary (PST) creep laws. As expected a PST analysis gives more conservative predictions than a PS analysis. An additional term was included in the model to allow for an increase in hydrostatic strain due to creep damage. Under certain conditions incorporating this 'elastic damage' term can lead to an increase in the predicted failure time (i.e. it is less conservative). A further enhancement to the model was to include the effect of crack growth through the use of a nodal release technique. It was found that the predictions obtained using the nodal release technique were very similar to those from the PST creep model with elastic damage. Furthermore, it was found that the inclusion of plasticity (i.e. rate independent inelastic strains) may decrease the conservatism in the prediction (an increase in the predicted life). The sensitivity of the results to the value of the uniaxial creep failure strain and the stress triaxiality model used in the definition of damage were examined and it was found that both these factors strongly affected the predicted rupture time. Mesh size effects were also examined and the finite element predictions were seen to be quite mesh sensitive with a finer mesh giving more conservative predictions.

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

“…In previous work [12], [13], FE results of the type shown in Figure 7 have been compared with the NSW model. Here, the predictions from the NSW-MOD model are also considered.…”

“…A 'virtual' fracture testing procedure using the finite element (FE) method [12][13][14] has been developed to predict creep crack growth rates in Carbon Manganese CT specimens. It has been found that uncoupled continuum damage methods can be used to predict creep crack growth within a numerical framework [14].…”

“…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)…”

The creep of alloy 617 at 700 °C: Material properties, measurement of strain and comparison between finite element analysis and digital image correlation

“…(4) , it no longer has the ability to take the load. Thus it is assumed that the stress components in all directions will be zero in the elements concerned, which is simulated in a similar manner to Yatomi et al (2004) , Oh et al (2011) , Kim et al (2013) and Mehmanparast et al (2014) whereby the material properties of the damaged element (i.e. its stiffness) are reduced to a near-zero value.…”

Creep Crack Initiation in a Weld Steel: Effects of Residual Stress

“…To predict the onset of crack growth a creep damage approach is used following the approach in [9]. A damage parameter, ω, is defined such that 0 ≤ ω ≤ 1 and failure occurs when ω = 1.…”