Viscous Behavior Of Material Deformation In Cutting Process

Cutting is a large plastic deformation process,the strain rate increases with the increase of cutting speed,and even reaches 105 s-1 in high-speed cutting.The dynamic mechanical properties of materials at high strain rate are different from those at quasi-static state,and the influence of viscous behavior on the plastic deformation process of materials needs to be considered.Based on the typical mechanical behavior of 7075-T651 aluminum alloy under high strain rate during the cutting process,this thesis studies the transformation of the plastic deformation control mechanism under different strain rates,analyzes the influence of the strain rate on the flow stress during the plastic deformation of the aluminum alloy,reveales the essence and generation mechanism of the 7075 aluminum alloy strain rate effect,and clarifies that the plastic deformation under high stress rate.The main research contents are as follows:1.Based on the source of Frank-Read dislocations,the evolution formulas of stress and strain rate are proposed.This formula describes the microscopic control mechanism of plastic deformation,and uses dislocation density as an internal variable.It is clear that the micro-control mechanism of plastic deformation will change from heat activation to dislocation damping mechanism with the increase of strain rate.And the critical strain rate is obtained when the flow stress of the material increases sharply with the sensitivity of the strain rate.2.Using dislocation density as an internal variable,coupling cutting speed,temperature,strain,strain rate,stress and other parameters,a viscous constitutive equation describing the cutting process was constructed,and the change rule of the above cutting parameters was obtained.The effect of strain rate on the plastic deformation process is studied from the microcosmic point of view.Based on the relationship between cutting speed and hardness,the theoretical model of strain rate and flow stress is established,which provides theoretical support for the verification of strain rate effect of aluminum alloy.3.Through orthogonal cutting experiments,the influence law of strain rate on chip morphology,chip ductile-brittle fracture transition and chip hardness was studied.Based on the interdependence of material strength and hardness,the strain rate effect of aluminum alloy was verified by measuring the Vickers hardness of the chip adiabatic shear band and the matrix.And the macroscopic viscous behavior of material plastic deformation under high strain rate was clarified4,The effect of strain rate on the control mechanism of plastic deformation is studied.The stress-strain curve of 7075-T651 aluminum alloy in a wide range of strain rate was studied by SHPB test.The change rule of strain rate sensitivity was analyzed,and the viscous behavior of plastic deformation under high strain rate was verified.5.The viscous behavior of plastic deformation in the cutting process is verified by the finite element analysis.Through the finite element analysis and calculation,the stress values of plastic deformation under different cutting speeds are obtained,and the strain rate effect of aluminum alloy is studied.