Fatigue crack propagation behavior analysis of 15MnTi steel based on cyclic cohesion model

Abstract

15MnTi steel is widely used in high load structures such as bridges, pressure vessels, ships, and vehicles due to its excellent mechanical properties. In the course of service, the failure of steel structure is mostly caused by fatigue fracture. In order to investigate the crack growth of 15MnTi steel under fatigue load, the cohesive zone model (CZM) was used to simulate the crack growth. The CZM can simulate brittle and plastic fracture behavior by using the function of crack interface opening force and opening displacement to avoid the stress singularity of crack tip. On this basis, a cyclic cohesive zone model (CCZM) was established to study the fatigue crack propagation behavior. This model effectively links damage, tractive force, and cumulative displacement while incorporating the process of fatigue crack growth to accurately simulate material damage evolution under fatigue load. Experimental studies on crack growth in 15MnTi steel at three stress ratios reveal a linear relationship between crack growth rate and stress intensity factor range for different stress ratios. The parameters of Paris formula were calculated using crack growth rate and stress intensity factor range, which provided reference for the selection of model parameters. By utilizing the user element subroutine (UEL) in Abaqus and compiling the CCZM using Fortran language specifically for 15MnTi steel, simulations were conducted to analyze the evolution of crack tip state under various stress ratios and discuss the corresponding crack growth behavior based on experimental observations. The results demonstrate that the fatigue crack propagation rate varies linearly with both stress ratio range and stress intensity factor range, consistent with experimental findings. The results of the opening and closing evolution of the crack tip are consistent with the law of crack propagation, which indicates that the plastic behavior of the crack tip can be effectively characterized by the CCZM. Furthermore, parameters obtained from the cyclic cohesive zone model's Paris formula closely match experimental data, thus validating its accuracy and feasibility in simulating fatigue crack propagation behavior.

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