13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- process. The weld was perpendicular to the applied load direction. Hence, the weld metal microstructure should be the same as that of the cruciform. Crack growth rates in the M(T) were obtained from constant amplitude load tests at R = 0.1. 4. Results and Discussion 4.1 Deformation, strain and stress Due to the secondary bending effect the panel exhibits out-of-plane deformation even the load is in-plane. Calculated stress contours show a double curvature shaped deformation Fig 2. Positive deformation on the face of the pad-up side means bending towards the pad-up side. The maximum out-of-plane displacement is just outside the pad-up area with a value of 2.5 mm (k = 0) and 2.2 mm (k = 1). The panel centre (where the crack growth path is) is also bending towards the pad-up side with smaller displacement of 1.8 mm (k = 0) and 1.5 mm (k = 1). The bending deformation shown in Fig 2 is under the applied load of 40 kN (equal to a stress of 100 MPa in the loading arm of 1.6 mm thickness). The FE model shows that bending magnitude depends on the applied stress as well as the biaxial stress ratio. Under the same y-axis applied load, uniaxial loading results in more out-of-plane deformation (k = 0, Fig. 2a) than that by equal-biaxial case (k = 1, Fig. 2b), but the bending pattern is the same and the difference in bending magnitude is small. The out-of-plane deformation and in-plane strains were calculated using both 3D solid elements and 2D shell element; calculated values agree with each other. Therefore the thin-shell elements are employed in the crack growth models to reduce the computational cost. Computed strains agree well with the measured at most of the strain gauge positions, and the computed deformation pattern agrees with that described by the distributions of the strain gauges. Fig. 2 Calculated out-of-plane deformation by 3D FE model under applied stress 100 MPa (figure showing the pad-up face): a) uniaxial load (k = 0); b) biaxial load (k = 1) 4.2 Stress intensity factors Four biaxial load ratios (k = 0, 0.5, 1, 2) were modelled at the applied stress y=100 MPa acting on the loading arm of the cross section of 250 mm width x 1.6 mm thickness. This stress level is reduced in the wider section and will be further reduced at the thicker pad-up area where the crack propagates. Calculated y in the pad-up area is about 50 MPa [21]. Cases were also modelled for k = 1, 2 at applied stress y = 50 MPa. Calculated mode I stress intensity factors (KI) at the different k
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