Numerical Study On The Deformation And Fatigue Behavior Of Metallic Glass

Amorphous alloy,also known as metallic glass,has the advantages of high strength,high elastic modulus and corrosion resistance,but also has poor plastic deformation ability and other shortcomings,which seriously restrict the largescale application of metallic glass.In this paper,the deformation and fatigue characteristics of metallic glass are studied by theoretical model and numerical simulation method,and the simulation results are verified by experiments.Free volume theory accounting for hydrostatic stress has been used to establish the mathematical model,study the deformation behavior of the metallic glass under fatigue loading and the notch effect and notch cluster effect of metallic glass,for the further understanding of metallic glass under complex stress deformation behavior provide further theoretical support,and beneficial to actual production and application to provide the technical guidance.The research content and main conclusions of this paper are as follows:Firstly,constitutive law considering hydrostatic stress was used to investigate the fatigue behavior under different strain amplitudes,the stress variation curves were plotted after finite element analyses.It was found that fatigue limit decreases with larger strain amplitudes,vice versa.Besides,by combining with the morphology of free volume and shear band distribution,the stress variation patterns could be interpreted well.Furthermore,within one cycle,compressive stress is higher than tensile stress,displaying an obvious hydrostatic stress effect,that is asymmetry of tensile and compressive strength.The relation of fatigue limit and strain amplitudes demonstrated that fatigue life decreases sharply with larger strain amplitude.Secondly,Finite Element Model was utilized to analyze the notch effect on the global strength and plasticity of metallic glasses.By comparing with experimental results,current simulated results and simulations obtained by other models,it was concluded that current results could achieve better precision in describing the correlation of yield strength and different settings of notches.Based on the free volume and shear banding patterns by the FEM,it was found that specimens with two symmetrical notches could possess higher strength and plasticity,which was caused by the intersection of two major shear bands during deformation process.This pattern will not result in the fast fracture along one shear band so that the plasticity was improved obviously.Besides,by comparing with the results under both tension and compression,the asymmetry of tensile and compressive yield strength was also found for notched samples.That is because that the compressive hydrostatic stress could induce shrink effect,which could lead to higher compressive yield strength than tensile strength.Besides,simulations revealed that the aspect ratio of specimen has slight effect on the samples with two symmetrical notches.Thirdly,by using the same constitutive laws,effect of notch cluster was investigated to understand its influence on global strength and plasticity.Results demonstrated that the sample with H=6R displayed the best plastic deformation abilities when only changing the vertical distance of notch cluster.According to the simulated shear band morphology,the plasticity enhancement could be ascribed to the shear band intersection which hinder the fast propagation process within sample.Furthermore,when changing the notch width w,it was found that W=2R and H=6R is the optimized configuration to obtain the best plasticity.Therefore,this design could provide a technical support in order to fabricate porous metallic glasses with high strength and plasticity.Fourthly,the effect of critical dimensional deviation on notch cluster effect of metallic glass is studied.The results show that when the size deviation is less than 5%,the gap radius,the vertical center distance between the notches,the horizontal width between the notches and other key size deviations have no significant effect on the metal glass notch cluster effect,and it is reliable to optimize the plasticity of metal glass through the notch cluster effect in engineering application.The overall stiffness of samples with dimensional deviation is almost unchanged,while the yield strength decreases slightly.In particular,the yield strength of metallic glass samples is improved when the deviation of single notch radius is up and down and the deviation of single notch vertical center distance is up.The yield strength decreases monotonically with the increase of the deviation,but the absolute value is not large,when the deviation of the double notch radius,the deviation of the distance from the center of the notch on one side and the horizontal width between the notch and the deviation of the distance from the center of the notch on both sides is taken.To sum up,the study in this paper further improves the theoretical basis of numerical simulation analysis of metallic glass deformation and fatigue,which is of great significance to promote the large-scale application of metallic glass.