Empirical Analysis Of Stress Relaxation Model Based On Steady-state Creep Equation

Creep and stress relaxation are the inherent mechanical properties of viscoelastic materials.The research and prediction of material creep and stress relaxation not only enable us to correctly understand the failure mechanism of viscoelastic materials in long-term service,but also provide a new idea for the designing,processing and application of viscoelastic materials.This paper describes the stress relaxation behavior of several metal and polymer materials by using the stress relaxation model based on the steady-state creep equation,and analyzes their creep and stress relaxation mechanisms.On this basis,a new steadystate creep mechanism conjecture was proposed,and the conjecture was empirically analyzed by designing stress relaxation experiments.The specific research content and results are as follows:(1)The relationship between stress relaxation parameters and creep mechanisms is analyzed by fitting and analyzing the stress relaxation curves of AA7150-T7751 alloy,Babbitt metal ZCh Sn Sb11-6 and beryllium bronze C17500,and comparing with other researchers' studies on the creep and relaxation mechanism of this materials.The results show that the stress relaxation model based on the steady-state creep equation has a good fitting effect on several metals,and the fitting correlation coefficients are all greater than 0.99.The stress relaxation rate increases and the stress relaxation parameters(steady-state creep rate index m and characteristic relaxation time logarithm lg?)show a downward trend with the test temperature or initial stress increases.Stress relaxation is the result of the gradual superposition of the deformation of the microelements of each material during the relaxation process.(2)The stress relaxation test data of polymer materials fitted and analyzed by using the new stress relaxation model,choosing polyethylene and polyurethane,and the influence of test conditions changes on the stress relaxation parameters is analyzed.And the relationship between the change of the creep deformation mechanism and the stress relaxation parameters is analyzed during the stress relaxation process.The results show that the goodness of fit of the stress relaxation model based on the steady-creep equation for polyethylene and polyurethane materials is greater than 0.97.The relaxation process of non-crosslinked polymers is actually the result of the relaxation and superposition of various moving units,and the stress relaxation parameters decrease steadily as the temperature rises.Due to the existence of cross-linking points,the cross-linked polymer does not produce a displacement of the center of mass of the molecular chain,and can only gradually relax to a certain value.The stress relaxation parameter increases temporarily with the increase of temperature,and then continues to decrease.(3)Based on the derivation of the aforementioned creep mechanism of metal and polymer materials and the stress relaxation model based on the steady-creep equation,a new steady-state creep theory conjecture is proposed.And the stress relaxation test of the multiple measuring-point and multi-sample composite system is designed to determine the stress relaxation performance of the composite system and the components in the system.The new model is used to analyze the stress relaxation parameters of the composite system and each component,and the steady-state creep mechanism conjecture is proof analyzed.The results show that the stress relaxation results of the multiple measuring-point and multi-sample composite systems and each component of this system can be described by the stress relaxation model based on the steady-state creep equation,and the stress relaxation parameters of the composite system are between the values of the stress relaxation parameters of each component.The stress relaxation parameters of each component are related to the elastic modulus of the component.There are obvious differences in the suspension parameters among the components of the tandem composite system.The reciprocal of the steady-state creep rate index m of the series composite system is equal to the product of the reciprocal of the m value of each component in the system and the volume fraction of the system.The goodness of fit between the theoretical value and the experimental value is 0.98.The stress relaxation result of the parallel composite system is similar to the stress relaxation result of the largest component in the system.The steady-state creep rate index m of the parallel composite system is equal to the product of the m value of each component in the system and the volume fraction of the system,and the goodness of fit between the theoretical value and the experimental value is 0.9975.The overall relaxation characteristics of the viscoelastic material are the result of the superposition of stress relaxation among the components of the material during the relaxation process.