应变硬化水泥基复合材料单轴滞回本构模型

为了有效地模拟应变硬化水泥基复合材料(SHCC)构件在地震作用下的性能,提出一种可模拟SHCC构件在反复荷载作用下的单轴本构模型.该模型中SHCC材料受压骨架曲线的上升段采用二次抛物线形式模拟,下降段采用双折线形式模拟;受拉骨架曲线的上升段、应变硬化段及下降段则采用三折线形式模拟.通过设置参考点的方法确定SHCC的卸载规则,考虑了不完全卸载-再加载的情况以及加载过程中的拉压间的传递模式.利用Open SEES计算平台编写了该本构模型,并与材料和构件2个层次的试验结果进行了对比,结果表明,所提出的单轴滞回模型能够准确地反映SHCC材料在反复荷载作用下的受力性能.     

低温下钢材应变强化系数的测定

设计了在低温下不用引伸计测定钢材应变强化系数ｎ值的方法，在系列温度下测定了１６ＭｎＲ，４０ＣｒＮｉＭｏ和ＷＣＦ６２三种钢材的ｎ值，发现材料的ｎ值随试验温度的降低而下降，其部分原因是由于屈服强度的升高使材料的应变强化能力相对下降．实验结果还表明按幂强化关系来描述材料应变强化规律的Ｈｏｌｌｏｍｏｎ关系和Ｒａｍｂｅｒｇ－Ｏｓｇｏｏｄ关系，在工程意义上可认为是相同的．     

几种不锈钢的拉伸应变硬化行为

采用金相、X射线衍射(XRD)、拉伸试验和洛氏硬度检测等实验方法,研究4种不锈钢(410S、430、409L和304)的室温拉伸应变硬化行为,探讨其拉伸应变行为的特征与规律.结果表明:304不锈钢的加工硬化能力远高于410S、430、409L不锈钢.而且304冷轧(固溶)态的n值(0.57)高于304热轧(空冷)态n值...     

Stress-state dependence of dynamic strain aging: Thermal hardening and blue brittleness

This study aims to discover the stress-state dependence of the dynamic strain aging(DSA) effect on the deformation and fracture behavior of high-strength dual-phase(DP) steel at different deformation temperatures(25–400℃) and reveal the damage mechanisms under these various configurations. To achieve different stress states, predesigned specimens with different geometric features were used. Scanning electron microscopy was applied to analyze the fracture modes(e.g., dimple or shear mode) and underlying damage mechanism of the investigated material. DSA is present in this DP steel, showing the Portevin–Le Chatelier(PLC) effect with serrated flow behavior, thermal hardening, and blue brittleness phenomena. Results show that the stress state contributes distinctly to the DSA effect in terms of the magnitude of thermal hardening and the pattern of blue brittleness. Either low stress triaxiality or Lode angle parameter promotes DSA-induced blue brittleness. Accordingly, the damage mechanisms also show dependence on the stress states in conjunction with the DSA effect.     

动态应变时效的应力状态依赖性:热硬化和蓝脆

This study aims to discover the stress-state dependence of the dynamic strain aging (DSA) effect on the deformation and fracture behavior of high-strength dual-phase (DP) steel at different deformation temperatures (25–400°C) and reveal the damage mechanisms under these various configurations. To achieve different stress states, predesigned specimens with different geometric features were used. Scanning electron microscopy was applied to analyze the fracture modes (e.g., dimple or shear mode) and underlying damage mechanism of the investigated material. DSA is present in this DP steel, showing the Portevin–Le Chatelier (PLC) effect with serrated flow behavior, thermal hardening, and blue brittleness phenomena. Results show that the stress state contributes distinctly to the DSA effect in terms of the magnitude of thermal hardening and the pattern of blue brittleness. Either low stress triaxiality or Lode angle parameter promotes DSA-induced blue brittleness. Accordingly, the damage mechanisms also show dependence on the stress states in conjunction with the DSA effect.     

一种非共轴应变硬化本构模型数值应用及离心机试验验证

在土体的剪切变形过程中,当主应力方向产生旋转时,主应变增量方向与主应力方向之间存在显著的非共轴现象.同时,机动摩擦角、膨胀角随着累积塑性偏应变的增长而增加,土体具有应变硬化的特点.传统的弹塑性本构模型不能够反映上述现象对地基承载力特性的影响.为了能够对地基承载力问题进行合理的分析,建立了一种非共轴应变硬化模型,并将该模型运用到有限元计算中.通过与三轴试验和离心机模型试验结果进行对比,对该模型在数值应用中的合理性进行了验证.研究结果表明,该模型能够对不同围压下的应力-应变关系进行预测.对浅基础承载力问题进行研究时,非共轴应变硬化模型的计算结果比传统弹塑性本构模型更加接近于离心机试验结果,验证了该模型的数值应用合理性.     

Damage evolution model of strain hardening cementitious composites under the uniaxial stress state

The deformation and damage behaviors of strain hardening cementitious composites (SHCC) under the uniaxial stress state were investigated in this paper. Two ductile failure-based constitutive models were introduced to describe the uniaxial tension and compression properties of SHCC only using a few parameters. The computation method of model parameters was developed to ease the simulation procedures. Damage evolution of the SHCC was simulated by the formulation of continuum damage mechanics subsequently. The results show that the proposed models fit the stress-strain curves reasonably well, and the damage variables show different growth rules under uniaxial tension and compression. It is concluded that the proposed method can not only simply simulate the constitutive behavior of SHCC with the reasonable accuracy but also capture the characteristic of material degradation.     

小应变土体硬化模型参数的敏感性分析及确定方法

小应变土体硬化(Hardening soil model with small strain stiffness, HSS)模型能够反映土体小应变阶段的非线性特性和应力相关性,在深基坑工程领域已被广泛应用,但由于参数众多,目前对参数确定方法尚缺乏系统研究。分析了HSS模型各参数的意义及常规确定方法,采用数值模拟方法开展了HSS模型参数的敏感性分析,基于统计的大量研究成果,建立了土体参数与孔隙比之间的非线性关系,进一步通过2处深基坑工程的变形分析进行验证。结果表明：在基坑数值分析中,参考动剪切模量 的敏感性最高,参考切线模量 的敏感性最低,建立的非线性关系能够较好的反映土体模量与孔隙比的相关性,围护结构侧移的计算值及实测值较为吻合,验证了提出的参数确定方法的适用性,可为相关工程提供参考。     

AISI 321奥氏体不锈钢的应变硬化行为、应变速率敏感性及热变形图

Hot compression tests were performed on AISI 321 austenitic stainless steel in the deformation temperature range of 800–1200°C and constant strain rates of 0.001, 0.01, 0.1, and 1 s?1. Hot flow curves were used to determine the strain hardening exponent and the strain rate sensitivity exponent, and to construct the processing maps. Variations of the strain hardening exponent with strain were used to predict the microstructural evolutions during the hot deformation. Four variations were distinguished reflecting the different microstructural changes. Based on the analysis of the strain hardening exponent versus strain curves, the microstructural evolutions were dynamic recovery, single and multiple peak dynamic recrystallization, and interactions between dynamic recrystallization and precipitation. The strain rate sensitivity variations at an applied strain of 0.8 and strain rate of 0.1 s?1 were compared with the microstructural evolutions. The results demonstrate the existence of a reliable correlation between the strain rate sensitivity values and evolved microstructures. Additionally, the power dissipation map at the applied strain of 0.8 was compared with the resultant microstructures at predetermined deformation conditions. The microstructural evolutions strongly correlated to the power dissipation ratio, and dynamic recrystallization occurred completely at lower power dissipation ratios.     

Strain hardening behavior,strain rate sensitivity and hot deformation maps of AISI 321 austenitic stainless steel

Hot compression tests were performed on AISI 321 austenitic stainless steel in the deformation temperature range of 800–1200°C and constant strain rates of 0.001, 0.01, 0.1, and 1 s~(-1). Hot flow curves were used to determine the strain hardening exponent and the strain rate sensitivity exponent, and to construct the processing maps. Variations of the strain hardening exponent with strain were used to predict the microstructural evolutions during the hot deformation. Four variations were distinguished reflecting the different microstructural changes. Based on the analysis of the strain hardening exponent versus strain curves, the microstructural evolutions were dynamic recovery, single and multiple peak dynamic recrystallization, and interactions between dynamic recrystallization and precipitation. The strain rate sensitivity variations at an applied strain of 0.8 and strain rate of 0.1 s~(-1) were compared with the microstructural evolutions. The results demonstrate the existence of a reliable correlation between the strain rate sensitivity values and evolved microstructures. Additionally, the power dissipation map at the applied strain of 0.8 was compared with the resultant microstructures at predetermined deformation conditions. The microstructural evolutions strongly correlated to the power dissipation ratio, and dynamic recrystallization occurred completely at lower power dissipation ratios.     

磁致塑性的位错机理

采用佩尔斯-纳巴罗的部分离散位错模型,计算了磁场中直刃型位错的错排能,推导出在静磁场中位错滑移所需克服晶体点阵阻力的最大值--佩-纳力,给出了佩-纳力与磁场强度、材料性质间的关系.结果表明:若材料中的位错具有顺磁性,佩-纳力的值比无磁场时的值减少,位错更容易运动,材料塑性增强.该结论与已有的磁塑效应实验中观察到的现象一致.当磁场为0时,所得佩-纳力的值可退化为已知的原佩-纳力.     

CSP工艺热轧低碳带钢位错形貌及密度分析

采用H-800透射电子显微镜及正电子湮没技术，观察了CSP工艺热轧低碳带钢轧制过程中位错形貌，并计算了终轧后轧件的位错密度，结果表明：随着轧制过程的进行，累积变形量的增加，位错密度逐渐提高，CSP工艺比传统工艺生产的同规格产品位错密度高约一个数量级。     

加载速率对位错发射、层错宽度及位错速度影响

应用分子动力学方法研究了Ｃｕ和Ａｌ单晶在Ⅱ型加载条件下，加载速率对位错发射、层错宽度Ｗ及位错速度Ｖｄ的影响。结果表明，加载速率对Ｗ和Ｖｄ有显著影响。随着加载速率的增大，层错宽度减小，位错速度增大。当加载速率达到某一临界值时，能量不仅以发射位错的形式释放，而且形成孪晶，以降低体系的能量。     

磨球淬硬深度的预测

利用有限差分方法和传热方程对端淬试样及磨球淬火冷却过程的温度场进行了计算,给出了端淬试样及磨球不同位置从800℃降到400℃的平均冷却速度.建立了两者间相同冷却速度的位置对应关系,从而利用端淬试样的硬度分布预测磨球的硬度分布.对制备的直径50~100 mm试验钢磨球淬火硬度与计算结果进行对比,二者吻合较好.     

服务行政:理念及其实践错位

服务行政是政府公共部门在运行和发展中遵循“顾客至上”理念、以回应“公民需求”,实现“公民”公共利益为目标的新型治理模式。服务行政与传统行政最大的区别在于它的服务性、公民本位和社会本位。然而,服务行政在实现为公众服务的宗旨,履行服务的职能时,在一些特殊的条件下,却有可能背离其本意。出现实践的错位。     

新闻教育必须与新闻学科错位

新闻教育的核心要体现新闻主体思维机制的建构，社会也以此衡量新闻教育存在的必要性，衡量它是否有利于为人类建立最佳舆论生态并可持续健康地生存、发展。在新闻报道传播中，再离奇的新闻传达的也是对常情常理的回归，所谓“意料之外，情理之中”。新闻情理就是对常情常理的强调，而新闻传播专业研究中常情常理就没有学科研究价值，因此，新闻教育内容必须与新闻研究对象适当错位。     

Bake hardening behavior of TRIP and DP steels

The bake hardening (BH) behavior of transformation-induced plasticity (TRIP) and dual-phase (DP) steels after different prestrains was studied. The experimental results indicate that TRIP steel exhibits good BH ability while DP steel does not, and prestrain displays a strong effect on the BH values of both steels. The comparison of microstructures of the two steels showed that the hard second phase in the matrix might be harmful to the BH ability. For deformed specimens, baking resulted in a loss of uniform elongation, but there was no obvious decrease in uniform elongation for unprestrained specimens.     

双位错滑移运动的晶体相场模拟

【目的】研究晶体位错运动对材料加工力学性能的影响。【方法】应用改进晶体相场(Phase-field-crystal,PFC)模型,研究剪切应变作用下晶体的双位错的滑移运动特征。【结果】在应变作用下,体系的双位错只作滑移运动,运动方向平行且相反,保持匀速运动,不出现攀移运动;应变率较小时,位错作滑移运动,越过势垒需要一定孕育时间,此时滑移出现颠簸式运动特征;应变率较大时,位错滑移运动呈匀速直线运动。【结论】PFC模型能较好地用于研究位错在应变作用下的运动。