13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- direction at the mid-plane respectively. Figure 8. (a) Contour plot of the residual stress normal to the crack plane, (b) variation of the residual stress (σ22) with the distance in the crack growth direction Compressive residual stresses reduce the constraint level at the crack front region and tend to close the crack, and consequently, increase the fracture resistance. Figure 9 compares the load-displacement curves of the specimen with compressive residual stress field generated by 220 kN side compression with the as received specimen. Included in the figure are also comparisons between the model predictions and the experimental measurements. Again, good agreement is observed. 3. Concluding Remarks In this study, the residual stress effects on the ductile fracture behavior of the aluminum alloy 5083-H116 are investigated through a series of experiments and finite element analyses. An I1-J2-J3 dependent plasticity model is used to describe the plastic response of the materials and a damage parameter is defined as a weighted integral with respect to the effective strain, where the integrand is the reciprocal of the effective failure strain as a function of the stress triaxiality and the Lode angle. The model parameters are calibrated and validated by comparing the numerical predictions with experimental measurements. To generate residual stress fields in fracture specimens, a local out-of-plane compression approach is adopted and an experimental fixture is designed. The analysis results show that tensile residual stress not only increases the crack driving force but also raises the constraint level in crack tip region, which results in a lower fracture resistance. Compressive residual stress has the opposite effect. The numerical results, such as load-displacement curves and crack front profiles, are compared with experimental measurements and good agreements are observed, suggesting that the numerical model is capable of capturing the residual stress effect on ductile fracture resistance. (a) (b) fatigue pre-crack
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