Research On The Measurement Method Of Constitutive Relationship Inversion Of Elastoplastic Materials Based On Nano Indentation Technology

Nanoindentation technology,also known as depth-sensitive pressure-depth technology,is an advanced non-destructive testing technology that can effectively measure the mechanical properties of materials at the nanometer scale and has a very broad application prospect.The main principle of nanoindentation technology is to test the indenter in a small volume of micro/nano scale,extract the mechanical response of the material,and study the mechanical properties of the material according to the obtained loading and unloadin g response curves(load-displacement curves).With the improvement and improvement of finite element theory,the inversion measurement method based on nanoindentation technology has become a research hotspot.This method mainly obtains more mechanical performance parameters of materials by inversely analyzing the load-displacement curve.This thesis first systematically introduces the basic principles of nanoindentation technology,and analyzes the experimental devices,testing principles and mechanics theory involved.The inversion measurement method based on nanoindentation technology is described in detail.The factors affecting the experimental results are obtained by dimensional analysis method.The semi-closed measurement method of joint inversion of MATLAB and ANSYS is established,which provides theoretical and theoretical research for this thesis.Secondly,ANSYS was used to establish an indentation experimental model of elastoplastic material and introduce indentation contour information into the inversion measurement.The two-dimensional and three-dimensional geometric models of spherical and conical indenters were established,and the numerical simulation of the nanoindentation experiment process was carried out.The numerical simulation data were compared with the experimental data to verify the validity of the numerical model.The influence of experimental factors on the convex and concave phenomena around the indentation morphology,and the law of the occurrence of protrusions and depressions around the indentation morphology under the action of spherical and conical indenters;inversion based on nanoindentation technique In this thesis,the indentation contour information is introduced to improve the measurement accuracy of the material constitutive relation.It is proved by examples that the introduction of the indentation contour information can improve the accuracy of the material constitutive relationship inversion measurement.Thirdly,a multi-algorithm joint optimization strategy is proposed.The principle of common optimization methods is introduced,and each optimization method is applied to the calculation of nanoindentation inversion recognition.It is found that the optimization of the objective function in the process of optimizing the inversion analysis requires a large number of iterative calculations using the optimization algorithm.A single optimization algorithm usually falls into a local solution or a long solution time due to its own defects,resulting in incorrect calculation results or computational efficiency.low.In order to solve the above problems,this thesis proposes a combination of optimization strategies for optimization algorithms,and comprehensively utilizes the characteristics of each optimization algorithm to improve the efficiency and accuracy of the inversion calculation.The example proves that the multi-algorithm joint optimization strategy proposed in this thesis can significantly improve the accuracy and efficiency of measurement results in material parameter inversion measurement,and has certain reference significance for similar inversion analysis problems in engineering.Finally,pure copper and pure tungsten were used as samples to obtain experimental data such as load-displacement curve and three-dimensional indentation morphology through nanoindentation equipment.Correspondingly,the indentation profile information is introduced into the inversion analysis method and the joint optimization strategy is applied to invert the material parameters of pure copper.The results show that the elastoplastic material constitutive inversion analysis method based on indentation experiment can be established in this thesis.Efficiently and accurately invert the nonlinear material model parameters of the sample.