The Methods And Applications Of Indentation Test For Mechanical Properties Of Materials

The Young's modulus,stress-strain relations,strength and hardness of materials are very important basic parameters for mechanical analysis,optimal design and safety evaluation of engineering structures,however,for welded structures,in-service equipment and small size materials,it is difficult to obtain the mechanical properties parameters by the traditional uniaxial tensile test method.Due to the "no sample" and "micro damage",the indentation test method can be used to test the mechanical properties of local structure or small size materials and it has been hilighted and applied into a lot of researches.In this paper,based on the previous research work,with finite element analysis and a variety of metal material tests,the indentation test method was studied,and the following work was completed:(1)Based on the classical Oliver-Pharr model and the macro indentation test,a indenter coefficient ? model was proposed to obtain the Young's modulus E,for eleven kinds of tested ductile metallic materials with spherical indentation.The Young's modulus of the material was obtained through the initial unloading stiffness S of the load-displacement curve of the single indentation test,and the comparison with the results of the uniaxial tensile test showed that the model could obtain the elastic modulus of the metal material simply and accurately.(2)Based on energy equivalent assumptions,i.e.,in the effective deformation domain of the loaded component,the strain energy density of the representative volume of the complex stress-strain state is equal to that of the uniaxial stress state RVE equivalent to the stress-strain of Von Mises,and there is an energy density center that product of the strain energy density and the effective deformation volume is equal to the external work.a semi-analytical spherical indentation(SSI)model and method of determining model parameters is proposed to describe the relation among indented load,depth,the diameter of spherical indenter and Hollomon-law parameters,then,the stress-strain relations and tensile strengths of the materials were obtained by the load-depth curves of indentation test.The model was verified by power-law material in a wide ranges of numerical values.Through indentation test of eleven ductile metal materials,the results show that the stress-strain relations and tensile strength obtained by indentation test method based on SSI model are in good agreement with the results of uniaxial tensile test.(3)Based on SSI model,a Brinell and Rockwell hardness prediction model related to Hollomon law parameters was proposed,and the Brinell and Rockwell hardness of materials could be predicted according to Hollomon law parameters.With finite element analysis,the parameters of the prediction model were determined and the model was verified within a wide range of numerical results.Eight kinds of ductile metal materials were adopted to complete the Brinell and Rockwell hardness tests.The results show that the hardness value predicted by the model is in good agreement with the test results.The methods of indentation test based on the above theoretical model can be applied to the mechanical test of materials simply and effectively.