Preparation And Contact Analysis Of Functionally Graded Materials

The functionally graded materials have the properties of gradient changes with spatial location,it can reduce the stress concentration caused by the material mismatch,improve the adhesive strength and the surface properties of materials,and also can provide protection against bad thermal and chemical environment.The functionally graded materials have become a hot research field because of the unique properties and potential research space.In addition,the functionally graded materials used for coating can improve the contact distortion of the contact surface and inhibit the contact damage and destruction,therefore,the contact mechanics of functionally graded materials have became an important research topic.In this paper,firstly,the gradient material of aluminum alumina was prepared by hot pressing sintering method,and then we analyze and test the properties of material including the microstructure,density,compressive strength,hardness and indentation.Secondly,we conduct a finite element simulation with ABAQUS for contact mechanical,as well as the two-dimensional frictionless and sliding frictional contact were simulated and analyzed,then the numerical solutions obtained by above simulation are compared with the analytical solution and the analysis of the influence of model thickness and friction force on the contact stress is presented.Finally,we simulate the two-dimensional frictionless contact upon the gradient coating(Al/Al2O3)half plane,at the same time,the numerical solution is compared with the theoretical analysis,then we analyze the effect of elastic modulus ratio Eo/Eh of gradient coating,different function forms and gradient index n on the contact stress,and the contact curves of force?mark and force?contact area under the cylindrical punch are clearly presented.The results show that:(1)The hot pressing sintering method can prepare the gradient materials with small density,light weight and compact structure,and the gradient material not only has high compression strength,but also present a good ductility.(2)According to Webster Hardness and indentation test,it shows that the hardness of the gradient materials significantly greater than the homogeneous materials with the same loads,and with the increase of alumina content,it can improve the hardness of Al/Al2O3 materials,while this performance still is able to maintain in graded materials.(3)For the simulation of frictionless contact of homogeneous materials,when the normal load is constant,the departure from the analytical solution increases with the decrease of the layer thickness.(4)For the simulation of sliding frictional contact of homogeneous materials,the friction coefficient has a little effect on normal contact stress distributions,but there has a great effect on the in-plane tensile stress distributions,and the maximum tensile stress at the leading end increases with the increase of friction coefficient.(5)For the simulation of the semi-plane of the gradient coating,the thickness of the gradient layer is divided into 10 layers to ensure the accuracy.In the exponential model,the numerical solution is in good agreement with the theoretical value,therefore,this model can be used to analyze the frictional contact problem of functionally graded material whose parameters have a continuous change in the forms of arbitrary function.(6)The distributions of the contact stress can be changed by adjusting the gradient of the parameters of the coating materials.In particular,with the decrease of the young's modulus of the coating surface,the maximum value of the in-plane tensile stress at both ends of the contact area decreases,which is shown that the surface crack can be suppressed by adjusting the gradient of the coating and hence resist the contact damage caused by sliding and fretting.(7)The relationship between force and indentation is affected by the gradient of elastic modulus of the coating,which indicates that the gradient of the material parameters can be measured by the indentation test.