Crystal Plasticity Study On Bending Deformation Behavior Of Ultra-fine Grained Aluminum Alloy

Ultra-fine aluminum alloy has high strength and stress fatigue properties,and has great potential applications in aerospace,medical,electronic communication and other fields,such as micro-screws,micro-gears and artificial limbs in MEMS.These components in the service process,often under eccentric compression load bending effect,or directly under bending load,in order to secure the security of their service to understand and master the monotonic bending and bending fatigue deformation behavior,especially in the analysis of the deformation mechanism of microstructure scales,it is extremely necessary and urgent.In this paper,three-point bending numerical simulation of ultra-fine grained aluminum alloy is carried out based on crystal plasticity theory and sub-model method,then verified by digital image correlation method(DIC)experiment,and then the formation and influencing factors of shear band during deformation are studied,then the bending fatigue behavior of ultra-fine grained aluminum alloy is simulated,and the relationship between microstructure and fatigue failure is analyzed.Finally,based on the accumulative slip on the slip system,a fatigue indicator parameter D^?is proposed to predict the fatigue crack initiation location,which is verified by the classical fatigue indicator method of accumulative plastic slip and accumulative strain energy dissipation.The main research results of this paper are as follows:1.Three-point bending finite element model was established based on the crystal cyclic plastic constitutive model,the Chaboche combined hardening cycle constitutive model and the sub-model method.Considering the microstructure and mechanical properties of the ultra-fine grain aluminum alloy,the material constitutive parameters of the ultra-fine grain aluminum alloy were fitted by trial-and-error method combined with the experimental data.The results show that the mechanical behavior of the three-point bending of ultra-fine aluminum alloy can be simulated well by the combined macroscopic and mesoscopic submodel method.2.The study of monotone three-point bending shows that:(1)The variation of loading rate and load has a great influence on the formation of shear band.With the increase of loading rate and load,the bands of shear band will increase,and the length will also increase,and the degree of strain localization will become more concentrated.(2)By constructing three typical texture models of"Goss","S"and"Cube",the influence of texture composition on the development of shear band in the bending deformation process was studied.The results show that both"Goss"texture and"S"texture can promote the formation of shear bands,while"Cube"texture can inhibit the development of shear bands.3.In order to study the relationship between microstructure and fatigue failure,three point bending fatigue numerical simulation of ultra-fine aluminum alloy was carried out,and the cumulative slip on the slip system was compared and analyzed.Considering that the primary slip system leads the initiation of fatigue cracks and the contribution of all slip systems to fatigue cracks,a fatigue indicator D₁ represents the cumulative slip along the primary slip system and another fatigue indicator D₂ represents the total cumulative slip along all slip systems.The interaction between the two factors is represented by the product of the two factors.A fatigue indicator D^?was established to predict the location of crack initiation.Finally,the prediction results were verified by the classical accumulative plastic slip P_cyc method and accumulative strain energy W method.The results show that the established fatigue indicator D^?can accurately predict the location of crack initiation.