Elastoplastic Analysis Of Pressure-Sensitive Materials Related To The Size

Classical strain gradient plasticity theories are based on Mises yield criteria andcan describe well the plastic behavior of ductile metals. However they all neglectedthe influence of the volume changes on the plastic behavior of materials. Classicalstrain gradient theories cause large deviation when studying the microscale propertiesof pressure-sensitive materials whose plastic deformation is influenced by hydrostaticpressure, such as bulk metallic glasses. In this paper, numerical research work formicro-indentation response and steady-state crack growth, aiming at the effect of thepressure-sensitive materials. This paper has important guiding significance on theprediction of the plastic deformation mechanism of the material related to pressuresensitive and size effect. The main content of this paper is as follows:(1) By redefining the volumetric strain and plastic strain increments, the CMSGtheory presented by Huang was modified. The modified theory considers the effect ofhydrostatic pressure on the plastic behavior of materials. The corresponding finiteelement calculation program was developed via the user-material subroutine UMATprovided by ABAQUS.(2) The indentation response of the BMG Zr55Cu30Al10Ni5was simulatedconsidering different depths, pressure-sensitive factors, friction coefficient, and thehalf-angles of the indenter. The numerical results shows that the established CMSGtheory and the corresponding finite element calculation format can accurately describethe elastic-plastic behavior of the material such as the BMG Zr55Cu30Al10Ni5. Theestablished theory and finite element calculation format can predict well the pressuresensitive size effect of BMG Zr55Cu30Al10Ni5in micro scale. The pressure sensitivefactor can enhance the hardness, elastic recovery and the Mises stress. The extent ofelastic recovery and the plastic strain gradient obviously enhance with the increasingof the friction coefficient under small indentation depth, while the enhancement canbe neglect under large indentation depth. The large half-angle of the indenter candecrease the force, however, enhance the plastic deformation, extend the plastic zoneand weaken the pile-up underneath the indenter.(3) Mode I crack under steady-state growth and plane strain was analyzedemploying the modified CMSG theory. The results show that the stress can enhance the hydrostatic pressure and the plastic strain gradient near the crack tip. The Misesstress near the crack tip increases with the increase of the pressure sensitive factor.(4) On the basis of the flow theory of MSG plasticity for pressure-sensitivematerials presented by Lu Feng et al, the corresponding finite element calculationformat was supplemented into ABAQUS using the user-defined element (UEL)subroutine interface. The micro-indentation response of the BMG Zr55Cu30Al10Ni5was simulated. The load-depth curves and the hardness under different indentationdepths are calculated and compared to the results obtained CMSG theory, whichshows that MSG theory can obtain larger load and hardness than CMSG theory undersmall depth, while the results obtained by the two theories are gradually consistentwith the increase of the indentation depth.