Damage Model for Predicting the Effect of Steel Properties on Ductile Crack Growth Resistance

Abstract

This study pays attention to reveal material properties that control a resistance curve for ductile crack growth (CTOD-R curve) on the basis of the mechanism for ductile crack growth, so that the R-curve could be numerically predicted only from those properties. Crack growth tests using 3-point bend specimens with a fatigue pre-crack are conducted for two steels that have different ductile crack growth resistance, whereas both steels have the same mechanical properties in terms of strength and work hardening. Observation of crack growth behaviors provides that different mechanisms between ductile crack initiation from fatigue pre-crack and subsequent growth process can be applied. It is shown that two types of ductile properties of steel associated with ductile damage can mainly influence CTOD-R curve; one is a resistance of ductile crack initiation estimated with critical local strain for ductile cracking from a surface of notch root, and the other one is a stress triaxiality dependent ductility obtained with circumferentially notched round-bar specimens. The damage model for numerically simulating the R-curve is proposed taking the above two ductile properties into account, where the ductile crack initiation from crack-tip is in accordance with local strain criterion, and the subsequent crack growth triaxiality dependent damage criterion. The proposed model accurately predicts the measured different R-curves between two steels used that have the same 'strength properties', and also the stress triaxiality dependence of R-curve.

Simulation-based method for hierarchal material design to improve ductile crack growth resistance of structural component

“…According to the proposed plastic potential, the critical strain for micro-voids/micro-crack formation can be expressed by Eq. (4) as a function of stress triaxiality, which includes the material parameters a 1 and a 2 (Ohata et al 2010a). Then, the stress triaxiality dependent ductility obtained with round-bar specimens with/without circumferential notches directly provide the damage parameters a 1 and a 2 .…”

“…As the macro-scopic approach, Ohata et al (2010a) proposed ductile damage model to predict R-curve of a structural component from the information of two types of ductile properties. One is critical local strain that controls shear-slip mode ductile crack initiation from notch/crack-tip, and the other is stress triaxiality dependent ductility that controls subsequent ductile crack growth with equi-axed dimple mode.…”

“…The applicability of the proposed method was discussed by comparing experimental results for the ferrite-pearlite two-phase steel. Then, from the two types of ductile properties obtained by the meso-scopic approach, R-curve of the two-phase steel was predicted using the macro-scopic continuous damage model (Ohata et al 2010a), and its applicability was discussed.…”

“…Prediction of ductile crack growth resistance from the ductile properties obtained by the meso-scopic approach Ductile crack growth resistance curve (R-curve) of a cracked/notched component can be predicted by the macro-scopic approach proposed byOhata et al (2010a) from the mechanical properties of steel that Distributions of equivalent plastic strain, stress triaxiality and damage ratio for RVE model…”

A nonlinear cumulative evolution model for corrosion fatigue damage

“…Corrosion fatigue phenomenon is very common in marine and aerospace engineering, but there are many other issues which still do not have good solutions to this problem. With the flourish of damage mechanics (Lemaitre, 1985;Lemaitre and Chaboche, 1990;Fatemi and Vangt, 1998;Jain and Ghosh, 2008;Besson, 2010;Ohata et al, 2010), some researchers tried to study corrosion fatigue behavior of metals from the perspective of damage evolution, and proposed some corrosion fatigue damage evaluation methods (Kotsikos et al, 1999;Kermanidis et al, 2005).…”