Energy Dissipation Analysis Of Fatigue Crack Propagation Of 15MnTi Steel Based On Cyclic Cohesive Zone Model

15MnTi steel has excellent mechanical properties such as high toughness,good wear resistance,corrosion resistance and high temperature resistance,and is widely used in bridges,pressure vessels,ships and vehicles in high-load structures.Most of the failure of mechanical structure is caused by fatigue fracture in key parts,and during manufacturing,transportation and service,due to inevitable external factors,it will cause minor defects in components,and with the continuous development of fatigue load,eventually cause structural fracture and failure due to fatigue,which may cause immeasurable disasters and bring huge economic losses.There must be conversion between various forms of energy in the process of fatigue crack propagation,and clarifying the energy conversion mechanism can essentially reveal the fatigue crack propagation mechanism,which is of great significance for the health monitoring and remaining life evaluation of crack-containing structures.In this paper,the fatigue crack growth parameters of 15 MnTi steel are determined by crack growth test,and the energy dissipation in the fatigue crack growth process of 15 MnTi steel is studied by using the cyclic cohesive zone model subprogram compiled by the finite element software ABAQUS and Fortran language,and the effects of heat convection and thermal radiation on energy dissipation in the crack growth process are analyzed,the main contents are as follows:(1)Through fatigue crack growth experiment,the a-N curve of the material under three stress ratios is obtained,and the da/d N curve function of the material is further fitted under the double logarithmic coordinate system,and finally the fatigue crack growth Paris formula and stress intensity factor threshold value of the 15 MnTi steel material are given.(2)Based on the cohesive unit algorithm,the ABAQUS UEL subprogram suitable for fatigue crack growth analysis of 15 MnTi steel materials was compiled in Fortran language,and fatigue crack growth analysis was carried out on 15 MnTi steel materials in combination with the fatigue crack growth parameters obtained by the test.The unit stiffness,crack tip state evolution process,and damage distribution state of the model under different stress ratios were discussed,and the fatigue crack growth parameters obtained by fatigue crack growth test were compared,which verified the feasibility and accuracy of applying cyclic cohesive zone model to analyze fatigue crack growth law.(3)The ABAQUS displacement-temperature coupling analysis method was used to convert the plastic properties of materials under cyclic load into thermal energy,and the temperature field and energy dissipation evolution of the finite element model were simulated and analyzed,and the temperature field evolution law of the material under cyclic load was given.The results show that the overall plastic dissipation energy,the plastic dissipation energy per cycle and the range of stress intensity factors of the crack tip of the model are bilogarithmic linear.The temperature rise of the crack tip has a power function relationship with the crack growth rate and stress intensity factor range.(4)Considering the surrounding environmental influence,the temperature field and energy dissipation of 15 MnTi steel materials under different convection coefficients and thermal radiation coefficients under different convection coefficients and thermal radiation coefficients were obtained,and the results showed that convection and radiation had an effect on the energy dissipation in fatigue crack propagation and could not be ignored.