A modified Johnson–Cook model for 7N01 aluminum alloy under dynamic condition

Tensile tests at different strain rates(0.0002, 0.002, 0.02, 1000 and 3000 s^(-1)) were carried out for 7N01 aluminum alloy. Low strain rate experiments(0.0002, 0.002 and 0.02 s^(-1)) were conducted using an electronic mechanical universal testing machine, while high strain rate experiments(1000, 3000 s^(-1)) were carried out through a split Hopkinson tensile bar. The experimental results showed that 7N01 aluminum alloy is strain rate sensitive. By introducing a correction scheme of the strain rate hardening coefficient, a modified Johnson–Cook model was proposed to describe the flow behaviors of 7N01 aluminum alloy. The proposed model fitted the experimental data better than the original Johnson–Cook model in plastic flow under dynamic condition. Numerical simulations of the dynamic tensile tests were performed using ABAQUS with the modified Johnson–Cook model. Digital image correlation was used together with high-speed photography to study the mechanical characters of specimen at high strain rate. Good correlations between the experiments results, numerical predictions and DIC results are achieved. High accuracy of the modified Johnson-Cook model was validated.

The modified temperature term on Johnson-Cook constitutive model of AZ31 magnesium alloy with {0002} texture

The dynamic compression experiments with Split-Hopkinson Pressure Bar(SHPB)were performed on AZ31 magnesium alloy rolled sheet specimens in the normal direction(AZ31-ND)with{0002}texture at the temperature of 293-523 K and the strain rate of 0.001-2200 s^−1.The temperature term in Johnson-Cook(JC)constitutive model had been reasonably modified.This advantage made constitutive model promising for decribing the dynamic deformation behavior of AZ31-ND with{0002}texture more accurately.The obtained true stress-true plastic strain curves agreed well with the measured results in a wide range of strain rates and temperatures.The thermal softeninging,strain and strain rate hardening effect on the AZ31-ND with{0002}texture were discussed.The adiabatic shear band(ASB)of AZ31-ND with{0002}texture hat shaped specimen was successfully predicted by combining modified JC constitutive model and numerical simulation,which was also validated by Electron Back-Scattered Diffraction(EBSD)map under the same boundary condition.

基于全局响应面算法的Q235B钢的Johnson-Cook模型参数最优

This study investigates the mechanical properties of Q235B steel through quasi-static tests at both room temperature and elevated temperature.The initial values of the Johnson-Cook model parameters are determined using a fitting method.The global response surface algorithm is employed to optimize and calibrate the Johnson-Cook model parameters for Q235B steel under both room temperature and elevated temperature conditions.A simulation model is established at room temperature,and the simulated mechanical performance curves for displacement and stress are monitored.Multiple optimization algorithms are applied to optimize and calibrate the model parameters at room temperature.The global response surface algorithm is identified as the most suitable algorithm for this optimization problem.Sensitivity analysis is conducted to explore the impact of model parameters on the objective function.The analysis indicates that the optimized material model better fits the experimental values,aligning more closely with the actual test results of material strain mechanisms over a wide temperature range.

基于Johnson-Cook模型的剪切闸板性能仿真

目前有关剪切闸板性能分析多集中于闸板应力分析及钻杆参数分析,而对连续管规格、剪切闸板刃口夹角对剪切力的影响研究还不够系统和深入。为此,以Johnson-Cook模型为基础,建立了剪切闸板剪切连续管有限元模型,对剪切连续管过程中的剪切应力进行了分析,同时分析了连续管壁厚、长度及剪切闸板V形夹角等参数对剪切应力的影响。研究结果表明:随着连续管壁厚的不断增加,剪切力峰值总体呈上升趋势,在塑性变形阶段之前剪切力平缓上升,塑性变形之后上升幅度较大;随着连续管长度的不断增加,其剪切应力在不断减小,3000 m以上连续管,剪切应力明显下降,主要原因是下端拉力在剪切作业中起到了主导作用;随着剪切闸板V形夹角的增加,剪切应力先减少后增加,V形夹角在158°时,上、下闸板应力最优。所得结论可为连续管剪切闸板的结构设计及连续管剪切性能分析提供参考。

高强2A12铝合金修正Johnson-Cook本构模型

为了研究2A12铝合金在不同应变率和不同温度下的塑性流动应力特征及其本构模型,首先对该铝合金开展了不同应变率(10^(-4)~10^(-1)s^(-1))和不同温度(300~400 K)下的准静态拉伸实验研究。然后,利用实验数据对经典Johnson-Cook(J-C)模型参数进行标定,并对模型加以验证。最后,基于经典J-C模型预测准确性不高的现象,建立了修正J-C本构模型,并利用450 K下的实验数据进行了模型验证。结果表明:2A12铝合金的应变率强化效应不显著,而温度软化效应较为显著。随着温度升高,准静态屈服强度显著下降,300 K下准静态屈服强度可达432 MPa,而400 K下准静态屈服强度为270 MPa。修正J-C本构模型预测与实验数据吻合更好,表明本文建立的修正J-C本构模型及参数能够更好地描述2A12铝合金在不同应变率和不同温度下的塑性流动应力特性。

基于Arrhenius模型和修正Johnson-Cook模型的TC21钛合金流动应力预测

使用Gleeble-3500热模拟试验机对TC21钛合金在温度为890~990℃、应变速率为0.01~10 s~(-1)下进行了热模拟压缩实验,研究了该合金的高温流变行为。在变形条件下,该合金的流变应力随应变的增大逐渐增加,在达到峰值后又逐渐减小。基于实验数据,分别采用Arrhenius模型和修正Johnson-Cook模型构建了TC21钛合金本构模型,并对这两个模型的预测精度进行了分析对比。结果表明,修正Johnson-Cook本构模型预测值的平均绝对相对误差e_(AARE)为7.2078%,相关系数r为0.96866;Arrhenius本构模型预测值的e_(AARE)为12.6699%,r为0.95794,修正Johnson-Cook本构模型的精度高于Arrhenius本构模型,且在整个参数范围内具有一定的精度,可以较好地描述TC21钛合金的高温流变行为。

B280VK高强钢的Johnson-Cook本构模型与失效参数确定

通过对B280VK高强钢进行动态和准静态拉伸试验获取了其相关力学性能,并基于Johnson-Cook本构模型反求出B280VK高强钢的本构模型参数。结果表明,Johnson-Cook本构模型拟合曲线与试验拉伸曲线具有较高的一致性,能够反映出B280VK高强钢材料拉伸应力及应变变化趋势,可用于预测B280VK高强钢的应力-应变关系。然后,利用不同缺口样件准静态和动态拉伸载荷工况下获得的失效应变和应力三轴度值,通过最小二乘法拟合获得Johnson-Cook失效模型参数。最后,通过对比仿真与试验结果发现仿真与试验的载荷-位移曲线具有较高的一致性,并且峰值载荷最大相对误差被控制在9.23%以内,验证了B280VK高强钢的Johnson-Cook失效模型的准确性。

超声振动辅助SUS304薄带塑性变形的Johnson-Cook本构模型

通过超声能场辅助SUS304薄带拉伸试验发现,薄带塑性变形过程中的流动应力明显下降,体现了超声的软化效应。硬化指数和硬化系数随着超声能量的增加呈指数增加,且伸长率也发生了明显的下降,说明超声能场的加入对材料产生了硬化作用。相较于常规拉伸,施加超声能场后薄带的应变速率也发生了明显的提升,说明超声提高了薄带的应变速率敏感性。基于Johnson-Cook本构模型,建立了超声能场作用下SUS304薄带塑性变形的本构模型,用于定量分析超声能场振幅对SUS304薄带塑性变形的影响。

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.

基于修正Johnson-Cook本构模型的奥氏体不锈钢高温流变行为

文章研究了修正的Johnson-Cook(m-JC)本构模型对304奥氏体不锈钢高温流变行为的表征能力。利用不同温度、应变和应变速率等温热压缩试验的试验真应力-应变数据来计算本构模型的材料常数,建立了关于304奥氏体不锈钢的m-JC本构模型。通过比较预测结果的相关系数、平均相对误差以及均方差,评估了模型的适用性。结果表明,修正的JC模型预测结果和试验结果之间的平均相对误差绝对值为6.77%,相关系数为0.987,均方差为11.2 MPa,m-JC本构模型可以较为准确的描述304奥氏体不锈钢的流变行为。

Temperature distribution in adiabatic shear band for ductile metal based on JOHNSON-COOK and gradient plasticity models

Gradient-dependent plasticity considering interactions and interplay among microstructures was included into JOHNSON-COOK model to calculate the temperature distribution in adiabatic shear band(ASB), the peak and average temperatures as well as their evolutions. The differential local plastic shear strain was derived to calculate the differential local plastic work and the temperature rise due to the microstructural effect. The total temperature in ASB is the sum of initial temperature, temperature rise at strain-hardening stage and non-uniform temperature due to the microstructural effect beyond the peak shear stress. The flow shear stress—average plastic shear strain curve, the temperature distribution, the peak and average temperatures in ASB are computed for Ti-6Al-4V. When the imposed shear strain is less than 2 and the shear strain rate is 1 000 s?1, the dynamic recovery and recrystalliza-tion processes occur. However, without the microstructural effect, the processes might have not occurred since heat diffusion decreases the temperature in ASB. The calculated maximum temperature approaches 1 500 K so that phase transformation might take place. The present predictions support the previously experimental results showing that the transformed and deformed ASBs are observed in Ti-6Al-4V. Higher shear strain rate enhances the possibility of dynamic recrystallization and phase transformation.

Adiabatic shear localization evolution for steel based on the Johnson-Cook model and gradient-dependent plasticity

Gradient-dependent plasticity is introduced into the phenomenological Johnson-Cook model to study the effects of strainhardening, strain rate sensitivity, thermal-softening, and microstructure. The microstructural effect （interactions and interplay among microstructures） due to heterogeneity of texture plays an important role in the process of development or evolution of an adiabatic shear band with a certain thickness depending on the grain diameter. The distributed plastic shear strain and deformation in the shear band are derived and depend on the critical plastic shear strain corresponding to the peak flow shear stress, the coordinate or position, the internal length parameter, and the average plastic shear strain or the flow shear stress. The critical plastic shear strain, the distributed plastic shear strain, and deformation in the shear band are numerically predicted for a kind of steel deformed at a constant shear strain rate. Beyond the peak shear stress, the local plastic shear strain in the shear band is highly nonuniform and the local plastic shear deformation in the band is highly nonlinear. Shear localization is more apparent with the increase of the average plastic shear strain. The calculated distributions of the local plastic shear strain and deformation agree with the previous numerical and experimental results.

15CrMoG耐高温合金钢Johnson-Cook本构模型建立与精度分析

目的掌握不同条件下15CrMoG的高温流变规律。方法在变形温度为1173.15、1273.15、1373.15、1473.15K,应变速率为5、10、15、20s^(-1)条件下,对15CrMoG进行等温压缩实验。根据实验数据构建15CrMoG的Johnson-Cook本构模型,并对应变速率强化参数C和温度敏感系数D进行分别修正和同时修正。将修正后的3种模型预测值与实验值进行线性拟合,分别得到各模型的相关系数。引入相对误差ARE函数,计算不同条件下各模型的平均误差,通过对比得到精度较高的模型。结果15CrMoG具有温度和应变速率敏感性,高温流变曲线整体呈现先上升后平稳的趋势。拟合取值的局限性导致未修正的本构模型的精度较差。在较低变形温度下,修正后的模型均具有良好的预测精度,在高变形温度下,修正温度敏感系数的模型具有更好的适应性。3种修正模型预测值与实验值的线性相关系数均在0.9以上,具有良好的相关性。在低变形温度下,3种模型的相对误差均较小;在高变形温度下,修正温度敏感系数的Johnson-Cook模型具有较高的预测精度,最大误差为4.75%。结论对Johnson-Cook进行修正可更准确地描述15CrMoG的高温变形行为,其中修正温度敏感系数模型的误差最小,为推荐本构模型。

Adiabatic Shear Localization for Steels Based on Johnson-Cook Model and Second-and Fourth-Order Gradient Plasticity Models

To consider the effects of the interactions and interplay among microstructures, gradient-dependent models of second- and fourth-order are included in the widely used phenomenological Johnson-Cook model where the effects of strain-hardening, strain rate sensitivity, and thermal-softening are successfully described. The various parameters for 1006 steel, 4340 steel and S-7 tool steel are assigned. The distributions and evolutions of the local plastic shear strain and deformation in adiabatic shear band （ASB） are predicted. The calculated results of the second- and fourth- order gradient plasticity models are compared. S-7 tool steel possesses the steepest profile of local plastic shear strain in ASB, whereas 1006 steel has the least profile. The peak local plastic shear strain in ASB for S-7 tool steel is slightly higher than that for 4340 steel and is higher than that for 1006 steel. The extent of the nonlinear distribution of the local plastic shear deformation in ASB is more apparent for the S-7 tool steel, whereas it is the least apparent for 1006 steel. In fourth-order gradient plasticity model, the profile of the local plastic shear strain in the middle of ASB has a pronounced plateau whose width decreases with increasing average plastic shear strain, leading to a shrink of the portion of linear distribution of the profile of the local plastic shear deformation. When compared with the sec- ond-order gradient plasticity model, the fourth-order gradient plasticity model shows a lower peak local plastic shear strain in ASB and a higher magnitude of plastic shear deformation at the top or base of ASB, which is due to wider ASB. The present numerical results of the second- and fourth-order gradient plasticity models are consistent with the previous numerical and experimental results at least qualitatively.

Q235B钢Johnson-Cook模型参数的确定

使用万能材料试验机、扭转试验机和霍普金森拉杆装置研究了Q235B钢在常温~950℃的准静态、动态力学性能,获得了Q235B强度与等效塑性应变,应变率和温度的关系以及延性与应力三轴度,应变率和温度的关系。基于实验结果,修改了Johnson-Cook（J-C）强度模型中的应变强化项以及Johnson-Cook失效模型中的温度软化项,并结合数值仿真标定了相关模型参数。最后通过Taylor撞击试验验证了模型参数的有效性。

一种调质50SiMnVB钢Johnson-Cook本构模型的建立

研究正火、正火+淬火+中/低温回火、调质处理的50SiMnVB钢的硬度及微观组织,发现50SiMnVB钢通过860℃×120 min(油冷)淬火+600℃×60 min(水冷)回火这种调质工艺处理后,具有较好的综合力学性能。利用电子万能材料试验机和SHPB实验装置对这种调质工艺处理后的50SiMnVB钢常温下的准静态和动态力学特性进行了测试,得出材料在不同应变率下的应力-应变曲线;采用参数识别法和最小二乘法建立了调制50SiMnVB钢较宽应变率下的Johnson-Cook本构模型,和实验结果吻合较好。

基于Johnson-Cook黏塑性模型的沥青路面车辙计算

采用Johnson-Cook模型描述沥青混合料黏塑性本构关系,通过不同温度和不同应变率下单轴压缩试验确定沥青和改性沥青混合料的Johnson-Cook黏塑性模型参数,利用ANSYS瞬态动力学分析理论,分析了在设计年限内当量轴次和超载等不同条件下对沥青路面车辙变形的影响。结果表明:使用天然岩沥青改性沥青面层比基质沥青面层的抗车辙性能均提高20%,符合沥青路面车辙变形实际情况;基于Johnson-Cook黏塑性模型的车辙计算方法,为沥青路面车辙研究提供了一种新的思路和技术途径。

大口径薄壁Ti-6Al-4V管材数控温弯中不同应变速率和温度下的Johnson-Cook本构模型（英文）

大口径薄壁Ti-6Al-4V管是航空航天等高端制造领域亟需的典型轻量化高性能构件,数控温弯能够有效实现大口径Ti-6Al-4V管的精确成形。由于数控温弯工艺过程是多场耦合复杂变形过程,建立其材料本构模型并实现全过程有限元模拟是亟待解决的瓶颈技术。利用管材单向拉伸实验,结合温弯工艺参数变化,研究温度在25~600°C和应变速率在0.00067~0.1 s^(-1)情况下Ti-6Al-4V管的力学性能。考虑非线性硬化率和应变的交互作用,建立了修正的Johnson-Cook本构模型,并根据实验数据对相关修正参数进行了拟合。将该模型应用于温弯模拟中可发现,修正的JC模型与传统的模型相比,可降低最大误差90%,并且可以有效预测管材断裂、起皱等成形缺陷发生的位置,为大口径薄壁Ti-6Al-4V管数控温弯成形极限和工艺优化奠定基础。

国产C30混凝土考虑率型微损伤演化的改进Johnson-Cook强度模型

采用Instron1342液压伺服试验机和改进的SHPB技术对国产C30混凝土进行了应变率在一定宽广范围的一维应力下力学性能试验,采用Johnson-Cook强度模型的框架,确定适用于大变形、高应变率及高压下混凝土数值计算的等效强度模型的率相关参数及其他材料常数。由对C30混凝土的大量试验表明,混凝土损伤演化是同时依赖于应变与应变率的率相关过程,提出适用于工程应用的率型损伤演化律来描述C30混凝土的损伤演化过程,并确定了损伤演化常数。由于材料参数小于1,对应于材料的冲击韧化的过程,与国产C30混凝土动态试验结果相吻合。