循环稳定材料的棘轮行为：Ⅰ．实验和本构模型

在实验分析结果的基础上，对循环稳定材料的室温单轴和非比例多轴循环棘轮行为进行了本构描述，建立了一个简单而合理的、便于工程应用的粘塑性循环棘轮本构模型。给出了模型参数的确定方法，并根据实验获得的单拉应力．非弹性应变关系曲线确定了针对U71Mn轨道钢材料的参数值。在此基础上，通过对该材料棘轮行为的本构模拟检验了发展模型的预言能力。结果表明，模型具有很好的预测效果，模拟结果与对应的实验结果符合得很好。     

高强轨道钢双轴压-扭棘轮行为的实验和模拟

在室温下对高强轨道钢进行了单轴和非比例双轴压-扭循环变形行为的实验,讨论了不同加载路径对轨道钢棘轮变形行为的影响。结果显示：该轨道钢呈现出明显的循环软化效应和压缩方向的棘轮行为,且棘轮行为的演化表现出强烈的加载路径相关性;在椭圆路径下,棘轮应变较其他四种路径更小。进而建立了基于Abdel Karim-Ohno非线性随动硬化律的非比例多轴循环棘轮本构模型,并通过在随动硬化和各向同性软化律中引入非比例因子来考虑非比例路径对双轴压-扭棘轮行为的影响。实验结果和模拟结果的对比表明：该本构模型能够较好地模拟高强度轨道钢的非比例双轴压-扭棘轮行为。     

SiCP/6061Al合金复合材料高温时相关棘轮行为的数值模拟

基于颗粒增强金属基复合材料的单球形颗粒模型和轴对称二维6节点三角形单元, 利用ABAQUS对T6热处理后的两种体积分数的SiC_P/6061Al合金复合材料的高温(300℃)单轴拉伸行为和单轴棘轮行为进行数值模拟。在有限元模拟中, 对基体采用了新发展的、 能够合理描述材料棘轮行为的黏塑性循环本构模型。数值模拟表明: 本文中建立的有限元分析模型对颗粒增强金属基复合材料的高温单轴棘轮行为及其时间相关特性得到了较为合理的描述, 模拟结果与实验吻合较好。模拟结果同时还揭示了复合材料内循环变形行为在细观层次上的不均匀性和复杂性。      

一种预测复合材料棘轮行为的循环塑性-损伤模型

构建循环塑性本构模型并揭示其微观机制,目前仍然是复合材料力学研究富有挑战性的课题。本文提出了一种循环塑性-损伤模型,用以预测在循环载荷作用下纤维增强复合材料的应力-应变响应。该模型是在作者前期提出的描述非线性滞后行为的弹塑性本构模型的基础上的进一步扩展。它可以预测加载时的非线性响应、卸载和重加载时的迟滞行为及大量循环下的棘轮现象。作为基准问题验证,将Kawai等的实验数据与本文模型的数值预测进行了比较。结果表明,该模型能够模拟碳纤维/环氧树脂单向复合材料在偏轴循环加载下的棘轮行为。      

中碳贝氏体钢的室温单轴循环变形行为研究

为了了解中碳贝氏体钢支承辊的接触疲劳失效机制,对中碳贝氏体钢材料在室温单轴循环加载下的应变循环特性和棘轮行为进行了实验研究。讨论了材料的循环软/硬化特性及其对单轴棘轮行为的影响,同时揭示了该材料棘轮行为的平均应力、应力幅值及其加载历史的依赖性。实验研究表明:材料的循环软/硬化特性具有明显的应变幅值依赖性,进而导致材料在不同的应力水平下出现不同的棘轮行为。研究得到了一些有助于该类材料循环变形行为本构描述的结论。     

循环软化材料单轴时相关循环变形行为的实验研究

在室温下,对循环软化材料(调质42CrMo钢)的单轴时相关应变循环特性和时相关棘轮行为进行了实验研究。揭示了材料在不同加载速率、不同峰/谷值保持时间以及不同加载波形(三角波和正弦波)下的循环软化特性和棘轮行为特性。结果表明,在室温下,材料的循环软化和棘轮变形行为均体现出明显的时相关效应:其循环变形行为不仅依赖于加载速率,而且还明显依赖于保持时间以及加载波形的形状。研究有助于后续建立循环软化材料时相关循环本构模型。     

1Cr18Ni9不锈钢高温单轴时相关棘轮行为研究

在室温、250℃、500℃和650℃四种温度下对1Cr18Ni9不锈钢材料的单轴应变循环特性及其时相关棘轮行为进行了实验研究,以讨论不同加载速率、加载波形和峰值应力保持时间对材料棘轮行为的影响。实验结果表明:在室温下,材料呈现出弱的循环软化特性和渐进型棘轮变形行为,并对加载速率和峰值应力保持时间具有强烈依赖性;在250℃、650℃下,因材料的循环硬化加快而使其棘轮行为较快趋于安定,但棘轮变形大小仍一定程度依赖于加载速率和保持时间;在500℃温度下则由于动态应变时效的影响没有明显的棘轮行为发生。研究得到一些有助于后续建立时相关本构模型的结论。     

循环稳定材料的棘轮行为:Ⅱ.隐式应力积分算法和有限元实现

针对第一部分发展的、能够合理描述循环稳定材料棘轮行为的粘塑性本构模型,详细讨论该模型的数值计算方法和有限元实现。在径向回退(Radial Retulm)和向后欧拉积分方法的基础上,结合连续迭代(Successive Substimtionl方法,推导并建立了针对循环粘塑性本构模型的、新的隐式应力积分算法。为了本构模型在大型有限元分析程序(如ABAQUS等)中的实现,针对有限元的整体节点迭代计算,推导和确立了一个新的、考虑率相关塑性的一致切线刚度矩阵(Consistent Tangent Modulus)表达式。通过对一些算例的有限元分析,讨论了建立的隐式应力积分算法的优越性,同时对特定构件的棘轮行为进行了数值模拟,进而检验了有限元实现的合理性和必要性。     

循环稳定材料的棘轮行为:II.隐式应力积分算法和有限元实现

针对第一部分发展的、能够合理描述循环稳定材料棘轮行为的粘塑性本构模型,详细讨论该模型的数值计算方法和有限元实现.在径向回退(Radial Return)和向后欧拉积分方法的基础上,结合连续迭代(Successive Substitution)方法,推导并建立了针对循环粘塑性本构模型的、新的隐式应力积分算法.为了本构模型在大型有限元分析程序(如ABAQUS等)中的实现,针对有限元的整体节点迭代计算,推导和确立了一个新的、考虑率相关塑性的一致切线刚度矩阵(Consistent Tangent Modulus)表达式.通过对一些算例的有限元分析,讨论了建立的隐式应力积分算法的优越性,同时对特定构件的棘轮行为进行了数值模拟,进而检验了有限元实现的合理性和必要性.     

玻璃短纤维增强树脂基复合材料的单轴时间相关棘轮行为实验研究

对玻璃短纤维增强树脂基复合材料(短纤维体积分数：28%,40%)的室温单轴循环棘轮行为进行了实验研究,讨论了复合材料在不同加载条件下的棘轮变形特征。结果表明：该复合材料在宏观层次上表现出与基体相类似的棘轮变形规律,即在非对称应力循环下也将产生明显的棘轮变形,并随应力幅值和平均应力的增加而增加;树脂基复合材料的棘轮行为具有明显的时间相关特性,棘轮应变值依赖于应力率和峰值保持时间。在建立玻璃短纤维增强不饱和聚酯树脂基复合材料棘轮行为的本构模型时必须考虑基体的黏性变形特征。     

Uniaxial and non-proportionally multiaxial ratcheting of U71Mn rail steel: experiments and simulations

The ratcheting and strain cyclic characteristics of U71Mn rail steel were experimentally researched under uniaxial and non-proportionally multiaxial cyclic loading at room temperature. The effects of cyclic strain, stress and their histories on strain cyclic characteristics and ratcheting were studied, respectively. It is shown that: U71Mn rail steel exhibits a cyclic stabilization and non-memorization for previous loading history under strain cycling; however, the ratcheting of the material depends greatly not only on the current values of mean stress and stress amplitude, but also on their histories; the non-proportionality of multiaxial loading path only causes a negligible additional hardening for the material. Based on the Ohno–Wang non-linear kinematic hardening model [Int. J. Plast. 9 (1993) 375, 391], the uniaxial and multiaxial ratcheting behaviours of the material were simulated by a visco-plastic constitutive model. The simulated results are in good consistence with the experimental ones.     

Experimental Study on the Uniaxial Cyclic Deformation of 25CDV4.11 Steel

The strain cyclic characteristics and ratcheting behavior of 25CDV4.11 steel were studied by the experiments under uniaxial cyclic loading with relatively high cyclic number and at room temperature. The cyclic hardening/softening feature of the material was first observed under the uniaxial strain cycling with various strain amplitudes. Then, the ratcheting behavior of the material was researched in detail, and the effects of stress amplitude and mean stress on the ratcheting were discussed under uniaxial asymmetrical stress cycling. Comparing with the experimental results of SS316L stainless steel, it is concluded that the material exhibits remarkable cyclic softening feature, and then a special ratcheting behavior is caused. Some conclusions useful to establish corresponding constitutive model are obtained.     

Experimental Study on Non—proportional Multiaxial Strain Cyclic Characteristics and Ratcheting of U71Mn Rail Steel

An experimental study was carried out on the strain cyclic characteristics and ratcheting of U71Mn rail steel subjected to non-proportional multiaxial cyclic loading.The strain cyclic characteristics were researached under the strain-controlled circular load path.The ratcheting was investigated for the stress-controlled multiaxial circular,elliptical and rhombic load paths with different mean stresses,stress amplitudes and their histories.The experiment shows that U71Mn rail steel features the cyclic non-hardening/softening, and its strain cyclic characteristics depend greatly on the strain amplitude but slightly on its history.However,the ratcheting of U71Mn rail steel depends greatly not only on the values of mean stress and stress amplitude,but also on their histories.In the meantime,the shape of load path and its history also apparently influence the ratcheting.The ratcheting changes with the different loading paths.     

Uniaxial ratchetting in steels with different cyclic softening/hardening behaviours

The cyclic deformation of three structural steels, SS316L stainless steel, 40Cr3MoV bainitic steel and 25CDV4.11 steel, were studied experimentally by uniaxial cyclic straining or stressing tests at room temperature. The cyclic softening/hardening behaviours of the steels were discussed first by cyclic straining tests; and then the effects of cyclic softening/hardening behaviours on the uniaxial ratchetting of the materials were investigated by asymmetrical cyclic stressing tests. It is concluded from the experimental results that the ratchetting greatly depends on the cyclic softening/hardening behaviours of the materials, as well as the loading history. Different ratchetting and failure behaviours are observed for the prescribed steels. It is also stated that the proposed unified visco‐plastic constitutive model can provide a fairly reasonable simulation of the uniaxial ratchetting of SS316L stainless steel and 25CDV4.11 steel; but cannot simulate the ratchetting of 40Cr3MoV bainitic steel since the dependence of cyclic softening behaviours on the applied inelastic strain amplitude cannot be reasonably described in the discussed constitutive model. Some significant conclusions are obtained, which are useful to construct constitutive model to describe the ratchetting of the materials with different cyclic softening/hardening behaviours.     

A thermovisco-hyperelastic constitutive model of HTPB propellant with damage at intermediate strain rates

The uniaxial compressive tests at different temperatures (223–298 K) and strain rates (\(0.40\mbox{--}63~\mbox{s}^{-1}\)) are reported to study the properties of hydroxyl-terminated polybutadiene (HTPB) propellant at intermediate strain rates, using a new INSTRON testing machine. The experimental results indicate that the compressive properties (mechanical properties and damage) of HTPB propellant are remarkably affected by temperature and strain rate and display significant nonlinear material behaviors at large strains under all the test conditions. Continuously decreasing temperature and increasing strain rate, the characteristics of stress-strain curves and damage for HTPB propellant are more complex and are significantly different from that at room temperature or at lower strain rates. A new constitutive model was developed to describe the compressive behaviors of HTPB propellant at room temperature and intermediate strain rates by simply coupling the effect of strain rate into the conventional hyperelastic model. Based on the compressive behaviors of HTPB propellant and the nonlinear viscoelastic constitutive theories, a new thermovisco-hyperelastic constitutive model with damage was proposed to predict the stress responses of the propellant at low temperatures and intermediate strain rates. In this new model, the damage is related to the viscoelastic properties of the propellant. Meanwhile, the effect of temperature on the hyperelastic properties, viscoelastic properties and damage are all considered by the macroscopical method. The constitutive parameters in the proposed constitutive models were identified by the genetic algorithm (GA)-based optimization method. By comparing the predicted and experimental results, it can be found that the developed constitutive models can correctly describe the uniaxial compressive behaviors of HTPB propellant at intermediate strain rates and different temperatures.     

Super304H钢拉伸流变特性的研究

采用电液式万能试验机测试了奥氏体不锈钢Super304H在20～600℃、不同应变率下的流变应力和应变的关系。实验结果表明,应变速率和变形温度的变化强烈地影响Super304H钢的流变应力,在高温下出现明显的动态软化。根据得到的流变应力曲线,拟合出了JC模型和其修正的JC模型中的相关参数。经与实验对比验证,修正的JC本构模型能够很好地描述Super304H钢的动态力学性能,为生产工艺的制定和钢管质量的控制提供了重要的材料参数。     

A plastic shakedown constitutive curve based on uniaxial ratcheting behavior of 304 stainless steel at room temperature

On the basis of the Bauschinger effect, a relationship between the elastic space defined in this study and the accumulated plastic strain is measured in uniaxial ratcheting tests of 304 stainless steel at room temperature. According to this relationship, a new model of uniaxial ratcheting is established and used to simulate uniaxial ratcheting behavior. The results of simulation agree well with the experimental results. These results demonstrate that the relationship between the elastic space and the accumulated plastic strain plays an important role in uniaxial ratcheting simulation. Furthermore, by taking into account the interaction of ratcheting and viscoplasticity, the relationships among elastic space, accumulated plastic strain and loading cases are discussed. It can be seen that, when the stress ratio R of valley stress versus peak stress is not less than zero, the accumulated plastic strain is a function of the peak stress. So, a constitutive curve is obtained to describe the stable states of plastic shakedown for 304 stainless steel material under the stress ratio R ≥ 0. It can be used to determine the accumulated plastic strain of engineering structures under cyclic loading only by an elastic–plastic analysis.