13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- Figure 6. Contour plots of the residual stress normal to the crack plane: (a) 220 kN side-compression, (b) 182 kN side-compression (stress unit in contour plots: psi) Figure 7. Comparisons of the computed and measured load-displacement curves for C(T) specimen without residual stress and with tensile residual stress After the residual stress fields have been generated in the specimens, finite element analyses of the compact tension tests of these specimens are carried out. Figure 7 compares the model predicted load-displacement curves with experimental records for the as-received specimen as well as the specimens with tensile residual stress field. The numerical model captures the effect of the tensile residual stress on the fracture resistance. The existence of tensile residual stress drastically reduces the fracture resistance and lowers the specimen’s load carrying capacity. After crack grows away from the residual stress influence area, the features of crack growth become similar to those exhibited by the virgin specimen. 4.3. Fracture tests with compressive residual stress When side-compression is applied behind the crack tip, crack will close and the crack surfaces will contact each other. In finite element analysis, to prevent crack surface penetration, a rigid surface is added to the symmetric plane behind the crack tip. The finite element analysis results show that the high compressive residual stress region is at the initial EDM notch (behind the fatigue pre-crack front) and the residual stress distribution is not as uniform as tensile residual stress case, Figure 8(a). Figure 8(b) shows the variation of the residual stress (σ22) with the distance in the crack growth (a) (b) as-received 182 kN LOPC 220 kN LOPC
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