静止裂纹尖端实验的HRR奇异场

用近代光学试验方法(面内云纹和投影云纹),测量了不同应变硬化指数材料(n=3.350～9.180)、平面应力Ⅰ型双边裂纹试件、裂纹尖端附近位移场和应变场。由试验结果分析了裂纹尖端位移奇异性,得到J主导区和围绕裂纹尖端附近HRR场分布。分析了HRR分布随载荷、材料不同的变化规律。     

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。     

金属材料单轴拉伸变形规律的研究

本文对五种钢和四种高温合金的单轴拉伸变形规律进行了研宄.结果表明:在均匀变形阶段,大多数材料的应力应变关系分段地服从幂乘律σ=εn,但硬化指数n并不等于最大均匀真应变εu;在不均匀变形阶段,应力应变关系多服从线性律.本文测定出七种材料在不均匀变形阶段缩颈曲率半径R随(ε-εu)的变化规律,证实了a/R∝(ε-εu),比例系数在0.6-1之间.     

一维六方准晶压电材料含运动螺型位错弹性问题分析

借助复变函数方法,研究了点群6mm一维六方准晶压电材料中运动螺型位错,得到位错芯附近的应力、位移、能量的解析表达式。分析发现,在靠近运动螺型位错芯处,声子场和相位子场应力的分量表现出(x²+y²)^-1的奇异性。当不考虑相位子场的影响时,文中得到的结果可以退化为含运动螺型位错的压电材料中的结果;当不考虑电场的影响时,退化得到的结果与准晶材料中含运动的螺型位错一致;当v=0时,可还原为静态螺型位错的解析解。     

剪切力作用下螺位错的运动

利用分子动力学方法研究了金属钨中螺位错在剪切力作用下的运动特性.根据弹性理论在BCC晶体中形成位错线沿<111>的螺位错,在合适的边界条件下获得平衡态的位错结构.发现位错由{110}平面沿<112>方向三个呈对称的皱褶组成.对平衡态结构施加剪切力,发现剪力很小时,位错核心不动,核心形状有畸变;当剪力增大到一定程度时位错开始运动.位错运动后,剪切力较小时,核心呈“之”字形运动;在较大剪力下,位错开始阶段呈“之”字形运动,一段距离后主要沿[211]方向作直线运动.位错运动的速度随着剪切力的增加而增大.     

基于初始应变变化的自组装螺旋变形有限元分析

螺旋结构是自然界和工程应用中的基本形态,在不同几何和力学条件下可实现多种形态间的相互转变。本文以双层薄弹性材料结构模型为例(长度L>>宽度W>>厚度H),利用层间存在的不同初始应变,采用三维有限元模拟方法,分析了结构的形态转变情况。结果表明:当加载单层预应变(ε1=0.25)时,改变几何主轴和初始应变主轴方向间的错配角φ,可实现弹性带在圆环、螺旋形、不完整柱形间相互转变;当加载双层预应变(ε1=-ε2=0.25)时,同时改变几何错配角,可实现弹性带在"轮毂"形、纯扭转、一般扭转间的自组装螺旋相互转变。     

NiTi形状记忆合金动态压缩力学行为的实验研究

采用材料试验机和SHPB实验技术,对在不同初始温度(298～873K)和应变率(5×10-4、～2.3×103s-1)下的NiTi形状记忆合金的压缩力学行为进行了实验研究。结果表明:马氏体状态下的NiTi合金的力学行为对应变率的变化敏感,位错屈服段的硬化模量、相屈服段的硬化模量及马氏体重取向前的弹性模量对应变率的变化不敏感,而位错塑性变形前的弹性模量随应变率的提高迅速增大;奥氏体状态下的NiTi合金随着实验温度升高,无论是应力诱发马氏体相变应力还是奥氏体相屈服应力都逐渐下降,材料表现出温度软化效应。从超弹性温度范围内的卸载曲线中观察到了应力诱发马氏体到奥氏体的逆转变。     

单畴外延铁电薄膜的相结构与稳定性

本文采用动态金茨堡-朗道（DGL）方程研究了薄膜厚度与错配应变对 取向单畴外延PbTiO3（PTO）铁电薄膜相结构与稳定性的影响。结合平面内松弛应变（等效应变）、表面效应与退极化场等机电耦合边界条件,通过数值求解DGL方程获得外延单畴铁电薄膜错配应变-厚度相图和错配应变-温度相图。数值分析结果显示,由于生成的界面位错松弛了薄膜内错配应变,在理论高应变区相图与传统分析结果有较大差别,文中发现在更广的理论错配拉应变区出现稳定的四方相（c相）结构和单斜相（r相）结构。结果也显示,随着薄膜厚度的减小,表面效应与退极化效应会把顺电相扩展到更低温度区域,从而压缩稳定的铁电相存在的温度区域。     

一种基于位错机制的动态应变时效模型

动态应变时效是由位错与溶质原子的相互作用引起的，只考虑位错与位错芯内的溶质原子（位错芯气团）的相互作用，在位错热激活运动机制的Zerilli-Armstrong热粘塑性本构模型的基础上，加以改进，并加入位错和位错芯片团的相互作用的影响，建立了一种可定量描写动态变变时效现象的本构模型，所得到的本构模型以Zerilli-Armstrong模型为基础，不仅可以描写动态应变时效现象，还可以描写金属在很大温度（77K－1000K）和应变率（10^-4-10^4s^-1)范围内的力学行为，本构模型对钽的拟合和预测与实验结果有较好的吻合。     

孪生诱发塑性对V-5Cr-5Ti合金应变硬化行为的影响

钒合金(V-Cr-Ti)作为潜在重要的聚变反应堆用结构材料, 近年来受到广泛的关注. 为了研究 V-5Cr-5Ti 合金不同应变率压缩下的应变硬化行为, 特别是孪生对塑性变形的影响, 以位错密度和孪晶演化为基础, 建立了该合金的应变硬化模型. 模型中考虑了孪晶中的位错滑移对材料塑性应变的贡献. 模拟结果表明, 由于孪生诱发塑性, 从而使动态压缩时的位错密度小于准静态加载时的, 这使得 V-5Cr-5Ti 合金在动态压缩时的应变硬化率比准静态加载时的小. 当孪晶形成后, 位错滑移引起的塑性应变率随应变增大而增大, 并逐渐接近加载应变率, 而孪生引起的塑性应变率则随应变增大而减小.      

激光选区熔化增材制造GP1不锈钢动态拉伸力学响应与层裂破坏

采用选择性激光熔化增材制造技术，制备了GP1不锈钢单轴拉伸板条试样和层裂圆片试样，并对材料微观结构进行了表征。借助Zwick-HTM5020 高速拉伸试验机，并结合数字图像相关性全场应变测量技术，开展了增材制造GP1不锈钢材料的轴向拉伸力学性能实验研究，得到了不同应变率下材料的拉伸应力-应变曲线，结果显示:(1) GP1不锈钢流动应力具有比较显著的应变强化效应；(2)通过回收试样的电子背散射衍射表征，发现GP1不锈钢在拉伸变形过程中会发生奥氏体与马氏体之间的相变；(3) GP1不锈钢的屈服应力随着应变率呈幂指数增大，断裂应变在中低应变率下保持不变，但在高应变率下则显著减小。采用一级轻气炮实验装置和激光干涉粒子速度测量技术，开展了增材制造GP1不锈钢的层裂实验，发现GP1不锈钢的层裂强度随着飞片撞击速度增大而减小。单轴拉伸试样断口和层裂试样断口的显微分析结果表明:随着应变率增大，单轴拉伸断裂模式和断裂机理都发生了转变；层裂损伤易成核于激光熔池边界线的交汇处，断口韧窝形貌明显区别于单向拉伸断口。     

新型铝锡硅合金高温塑性变形流变应力的研究

采用高温等温压缩变形方法,在温度为373-673K范围和应变速率为0.001-1.0s^-1范围内,测定了新型Al-10Sn-4Si合金的流变应力曲线,结果表明,该合金为正应变速率敏感材料并且具有稳态流变特征;稳态流变应力随变形速率的增加而增大,随变形温度的升高而降低,通过回归分析,建立了该合金高温塑性变形时稳态流变应力的半经验方程,这种稳态流变特征与动态回复、动态再结晶及局部晶界粘滞性流动行为有关,受热激活过程控制。     

Flow stress behavior of porous FVS0812 aluminum alloy during hot-compression

The hot deformation behavior of porous FVS0812 aluminum alloy prepared by spray deposition was studied by means of compression tests on a Gleeble 1500 machine. The samples were hot compressed at temperatures ranging from 573 K to 773 K under various true strain rates of 10⁻⁴–10⁰ s⁻¹. The deformation behaviors are characterized by a significant strain hardening during hot-compression due to the progressive compaction of the pores with increasing compressive strain. A revised formula describing the relationships of the flow stress, strain rate and temperature of the porous alloy at elevated temperatures is proposed by compensation of strain. The theoretical predictions are compared with experimental results, which show good agreement.     

ARB过程中β钛基SMA显微结构演化及对其超弹性能的影响

本文采用复合轧制（Accumulative Roll-Bonding，ARB）工艺对β钛基形状记忆合金(SMA)进行轧制，然后700℃下快速热处理（保温5min）。利用光学显微镜（OM）和X射线衍射仪（XRD）对合金轧制热处理前后合金相组成与显微组织进行分析，并用电子万能试验机对轧制试样的力学性能和超弹性能进行测试。研究了β钛基形状记忆合金复合轧制过程中显微结构演化规律及对其超弹性能的影响。结果表明：复合轧制工艺能有效细化合金晶粒，经过轧制8道次、700℃/5min快速热处理可得到全β相合金组织，其晶粒尺寸1μm；复合轧制处理后合金的超弹性能得到了改善，在预变形为6%时，其回复变形为5.94%，回复率为99%，表现出稳定的超弹性。     

ARB过程中β钛基SMA显微结构演化及对其超弹性能的影响

本文采用复合轧制（Accumulative Roll-Bonding,ARB）工艺对β钛基形状记忆合金(SMA)进行轧制,然后700℃下快速热处理（保温5min）。利用光学显微镜（OM）和X射线衍射仪（XRD）对合金轧制热处理前后合金相组成与显微组织进行分析,并用电子万能试验机对轧制试样的力学性能和超弹性能进行测试。研究了β钛基形状记忆合金复合轧制过程中显微结构演化规律及对其超弹性能的影响。结果表明：复合轧制工艺能有效细化合金晶粒,经过轧制8道次、700℃/5min快速热处理可得到全β相合金组织,其晶粒尺寸1μm;复合轧制处理后合金的超弹性能得到了改善,在预变形为6%时,其回复变形为5.94%,回复率为99%,表现出稳定的超弹性。     

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.     

An experimental investigation of a superplastic constitutive equation in Al–Mg–Si alloy composites reinforced with Si3N4 whiskers

Superplastic properties at 818 K were investigated by tensile tests for Al–Mg–Si alloy composites reinforced with Si₃N₄ whiskers whose volume fractions were 0–30%. The 20 and 30 vol.% composites exhibited large elongation of 615 and 285% at a high strain rate of 2×10⁻¹ s⁻¹, respectively. High strain rate superplasticity of the composites is attributed to the very small grain size of less than 3 μm. The stress–strain rate relation for the composites was almost the same as that of the alloy, taking into consideration the influences of threshold stress and grain size, and the relation was independent of the volume fraction of whisker. This is probably because grain boundary sliding was not hampered by the whiskers due to the presence of liquid phase for the composites.     

Crystal plasticity-based forming limit prediction for non-cubic metals: Application to Mg alloy AZ31B

A viscoplastic crystal plasticity model is incorporated within the Marciniak–Kuczynski (M–K) approach for forming limit curve prediction. The approach allows for the incorporation of crystallographic texture-induced anisotropy and the evolution of the same. The effects of mechanical twinning on the plastic response and texture evolution are also incorporated. Grain-level constitutive parameters describing the temperature dependent behavior of hexagonal close packed Mg alloy, AZ31B, sheets at discrete temperatures are used as a first application of the model. A trade-off between significant strain hardening behavior at lower temperatures (∼150 °C), and significant strain rate hardening at higher temperatures (∼200 °C) lead to similarities in the predicted forming limits. The actual formability of this alloy depends strongly on temperature within this range, and this distinction with the current modeling is related to more localized instability-based failure mechanisms at the lower temperatures than is assumed in the M–K approach. It is shown that the strain path dependence in the strain hardening response is significant and that it influences the forming limits in a predictable way. For broader applicability, a means of incorporating dynamic recrystallization into the crystal plasticity model is required.     

应变幅值对循环载荷下NiTi合金力学性质的影响

实验研究了应变幅值对循环载荷下NiTi合金伪弹性退化特征的影响规律,结果表明:当卸载发生在NiTi合金应力诱发马氏体相变阶段时,应变幅值对马氏体相变开始应力的退化规律影响较小,但此时应变幅值的增加会显著增大奥氏体弹性模量的退化程度,而其大变形可回复能力和阻尼特性在应变幅值大于6%时才有大幅度降低。对各参数退化程度进行定量分析,得到了NiTi合金具有较强可回复能力和阻尼性能的应变幅值范围。该研究可为NiTi合金阻尼器的设计提供参考。     

The characteristics of plastic flow and a physically-based model for 3003 Al–Mn alloy upon a wide range of strain rates and temperatures

The uniaxial compressive responses of 3003 Al–Mn alloy upon strain rates ranging from 0.001/s to about 10⁴/s with initial temperatures from 77 K to 800 K were investigated. Instron servohydraulic testing machine and enhanced split Hopkinson bar facilities have been employed in such uniaxial compressive loading tests. The maximum true strain up to 80% has been achieved. The following observations have been obtained from the experimental results: 1) 3003 Al–Mn alloy presents remarkable ductility and plasticity at low temperatures and high strain rates; 2) its plastic flow stress strongly depends on the applied temperatures and strain rates; 3) the temperature history during deformation strongly affects the microstructure evolution within the material. Finally, paralleled with the systematic experimental investigations, a physically-based model was developed based on the mechanism of dislocation kinetics. The model predictions are compared with the experimental results, and a good agreement has been observed.