Research On The Measurement Method Of Constitutive Relationship Inversion Of Elastic-Viscoplastic Materials Based On Nano Indentation Technology

Nanoindentation technology is an advanced micro/nanoscale mechanical testing technology,which has the advantages of simple sample preparation,easy operation,ganghigh test displacement and high load resolution.With the continuous improvement of its related theories and the deepening of practical research,the method of using nano-indentation technology to invert and calculate the mechanical parameters of materials has become a research hotspot.However,the coupling between material parameters,and the sensitivity of the head shape to the measured material have a great impact on the inversion measurement results.Therefore,how to improve the precision of inversion measurement and ensure the reliability of measurement results have important research significance and practical value.This study introduces the composition and working principle of the nano-indentation test system,and lists several commonly used nano-indentation instruments currently on the market.The related theories and methods of nanoindentation testing technology are introduced in detail,and the theoretical formulas involved are briefly explained.At the same time,four kinds of indenter shapes commonly used in experimental measurement are introduced,and their geometric parameters,characteristics and application scope are summarized.The elastic-viscoplastic material constitutive model is established by using inversion analysis method to identify the parameters of elastic-viscoplastic material.The nanometer indentation process was numerically simulated by ANSYS finite element software,and the elasto-viscoplastic material parameters were analyzed and calculated by the inversion identification model j ointly established by ANSYS and MATLAB,and the coupling phenomenon between viscous parameters and plastic parameters encountered in the inversion calculation process is analyzed.Multiple cyclic loading can reduce the influence of coupling action between material parameters on inversion results,which improves the reliability and accuracy of inversion measurement results to a certain extent.This paper studies the advantages and disadvantages of several common gradient-type optimization algorithms and intelligent optimization algorithms in the inversion and identification of material parameters,and proposes an improved optimization algorithm based on the characteristics of various algorithms.Moreover,an example is given to verify that the proposed algorithm has obvious improvement in inversion accuracy and computing efficiency compared with other algorithms.Then using the experiment measuring the commonly used four head shape on the elastic viscoplastic material parameters were analyzed,and the study of different head shapes on the sensitivity of the material parameters,and according to the size of the sensitive degree of classification,providing reliability reference for proper selection of medium pressure head for material parameter inversion measurement and ensuring the accuracy of inversion measurement results.Three kinds of elastic-viscoplastic metal materials,namely titanium alloy,pure copper and pure aluminum,were selected to conduct nano indentation experiment,and the methods of primary loading,secondary cyclic loading and three cyclic loading were adopted to test them.The experimental results are analyzed to verify the effectiveness of multiple cyclic loading methods for parameter decoupling.