13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Table 1. Mechanical properties of steels used. !0.2 !T YR "T Steel A 620 721 0.86 8.5 Steel B 650 735 0.88 5.1 Steel C 829 879 0.94 5.8 !0.2 : 0.2%proof stress, !T : Tensile strength, "T : Uniform elongation (G.L.=32mm), YR : Yield to tensile ratio !0.2/!T) Figure 2. True stress-true strain curves for steels used. Figure 3. Ductile properties controlling ductile crack growth resistance for steels A, B and C. 2.2. Simulation based prediction of ductile crack growth resistance 2.2.1. Simulation model for ductile crack growth behavior [1] The damage model for numerically simulating a ductile crack growth resistance, that is R-curve, has been proposed taking the two ductile properties of steel 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 details of the criteria are described in the literature [1] The local strain criterion is applied only for predicting ductile crack initiation from tip of a crack-like defect. In the FE-model, a first element ahead of crack-tip losses a stiffness when an equivalent plastic strain at this element !p tip attains to a critical local strain (!p tip) cr of steel of interest. The triaxiality dependent damage criterion is applied for simulating subsequent ductile crack extension. The proposed yield function, that is the plastic potential, as a function of the damage variable D* is expressed in Eq. (1), != " # ! " # $ % & 2 +a1D'exp a 2 !m " ! " # $ % &(1=0 (1) where ! and !mare macroscopic equivalent stress and hydrostatic stress of the unit cell, respectively, and ! is flow stress of a matrix material. This yield function, which is based on a 0 200 400 600 800 1000 0 1 2 3 4 5 Steel A Steel B True stress, s=P/A (MPa) True strain, e=ln(L/L0) (%) Steel C Round-bar tension test 0.0 0.5 1.0 1.5 2.0 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Equivalent plastic strain, !p Stress triaxiality, "m/" Steel B Steel A Steel C
RkJQdWJsaXNoZXIy MjM0NDE=