Study On High Temperature Failure Of Stainless Steel Spring Based On GTN Model

Springs are widely used elastic components in various fields,and they are also extensively used in many high-temperature devices.The operating conditions and environments of springs used in engineering are quite complex,which makes it difficult to study and predict their effectiveness.There are several forms of spring failures,but the most important ones are fracture failure and stress relaxation failure.This article uses a combination of experimental and numerical simulation methods to obtain the constitutive parameters under different failure forms.Finally,related analysis and research are carried out on the two failure forms of springs.The main research content and conclusions are as follows:Based on the GTN(Gurson-Tvergraad-Needleman)micromechanical damage model,a finite element inverse calibration method was used to perform tensile fracture tests on round bar specimens at different temperatures to obtain the damage parameter values of stainless steel at 300℃,500℃,600℃,700℃,800℃ and 900℃.Temperature affects the material’s damage parameters,with higher temperatures resulting in larger values for all damage parameters except the initial pore volume fraction of the material itself.In addition,tensile tests were conducted on high-temperature stainless steel bars,and the fracture position obtained from the experiment coincided with that obtained from the finite element simulation.Stress relaxation experiments were performed on stainless steel at temperatures of 300℃,500℃,600℃ and initial loads of 100MPa,145MPa,and 190MPa to investigate the effects of temperature and initial load on stress relaxation behavior.It was found that with the increase of initial load and temperature,the relaxation amount increased,the stress relaxation rate became faster,and the material was more prone to deformation.The stress relaxation of the material is the result of the combined effect of temperature and stress.By fitting the stress relaxation curves under different conditions,the stress relaxation equation of stainless steel materials was obtained,and based on the relationship between stress relaxation and creep,the creep constitutive equation was obtained using the stress relaxation curve.Based on the obtained damage parameters and constitutive equation,Abaqus software was applied to simulate two failure modes of springs.The results show that at 300℃,the damaged position of the spring appears first at the bottom,and after being loaded to 259MPa,the cavity gradually appears and internal damage begins to occur.When the load on the stainless steel spring is less than 245MPa at high temperature,no internal damage occurs uniformly inside the spring,indicating uniform deformation.The volume fraction of cavities changes with temperature;as the temperature rises,the time for damage to occur will be advanced.The hyperbolic sine creep model is used to simulate the stress relaxation of the spring,and the stress change rate is used to describe the stress relaxation performance of the spring.The results show that the higher the temperature,the faster the stress relaxation speed.After 80 hours,the stress relaxation under different high temperatures tends to stabilize.During stress relaxation,stress is concentrated on the inner side of the spring,indicating that the inner side is more prone to damage under long-term loads and high temperatures.Finally,a prediction equation for spring stress relaxation at room temperature was established based on the Arrhenius theory equation.