Design And Finite Element Simulation Of Mechanical Properties Of In-situ Nano Aluminum Matrix Composites For Automotive Body

With the increasingly prominent of energy and environmental issues,energy conservation and consumption reduction have become the main problems for the development of autos.Eighty-five percent of fuel consumption is used for the weight of auto,and the mass of body accounts for about forty percent of total mass,therefore,the implementation of lightweight body is the most direct and effective way to save energy and reduce emissions.Nanoparticle reinforced aluminum matrix composites prepared via in-situ synthesis method have expansive application prospects in the field of body materials due to their high specific strength,specific modulus and excellent toughness.However,the in-situ nanoparticle reinforced aluminum matrix composite is a kind of multi-phase and multi-scale material and the effect factors of mechanical properties are complex,which make it difficult to design and prepare via experiment.Therefore,this paper established macroscopic mathematical models and microscopic finite element models for the mechanical properties of the in-situ nanoparticle reinforced aluminum matrix composites.Combining with the prediction results of the model,the corresponding composites were designed and prepared,and the mechanical properties were studied,and thus the cause of the deviation between the experimental value and the predicted value was determined and the models were optimized.Meanwhile,the finite element simulation of the uniaxial tension process was carried out and the stress-strain response and stress-strain field distribution were studied to illustrate the characteristics of microscopic deformation and simulate the relationship between microstructure and performance.The specific research contents and conclusions are as follows:Macroscopic models of mechanical properties of in-situ nanoparticles reinforced aluminum matrix composites were established.The elastic modulus of in-situ nanoparticle ZrB₂/AA6111composites was predicted by different models and compared with the experimental values.The results show that the predicted values of all models increase with the increase of particle volume fraction.When predicting elastic modulus by Hashin-Shrikman model,particle volume fraction must not be less than E_m/2E_p,so it is not suitable for in-situ nanoparticle reinforced aluminum matrix composites.The predicted value of Halpin-Tsai model is consistent with experimental value and the maximum deviation does not exceed 3%which is so precise.A compound strengthening model of yield strength of composite was established via linearly coupling four enhancement increments of fine grain strengthening,thermal mismatch strengthening,Orowan strengthening and load-bearing strengthening to predict the yield strength of in-situ nanoparticle ZrB₂/AA6111 composite and be compared with the experimental values.The results show that both the predicted and experimental values increase with the increase of particle volume fraction,and decrease with the increase of particle size,but the difference?60 MPa²40 MPa?is larger.By coupling the micro-fracture mechanism with the macro-fracture properties and correlating with the elastic modulus model,the fracture toughness model of the composite is established.The fracture toughness of the in-situ nano-ZrB₂/AA6111 composite is predicted and compared with the experimental values.The predicted and experimental values of fracture toughness decrease with the increase of particle volume fraction.The deviation between the predicted value and the experimental value increases rapidly with high particle volume fraction,indicating that the composite is prone to fracture failure at low strain.A finite element model of in-situ nanoparticle reinforced aluminum matrix composites was established.A three-dimensional randomly distribution unit cell model containing some in-situ nanoparticles was established by ANSYS Parameter Design Language?APDL?method.The parameters of the nonlinear isotropic strengthening model were obtained by calculation,which were 104,-19,109 and 11.Solid 185 and Solid 187 tetrahedral elements were used to freely mesh the matrix and reinforcement.The boundary conditions are degrees of freedom coupling constraints and displacement load is applied.The optimization of yield strength model of in-situ nanoparticles reinforced aluminum matrix composites was carried out,and the uniaxial tensile behavior was analyzed by finite element analysis.The model optimization results show that after correcting model by introducing the effective volume fraction,the deviation between the predicted value and experimental value is significantly reduced,ranging from 3 MPa to 14 MPa,which is only 1/20 of the uncorrected model.Comparing the proportion of different reinforcement increments,it has been found that the CTE enhancement increment contributes the most to the yield strength increment of the composite in this paper.The verification results of the finite element model show that the deviation between the experimental value?138.7 MPa?and the simulated value?145.6 MPa?of yield strength of the in-situ nanoparticle ZrB₂/AA6111 composite is about 5%,and the deviation of the experimental value?219 MPa?and the simulated value?221 MPa?of the tensile strength is only 0.9%,which confirms that the finite element model established in this paper is precise.The analysis results of finite element simulation show that the stress-strain response of uniaxial tension of composite is related to particle volume fraction and size,and its strength increases with the increase of particle volume fraction,but decreases with the increase of particle size.Meanwhile,it is revealed that the reinforcements cause the uneven stress-strain field distribution in composite.The high modulus reinforcing particles can bear higher loads and generate stress concentration areas around the particles,which leads to the excessive tendency of stress cracking of the part and failed.As the volume fraction of the particles increases and the particle size decreases,the stress born by the particles,the stress of the matrix between the particles,and the low strain region also increase.