Experimental Study On Indentation Response Of Material Under Pretension Force

With the continuous development of materials,new types of materials and various aloys have been continuously developed,and there are more and more ways to measure the mechanical properties of materials.On the basis of the traditional measurement of mechanical properties,a new type of nanoindentation technology has been applied more and more.In this paper,based on the pure nanoindentation test,pre-stretching conditions were added,and the tests and finite element simulations were carried out on the 45-gauge steel and 7049-alumina pre-stretched and pre-stretched conditions.The analysis is intended to explore the influence of pre-stretching on the mechanical properties of the material.The thesis firstly combs the development of mechanical performance testing instruments at home and abroad,including the traditional mechanical performance testing and its instruments,the corresponding simulation analysis of indentation and the development of its instrumentation.Secondly,the paper expounds the relevant principles of nanoindentation test system and how to carry out the test of material indentation response under pre-stretch conditions,and introduces the test device.Based on this,the paper describes in detail the nano indentation test on 45 steel and 7049 aluminum.The displacement-load curve was measured by a large number of repetitive tests.Then,pre-stretching conditions were added and the material was subjected to nano-indentation test,and the pre-stretching conditions were continuously increased.By comparing the experimental data,it is found that as the pre-stretching conditions are added and increased,the entire indentation curve is shifted to the left,that is,after the same indentation load is loaded,the maximum indentation depth is reduced,and the residual depth is also reduced.Small,hardness and elastic modulus increase.Although the rates of hardness and elastic modulus increase are different,they still maintain an increasing trend for two different materials.Finally,in this paper,choosed ABAQUS finite element bionic software to synchronously simulate the actual experimental content,observe the stress cloud diagram of the material in nanoindentation,and compare the displacement-load curve of nanoindentation under different conditions.The simulation results are consistent with the conclusions from the nanoindentation test.Comparing the simulation results with the experimental results,it is found that there are some differences between the curvature and the smoothness of the loading part of the displacement-load curve.After summarizing the analysis,it is considered that this is due to the material parameters,boundary conditions,simulation meshes,and the actual test and simulation analysis.The actual test conditions and other environmental conditions caused.However,in the conclusion,the results obtained from the actual tests are consistent with the results obtained from the simulation analysis,and the two have been mutually authenticated.Through the experiments and simulations,it can be found that pre-stretching will make the material similar to work hardening process,the entire displacement-load curve to the left,the material's hardness elastic modulus increases.After increasing prestretching conditions,this trend also increases.It can be seen that the mechanical properties of the material will change under different pre-stretching conditions.