Constitutive Modeling Of Materials And Simulation Of Size Effect In Micro-cutting Process

Micro-cutting has been widely applied in manufacturing micro-parts, due to its goodadaptability and high productivity. Micro-cutting is not simply the scaled-down version of theusual one. It is marked with size effect, one of its distinctive features, which means the shearspecific energy grows up nonlinearly with the depth of cutting down. Size effect hasimportant influences on cutting force, energy dissipation and tool wear et al. None of currentconstitutive models incorporates the characteristic scale of materials, which makes itimpossible to describe correctly the mechanical behavior of materials in micro-cutting process.It is necessary to establish a model which can both incorporate size effect and connect themicro-and macro-cutting processes.A constitutive model, aimed at Al7075is developed using strain gradient plasticity theoryin this thesis, which is based on Johnson-Cook model. There are ten constants to define, forwhich, a series of experiments have been developed and implemented. The procedure ofdefinition is elaborated, too.Two kinds of user subroutines, isotropic hardening and mixed hardening respectively, aredeveloped to define material behavior based on the FEA software Abaqus/Explicit. Initialtesting on a single-element model with prescribed traction loading is carried out before theimplementation of the constitutive model.A series of simulations of micro orthogonal cutting have been launched. It turns out that(i) Stress is growing up with the depth of cutting down;(ii) The stress-strain curve is tendingtowards the Johnson-Cook model as the depth of cutting increases. Accordingly, it isconcluded that (i)The constitutive model established could reflect the size effect correctly inmicro-cutting process;(ii) The model is applicable both in micro-and macro-cutting process.The fact that the mixed hardening model incorporates isotropic coefficient, which determinesthe influence of isotropic hardening on the total hardening mode, may be more objective indescribing the hardening of materials.