高氮奥氏体不锈钢高温动态响应特性及本构关系

在293~873 K的环境下,采用分离式霍普金森杆装置对高氮钢试样进行了102~103 s-1应变率下的动态加载实验。结合准静态实验结果,分析了应变率和温度对材料塑性流动特性的影响。结果表明:高氮钢的动态力学行为具有很强的应变率敏感性和温度敏感性。当应变率达到400 s-1或更高时,流动应力随应变率的增加显著升高;在同一应变率下,流动应力随温度的降低明显升高。研究了温度和应变率耦合效应对材料塑性行为的影响,得出温度软化效应在高氮钢高温动态塑性变形中起主导作用。基于经典的Johnson-Cook（J-C）模型,通过对实验数据的分析,得出了高氮钢材料的修正J-C本构方程,经验证修正J-C方程预测结果与实验结果吻合。     

宽应变率范围下2A16-T4铝合金动态力学性能

为了研究2A16-T4铝合金的动态力学性能,利用电子万能试验机、高速液压伺服试验机及霍普金森压杆(SHPB)装置进行常温下准静态、中应变率和高应变率的动态力学性能实验,得到不同应变率下的应力应变曲线,基于修正的Johnson-Cook本构模型对它进行拟合,并分析材料中应变率力学特性对模型应变率敏感参量的影响。结果表明:2A16-T4铝合金在应变率10-4~102 s-1范围内应变率敏感性较弱,而在102~103 s-1范围内应变率敏感性较强,且应变率强化效应随塑性应变的增大而减小;同时,在10-4~103 s-1范围内具有较强的应变硬化效应,且应变硬化效应随应变率的增大而减小;此外,修正Johnson-Cook本构模型的拟合结果与实验结果吻合很好,能够很好表征材料的动态力学行为,且考虑材料中应变率力学特性可提高本构模型参量的准确性。     

5A06铝合金的动态本构关系实验

运用材料试验机和分离式霍普金森压杆装置(SHPB)对3种不同加工及热处理状态的5A06铝合金在常温~500 C、应变率为10-4~103 s-1 下的力学行为进行了实验研究。基于Johnson-Cook (JC) 本构模型,通过实验数据拟合得到了每种状态下材料的本构模型参量。对Johnson-Cook本构模型中的应变率强化项作了修正,修正后的Johnson-Cook本构模型与实验数据基本吻合,从而确立了3种状态下5A06铝合金的动态本构关系。     

多晶纯钛在高应变率不同温度下的拉伸力学行为实验研究

利用MTS809和自行研制的旋转盘冲击拉伸试验机,对多晶纯钛进行了应变率为0.001s-1和300s-1、温度为298K至973K的拉伸试验和应变率为300 s-1不同温度下的冲击拉伸复元试验,得到了多晶纯钛的拉伸应力应变曲线和高应变率等温应力应变曲线。试验结果表明,多晶纯钛的拉伸力学行为具有应变率和温度相关性。采用修正的Johnson-Cook模型进行数值拟合,结果表明,该本构模型能较好地表征多晶纯钛在试验应变率和温度范围内的拉伸力学行为。     

Q235B钢动态本构及在LS-DYNA中的应用

采用万能材料试验机和分离式霍普金森拉杆（SHTB）装置,对我国钢结构建筑中最常用的Q235B钢进行准静态拉伸实验、高温拉伸实验和动态拉伸实验。基于实验数据对LS-DYNA常用的3种动态材料模型Cowper-Symonds本构模型、Johnson-Cook本构模型、Zerilli-Armstrong本构模型进行了拟合,通过Taylor杆实验对3种本构模型进行验证和对比分析。结果表明:Q235B钢具有较为明显的高温软化和应变率强化效应;Cowper-Symonds本构模型可以较好地适用于工程领域低速碰撞的模拟;Johnson-Cook本构模型可适用于较大应变率范围内的模拟;不推荐Zerilli-Armstrong本构模型在工程低速碰撞领域中使用。     

7A04铝合金的本构关系和失效模型

使用万能材料试验机、扭转试验机和Taylor撞击实验研究了高强铝合金7A04在常温至250 ℃的 准静态、动态本构关系和失效模型。基于实验结果,修改了Johnson-Cook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,并结合数值模拟标定了模型参数。实验结果表明,7A04铝合金的 应变和应变率强化效应不显著,失效应变随温度的增加、应力三轴度的减小和应变率的减小而增加。     

一种高强度钢的动态力学本构参数识别和数值模拟

分析了N-1钢在不同应变率条件下(10-3~103s-1)的应力应变关系实验结果,得到了N-1钢的应 变率强化特性。修正了平板试件断裂面中心的真实应力,并通过对真实应变与最小截面的厚度缩减率关系的 研究,得到了断裂面中心的真实应变,从而识别出了N-1钢的修正Johnson-Cook本构模型的参数。利用所确 定的本构关系模型,对N-1钢平板试件的杆-杆型冲击拉伸过程进行了数值模拟,模拟结果与实验结果较吻 合,验证了采用的修正的Johnson-Cook本构模型参数的实验识别方法以及数值模拟方法的正确性。     

45号钢的动态力学性能研究

对45号钢在不同环境温度(25 300℃)和不同应变率(10-4～103s-1)的 关系进行了研究。修正了Johnson Cook模型中的应变率强化系数C,确定了45号钢的本构关系。金相观察表明,与应变率强化相比,较高的环境温度使硬化速率降低,且占主要因素,其结果使材料的强度降低。透射电镜分析表明,高应变率在使位错运动的能量提高的同时,增加了位错在晶界处的阻力,而较高的环境温度则为位错提供了较多的滑移面和滑移方向,其结果是使材料更容易压缩。     

MDYB-3有机玻璃在不同应变率下的一维屈服行为

对MDYB-3有机玻璃进行了多组不同应变率(10-3~3 000 s-1)下的压缩实验, 得到准静态下的屈服应力与动态下的峰值应力。沿其增强与面内2个方向进行准静态压缩实验, 以分析定向拉伸对屈服应力的影响, 修正了Ree-Eyring模型与Cooperative模型以描述定向有机玻璃的屈服行为。采用Johnson-Cook模型描述屈服后的黏塑性行为。结果表明Cooperative屈服模型比Ree-Eyring屈服模型更接近实验结果, 且能准确描述准静态屈服应力。动态压缩下的峰值应力为失效应力, 说明试样在1 500 s-1以上应变率下未达到屈服应力时已经发生破坏。Johnson-Cook模型对于单条曲线拟合良好, 但无法准确描述材料的应变率相关性。     

金属材料两种常用本构模型的比较

介绍了两种常用的本构模型，即J－C模型和Z－A模型，就两种模型各自对应变率强化效应、温度软化效应和不同温度或应变率下应变强化行为的不同描述方式进行了比较与分析，讨论了两种模型的适用范围。     

Behaviors of three BCC metal over a wide range of strain rates and temperatures: experiments and modeling

The elastic–plastic behaviors of three body-centered cubic metals, tantalum, tantalum alloy with 2.5% tungsten, and AerMet 100 steel, are presented over a wide range of strains (15%), strain rates (10⁻⁶–10⁴ s⁻¹) and temperatures (77–600°F). Johnson-Cook and Zerilli-Armstrong models were found inadequate to describe the observations. A new viscoplastic model is proposed based on these experimental results. The proposed constitutive model gives good correlations with these experimental results and strain-rate jump experiments. In the next paper (Liang, R., Khan A.S., 2000. Behaviors of three BCC metals during non-proportional multi-axial loadings and predictions using a recently proposed model. International Journal of Plasticity, in press), multi-axial loading results on these materials and comparison with the proposed model will be presented.     

Influence of temperature and strain rate on the mechanical behavior of three amorphous polymers: Characterization and modeling of the compressive yield stress

Uniaxial compression stress–strain tests were carried out on three commercial amorphous polymers: polycarbonate (PC), polymethylmethacrylate (PMMA), and polyamideimide (PAI). The experiments were conducted under a wide range of temperatures (−40 °C to 180 °C) and strain rates (0.0001 s⁻¹ up to 5000 s⁻¹). A modified split-Hopkinson pressure bar was used for high strain rate tests. Temperature and strain rate greatly influence the mechanical response of the three polymers. In particular, the yield stress is found to increase with decreasing temperature and with increasing strain rate. The experimental data for the compressive yield stress were modeled for a wide range of strain rates and temperatures according to a new formulation of the cooperative model based on a strain rate/temperature superposition principle. The modeling results of the cooperative model provide evidence on the secondary transition by linking the yield behavior to the energy associated to the β mechanical loss peak. The effect of hydrostatic pressure is also addressed from a modeling perspective.     

PP/PA共混高聚物在高应变率下的热粘弹性本构关系和时温等效性

采用Instron1342电液伺服试验机和改进的SHPB技术对以113材料为例的PP/PA共混高聚物进行了应变率在10-4~103 s-1宽广范围,温度为25、40、60、80 ℃下的一维应力力学性能试验。结果表明,这类共混高聚物的力学响应对温度和应变率都是敏感的。以朱-王-唐非线性粘弹性本构方程来描述这类PP/PA共混高聚物的力学响应,并拟合得到了其热粘弹性本构参数,理论预言与试验结果在应变小于7%时吻合良好。对113材料20~80 ℃温度范围内不同应变率下的试验结果进行分析,证明PP/PA共混高聚物存在率温等效关系,提高温度和增加作用时间（减小应变率）的效果相当,反之,降低温度与减少作用时间（提高应变率）的效果相当。通过引入量纲一参量Z,使应变率d/dt、温度T这2个参量归结为统一的Z参量,从而得到了体现时温等效性的统一曲线。     

DH36钢拉伸塑性流动特性及本构关系

对DH36钢在温度从293~800 K、应变率为0.001和0.1 s-1的拉伸塑性流动特性进行实验研究,通过端口形貌图对变形前后的试样进行了微观分析,结果表明:(1)在实验温度范围内,0.001和0.1 s-1的应变率下,第三型应变时效现象出现,随应变率的增加,时效发生的温度区域移向更高温度;(2)第三型应变时效的发生与合金原子在晶界和晶粒中大量的第二相析出强化有关联;(3)建立包含第三型应变时效现象的统一本构模型,通过比较该模型能够较好的预测DH36的塑性拉伸流动应力。     

High-temperature pressure-shear plate impact experiments using pure tungsten carbide impactors

The pressure-shear plate impact experiment has been modified to test materials at high temperatures (up to 700°C). Together with the high strain rates characteristic of this experiment (10⁶ s^–1), the high-temperature capability allows the shearing resistance of materials to be measured under conditions unattainable with other testing equipment. The compressive and shear responses of pure tungsten carbide at different temperatures are presented, as well as the results of one test on OFHC copper at a temperature of 691°C and a shear strain rate of 1.4×10⁶ s^–1.     

A Phenomenological Constitutive Model for Describing Thermo-Viscoplastic Behavior of Al-Zn-Mg-Cu Alloy Under Hot Working Condition

In order to predict the high-temperature deformation behavior of Al-Zn-Mg-Cu alloy, the hot compression tests were conducted in the strain rate range of (0.001–0.1)s⁻¹ and the forming temperature range of (573–723) K. Based on the experimental results, Johnson-Cook model was found inadequate to describe the high-temperature deformation behavior of Al-Zn-Mg-Cu alloy. Therefore, a new phenomenological constitutive model is proposed, considering the coupled effects of strain, strain rate and forming temperature on the material flow behavior of Al-Zn-Mg-Cu alloy. In the proposed model, the material constants are presented as functions of strain rate. The proposed constitutive model correlates well with the experimental results confirming that the proposed model can give an accurate and precise estimate of flow stress for the Al-Zn-Mg-Cu alloy investigated in this study.     

Thermomechanical behavior of casting sands: Experiments and elastoplastic modeling

The thermomechanical behavior of casting sands is discussed from an experimental and a theoretical point of view. Uniaxial compression tests at temperatures ranging from 20°C to 950°C and at different values of strain rate (ϵ = 10⁻² s⁻¹, ϵ = 10⁻³ s⁻¹ and ϵ = 10⁻⁴ s⁻¹) have been performed. They show that casting sands exhibit no strain rate effect in the temperature range 20–600°C, and that an elastoplastic model is well suited to describe the experimental results. Three thermoelastoplastic models, derived from Cam Clay and Hujeux models have been developed. These new models take into account the cohesion of the material. The physical parameters needed for these models have been obtained in the temperature range 20–300°C by using triaxial tests, uniaxial compression tests, isotropic compression tests and die pressing tests. An original triaxial apparatus has been built allowing a temperature of 800°C and a pressure of 4 MPa to be reached. In the temperature at which the parameters have been obtained (20–300°C), two additional triaxial compression tests at different confining pressures are used to check the validity of the thermoelastoplastic models used. The best quantitative results are obtained with the revised modified Cam Clay model.