13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- Material E(MPa) σY(MPa) Rm(MPa) K' n' σe(MPa) S460N 208000 470 682 1181 0.161 312 E is the material Young’s modulus. σY is the material yield stress. Rm is the material ultimate tensile strength. K' is the material cyclic hardening coefficient. n' is the material cyclic hardening exponent. σe is the material endurance limit. 4.1. Damage parameters analysis For the chosen material, the unknown damage parameters in the damage evolution law are just A, m and λ. The material dependent triaxiality influence coefficient λ is fixed first for λ=1.2. The decision for this parameter is based on many trial calculations and a little supposition. The recommendation λ value for material S460N ranges between 0.8 and 1.2, a change of the parameter λ will influence the other two parameters A and m. After λ is chosen, a simple simulation is applied to analyze the material dependent damage controlling parameters A and m. The finite element model consists of two plane strain elements (CPE4) connected by one cohesive element. The model is loaded by cyclic displacement, the loading ratio is R=-1. In order to reflect the real material response under cyclic loading, the material behavior for continuum element uses a nonlinear kinematic hardening model in ABAQUS. Three different ways are offered by ABAQUS to define the nonlinear kinematic hardening component, specifying the material parameters directly, specifying half-cycle test data or specifying test data from a stabilized cycle. In this paper, nonlinear kinematic hardening model is identified from the stabilized cyclic test. Series of the parameters A and m are investigated and the calculation results are plotted in the material strain-life curve, shown in Figure 3. 1 10 100 1 10 100 1000 total strain range(%) number of cycles S460N A=25,m=3.7 A=50,m=3.7 A=75,m=3.7 1 10 100 1 10 100 1000 total strain range(%) number of cycles S460N A=25,m=2.3 A=25,m=3 A=25,m=3.7 Figure 3. Effect of damage controlling parameters A and m It is obvious that the parameter m influences the slope of the strain life curve. With increasing the value of m, the slope of the strain-life curve becomes flatter. The parameter A does not influence the slope of the strain-life curve. However, it makes the curve moving parallelly. According to these rules, the parameters A and m can be identified by fitting the numerical results to the experimental strain-life curve. 4.2. Fatigue crack initiation simulation The strain-life curve of the material S460N is expressed by Equation (11)
RkJQdWJsaXNoZXIy MjM0NDE=