Research On Mechanical Properties And Simulation Of Gaphene/Al Composites

In this paper, effects of the graphene and porosity on the mechanical property of Graphene/Al composites are investigated by both the experimental preparation and finite element simulation respectively. In the experiment, two-step method, namely, alcohol dispersion and ball-milling was applied to prepare uniform graphene/Al powder, and then graphene/Al composites with 0.5vol%、1vol% and 2vol% graphene were fabricated by vacuum powder metallurgy method. The morphology of composite powders was studied by SEM, meantime, the microstructure and mechanical properties of graphene/Al composites were analyzed by SEM, OM, XRD, Electronic universal testing machine and micro Vickers hardness tester respectively. Effect of volume fraction of graphene, size, distribution pattern and morphology of graphene and the porosity, pore size and pore shape on mechanical behavior of graphene/Al composites were simulated by finite element method. At last, the simulation prediction and the experimental results were also comparatively studied.The experimental results showed that the graphene uniformly mixed with Al powder by two-step method, and graphene/Al composites prepared are compact and graphene nanosheets were uniformly distributed and embedded in the aluminum matrix. Graphene/Al composites are oxidized slightly and present th characteristic of ductile fracture, meantime the brittle phase such as Al2O3 and Al4C3 were not found in composites. It was found that the volume fraction of graphene has important influence on the mechanical properties of composites. The tensile strength, compressive strength and microhardness of graphene/Al composites increase with increasing of graphene volume fraction. When the volume fraction of graphene increases from 0.5% to 2%, the tensile strength of composites increases 139 MPa to 215 MPa. The compressive strength increases from 297.35 MPa to 647.34 MPa, and the microhardness increases from 72 HV to 85.62 HV. When the graphene volume fraction is 1%, composites not only have high tensile strength, but also have good pasticity, and it present good mechanic properties.The two-single-cell numerical model was applied to simulate the different stress and strain field of composites under the uniaxial tensile conditions. The simulation results show that the stress of reinforcement which is along the direction of the tensile is far higher than that of matrix. The stress concentration of matrix and large strain appear at near the top of the reinforcement, which extends along the tensile direction angle of 45°. The matrix stress and strain located in both sides of the reinforcement is less. The volume fraction, size, distribution pattern and marphology of the reinforcement have significant influence on mechanical behavior of graphene/Al composites. With increasing of the reinforcement volume fraction, the matrix presents less stresses. The reinforcement size has important influence on dislocations strengthening, but it has little influence on enhancement of load transfer. When the relative angle between the reinforcements is 30°, the interfaces separation of composites and the cracking risk of matrix are smaller compared with other distribution pattern. When the reinforcement is cuboid, the matrix stress is larger, and large plastic deformation appears at edges and corners. The mechanical properties of composites are very poor. The matrix stress along the tensile direction which is near the porosity is smaller, while on both side of the porosity is larger. The porosity is a potential source of crack. Some factors such as porosity, porosity diameter and porosity shape have influence on the stress and strain distribution of composites. When the porosity gets higher, the porosity aggregation tendency will get easy; this will lead to material failure. With the increase of porosity diameter, the stress distribution in the matrix is not less uniform, and the large strain area of the matrix around the porosity increases. The composites contains circle porosity have a higher intensity compared with other irregular shapes porosity. Its failure mode may be porosity cracking, while the others failure mode are more inclined to interfaces separation. The simulation of the stress-strain of composites is well match with experimental results. Meantime it was also found that the finite element simulation value is bigger than experience value.