PSI - Issue 13

Temma Sano et al. / Procedia Structural Integrity 13 (2018) 1154–1158 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig. 3 Schematics for plastic zone reconstruction using displacement data. (a) Loading condition. (b) Choosing target node and moving the node by Δ a . (c) Interpolating the displacement surround the three points. (d) Determining the displacement. (e) Giving the displacement to the target node. (f) Do (b)-(e) to all nodes.

3. Analytical results 3.1. Cyclic loading

Figure 4 shows the sets of equivalent plastic strain and hydrostatic stress distributions for different stages from loading to unloading. For mechanical simulations coupled with hydrogen effects, the equivalent strain distribution and hydrostatic stress gradient are important, because they correspond to hydrogen trap site distribution and stress driven hydrogen diffusivity, respectively. As seen here, the present analytical condition shows reasonable distributions of the two mechanical parameters even after the unloading process.

Fig. 4 Equivalent plastic strain distributions at a crack tip during loading to (a) 20 MPa √m , (b) 40 MPa √m , and (c) unloading to 0 MPa √m . Corresponding hydrostatic stress distributions during loading to (d) 20 MPa √m , (e) 40 MPa √m , and (f) unloading to 0 MPa √m . 3.2. Plastic zone evolution with hydrogen diffusion Figure 5 shows the plastic zone shapes and sizes without and with the effect of hydrogen. As reported previously, the plastic zone size is decreased by the introduction of hydrogen, which corresponds to the effect of hydrogen enhanced localized plasticity (Sasaki 2015). Hence, the present analytical model enables the characterization of both cyclic loading and hydrogen diffusion effects. Therefore, crack propagation simulation can be realized with the present model; we expect that the simulation of fatigue crack propagation under the influence of hydrogen is achieved. In the next section, we present the applicability of our proposed method for crack propagation.