Indentation Testing Method To Obtain Uniaxial Constitutive Relationships Of Materials

Material consititutive relationships of small dimensional components and welding structures for safe control of key engineerings are very important, and up to now it is hardly valid to obtain them by the traditional monotonic tensional tests. Indentation method is a small-invasive test method, which has hopeful prospect in the estimation on the mechanics properties of small-scale samples and in-service engineering components. This thesis investigates the indentation method used to determinate uniaxial consititutive relationships of metallic materials based on finite element simulation and experimental verification. Some research results are given as followed:(1) On the basis of prepressing hardening, an improved indentation method used to accurately determinate elastic modulus of materials is proposed. For304stainless steel and T225NG alloy, expriments show that the accuracy of elastic modulus obtained by the new method is evidently higher than the results of single-cone-indenter indentation method.(2) With the finite element simulation, a method to obtain constitutive relationships of materials based on energy method of indentation (CR-EMI) corresponding to cone indenter with60degrees to determinate material constitutive relationship is proposed, in which a represented stress σr is regarded as intermediate variable. According to the linear relationship between nominal hardness H and Brinell hardness Hb, a method to obtain hardness of materials based on energy method of indentation (H-EMI method)by using constitutive relationships of materials is developed.(3) Due to the power law between the parameters in Hollomon constitutive relationship model and indentation energy ratio We/Wt, new CR-EMI-H(Hollomon) method to determate material constitutive relationships and H-EMI-H(Hollomon) method to get Brinell hardness corresponding to the curve of indentation load-endintation depth of60degree and70.3degree are developed, respectively.(4) Power law relationships between indentation energy ratio Wt/We and the Hollomon parameters for different Brinell hardness scales are given, then a spherical indentation method to determinate material constitutive relationships is developed.(5) Based on indentation and hardness tests on eight engineering materials, the validity and precision of above-mentioned indentation methods are certified.(6) On the basis of CAT principle and the developed indentation methods, the technical design of an indentation equipment is suggested.