Effects of constitutive parameters on adiabatic shear localization for ductile metal based on JOHNSON-COOK and gradient plasticity models

By using the widely used JOHNSON-COOK model and the gradient-dependent plasticity to consider microstructural effect beyond the occurrence of shear strain localization,the distributions of local plastic shear strain and deformation in adiabatic shear band(ASB)were analyzed.The peak local plastic shear strain is proportional to the average plastic shear strain,while it is inversely proportional to the critical plastic shear strain corresponding to the peak flow shear stress.The relative plastic shear deformation between the top and base of ASB depends on the thickness of ASB and the average plastic shear strain.A parametric study was carried out to study the influence of constitutive parameters on shear strain localization.Higher values of static shear strength and work to heat conversion factor lead to lower critical plastic shear strain so that the shear localization is more apparent at the same average plastic shear strain.Higher values of strain-hardening exponent,strain rate sensitive coefficient,melting point,thermal capacity and mass density result in higher critical plastic shear strain,leading to less apparent shear localization at the same average plastic shear strain.The strain rate sensitive coefficient has a minor influence on the critical plastic shear strain,the distributions of local plastic shear strain and deformation in ASB.The effect of strain-hardening modulus on the critical plastic shear strain is not monotonous.When the maximum critical plastic shear strain is reached,the least apparent shear localization occurs.

Identification of constitutive model parameters for nickel aluminum bronze in machining

The material of nickel aluminum bronze (NAB) presents superior properties such as high strength, excellent wear resistance and stress corrosion resistance and is extensively used for marine propellers. In order to establish the constitutive relation of NAB under high strain rate condition, a new methodology was proposed to accurately identify the constitutive parameters of Johnson?Cook model in machining, combining SHPB tests, predictive cutting force model and orthogonal cutting experiment. Firstly, SHPB tests were carried out to obtain the true stress?strain curves at various temperatures and strain rates. Then, an objective function of the predictive and experimental flow stresses was set up, which put the identified parameters of SHPB tests as the initial value, and utilized the PSO algorithm to identify the constitutive parameters of NAB in machining. Finally, the identified parameters were verified to be sufficiently accurate by comparing the values of cutting forces calculated from the predictive model and FEM simulation.

Flow stress behavior and constitutive modeling of 20MnNiMo low carbon alloy

The hot deformation behavior of 20 Mn Ni Mo low carbon alloy was investigated by isothermal compression tests over wide ranges of temperature(1223-1523 K) and strain rate(0.01-10 s^(-1)). According to the experimental true stress-true strain data, the constitutive relationships were comparatively studied based on the Arrhenius-type model, Johnson-Cook(JC) model and artificial neural network(ANN), respectively. Furthermore, the predictability of the developed models was evaluated by calculating the correlation coefficient(R) and mean absolute relative error(AARE). The results indicate that the flow stress behavior of 20 Mn NiM o low carbon alloy is significantly influenced by the strain rate and deformation temperature. Compared with the Arrhenius-type model and Johnson-Cook(JC) model, the ANN model is more efficient and has much higher accuracy in describing the flow stress behavior during hot compressing deformation for 20 Mn Ni Mo low carbon alloy.

Dynamic Constitutive Model of Physical Simulation in High-Speed Blanking for C5191 Phosphor Bronze

Strain hardening,strain rate strengthening and thermal softening data of C5191 phosphor bronze at highspeed blanking are not easy to be obtained with a general measure method,therefore,it is quite difficult to establish the dynamic constitutive model.To solve this problem,the tensile properties at a strain rate of 1 s^(-1) by GLEEBLE-3500,and dynamic tensile conditions at strain rates of 500,1 000 and 1 500 s^(-1) by split Hopkinson tensile bar (SHTB) apparatus are studied.According to these test data,the classic Johnson-Cook equation is modified.Furthermore,the modified Johnson-Cook equation is validated in the physical simulation model of high-speed blanking.The results show that the strength of C5191 phosphor bronze maintains a certain degree of increase as the strain rate increasing and presents a clear sensitivity to strain rate.The modified Johnson-Cook equation,which has better description accuracy than the classical Johnson-Cook equation,can provide important material parameters for physical simulation models of its high-speed blanking process.

Constitutive Models for Compressive Deformation of AZ80Magnesium Alloy under Multiple Loading Directions and Strain Rates

Two constitutive models,the modified Johnson-Cook model and the logarithm linear relation model based on empirical approach and data analysis,were presented to illustrate compressive deformation of magnesium alloys AZ80 under multiple loading directions and strain rates.The results of stress-strain curve analysis and sensitivity index analysis suggested that the stress held large fluctuations in loading direction of 90°.Model testing signified that the logarithm linear relation model was more proper than the modified Johnson-Cook model in view of relative mean square error and correlation coefficients.Moreover,numerical simulation building on established models also indicated that the logarithm linear model is more precise than the modified Johnson-Cook model.

微细侧铣过程的有限元建模与仿真（英文）

建立了AISI 4340微细侧铣的二维有限元模型。将Johnson-Cook本构模型与JohnsonCook剪切失效模型相结合,对铣削刃旋转过程中的一个完整侧铣周期进行了仿真。由于没有考虑尺寸效应的影响,所得到的流动应力值偏小。因此,建立了应变梯度塑性模型,并应用其预测了切屑的形成、冯米斯应力和温度场。仿真结果显示:微细侧铣过程中存在尺度效应,与Johnson-Cook本构模型相比,应变梯度塑性模型能够很好地描述微细侧铣过程中的尺寸效应。最后,将仿真结果与理论计算结果相比较,验证了所建模型的正确性。

Influence of notch volume on mechanical properties of a novel high-strength and high-toughness steel

The effect of notch volume on the mechanical behavior of a novel high-strength and high-toughness steel with negative Poisson’s ratio effect(called NPR steel)was studied.First,the quasi-static tensile test of NPR steel with different notch volumes was carried out,and its failure characteristics and mechanical properties parameters were studied.Then,the modified Johnson-Cook(J-C)constitutive model with coupled notch volume ratio was proposed.The model was validated based on three-dimensional finite element numerical simulations.The results show that the engineering stress–strain curve of NPR steel has no yield platform,and has the mechanical properties of high strength,high elongation,and high energy absorption.Notch volume significantly affects the mechanical properties of NPR steel.The elongation,yield strength,tensile strength,and energy absorption characteristics of steel bar gradually decrease with the increase in notch volume.The notch volume ratio V^{*},a characteristic parameter describing the notch volume of reinforcement,is defined,and the quantitative relationship between this parameter and mechanical parameters is established,which can accurately characterize the mechanical properties of specimens with different notch volume ratios.Based on the true stress–strain curves with different notch volume ratios,a constitutive model with modified Johnson-Cook model parameters is proposed.The finite element results show that the modified J-C model can accurately fit the quasi-static tensile mechanical behavior of NPR steel.