Research On Material Micro-nano Indentation Hardness Measurement Simulation

Following the development of micro-nano machining technique and the application of micro-parts, the measurement and evaluation technique of micro-parts'surfacial mechanical property have become a key in the machining process. Hardness is a simple and efficient means in the micro-nano dimensional surface property measurement. Macroscopical hardness measurement is limited by the testing system resolution and can not satisfy the microcosmic demands. Therefore, test and evaluation techniques for indentation hardness have significant academic value and actual significance. Under micro-nano dimension, the load-depth curve is affected by the indenter shapes, inhomogeneity of material property and the systematic error, etc., it is unable to appraise and calculate the real hardness value of the material. Adopting the simulation analysis of indentation course can neglect the influence factors that can't be dispelled in the experiment. And it offers important basis for finding the factor, which influences the hardness calculation and leads to the hardness indentation size effect. So the study for the measurement and evaluation of micro-nano dimension hardness technology has important theory value and realistic meaning.Based on the analysis of the indentation hardness testing process, a finite element method (FEM) simulation of the indentation process is designed and a FEM simulation model established. The model is achieved by setting material property in accordance with the plasticity of pure Al and locating boundary conditions and applying load of indenter on the basis of real indentation experiment. Operating the FEM simulation post-processing and the ABAQUS secondary development to output indentation load-depth curve and indentation surface data, provide basis for the application of hardness calculations.Based on FEM indentation experiments, expand the theoretical study of the different indentation hardness calculated method. Caculating hardness achieved by Oliver-Pharr method and by area and volume of indentation. According to anylasying the different hardness calculation methods under each indentation depth, the FEM simulation indentation experiments calculated hardness results are consistent with the real indentation experiments, so it is proved that the reasonable of FEM indentation. Because of the indentation pile-up, lead to Oliver-Pharr method calculated hardness values are relatively large, the methods of direct area and the volume hardness are more closer to the true hardness of material, the volume hardness method is more stable.Based on FEM indentation experiments, expand the study of factors of radius of indenter tip, friction coefficient between the indenter and the substrate and the verticality of indenter, the results show that the volume hardness value changes gentlest, little influence by the radius of indenter tip, friction coefficient between the indenter and the substrate, the verticality of indenter, elastic recovery, pile-up and sink-in, etc..Expand indenter radius effects on the hardness of the theoretical analysis, the FEM simulation indentation experiments calculated hardness results are consistent with the real indentation experiments, verified by FEM indentation experiments. By reducing the size of model and the grid refinement can improve the accuracy of FEM indentation hardness when the indentation depth is small. By re-setting the boundary conditions of FEM indentation model, hardness calculation errors can be reduced in the large indentation depth.