有限弹塑性变形中应变及应变率的分解

本文对有限弹塑性变形中关于应变及应变率的分解问题进行了系统的评述。在讨论各派理论的基础上提出了我们的观点,并从缺陷场论角度研究了不协调塑性场的应变率分解。      

动—静态应变的红外遥测

本文介绍了动、静态应变测量的一种新方法－－红外遥测法的基本工作原理，操作方法及其几个有关技术问题。     

用光塑性技术求解两种应变定义的应变场

本文提出了用Almansi应变张量进行光塑性三维应变场求解的方法.为了便于工程应用,进一步提出了工程应变求解方法.用所提出的方法在连杆上进行了塑性成形后的变形场研究.     

中应变率下钢纤维混凝土受拉全过程实验研究

在简要评述有关中应变速率下钢纤维混凝土动态力学性能的实验研究现状后,详细介绍了在Instron1342材料实验机的基础上经自行改装设计的钢纤维混凝土动态测试系统,并对实验方案、试件制作与加载及量测过程进行了阐述。利用该系统,成功完成了应变率由1.38×10-4s-1～0.532×10-1s-1三个数量级范围内的钢纤维混凝土受拉全过程试验(四点弯拉),得到了中应变率下钢纤维混凝土的应力、应变全过程曲线。同时,对实验结果进行了综合分析,实验结果表明:中应变率下,应变率不同时钢纤维混凝土的应力应变全曲线具有很好的相似性,而峰值应力、峰值应变与弹性模量(割线模量)随应变率的增加均有不同程度的提高。当应变速率从1.38×10-4s-1增大到0.532×10-1s-1时,SFRC的抗拉强度提高30%左右,峰值应力对应的应变提高10%左右,动态拉伸弹性模量提高20%左右。中应变率(1.38×10-4s-1～0.532×10-1s-1)下,当钢纤维掺量从0%增加到4%时,钢纤维混凝土的抗拉强度提高1.3倍左右。     

应变疲劳强度概率分布

利用概率论方法建立了应变疲劳强度概率分布与应变疲劳寿命概率分布之间的数学关系式，并根据应变－寿命转换关系，由已知的给定应变水平下的疲劳寿命概率分布求出给定寿命下的应变疲劳强度分布函数，便于进行可靠性分析。     

温度场中应变光纤测试方法

研究温度变化时光纤应变测试系统中的传输光纤和感应光纤产生附加相位的问题推导出附加相位与温度变化的关系式，提出消除附加相位的补偿法通过实验分析证明了补偿法对消除附加相位是行之有效的，提高了测试精度     

在氢环境中钢的应变速率效应

从静态、准静态直到冲击的应变速率范围内(.ε=10-7~103sec-1),研究了在氢环境中应变速率对10钢力学性能的影响。结果表明:对于10钢,应变速率在3.33×10-3~3.33×10-6sec-1范围,氢的影响最明显,随着应变速率的提高或降低,氢的影响逐渐减弱;对于渗氢和未渗氢试样,应变速率在10-4~103sec-1范围内,屈服应力都随着应变速率的增加而增加,在.ε<6.0×102sec-1区域Ⅰ内流动应力与应变速率呈线性关系,在.ε>6.0×102sec-1区域Ⅱ内流动应力对应变速率十分敏感。与准静态时相比较,高应变速率下未渗氢试样的流动应力增加了1.1倍,而渗氢试样则增加了1.5倍。文中给出了可以精确描述10钢在高应变速率下渗氢与未渗氢试样的应力应变关系表达式。     

由应力集中处附近的应变值推求最大应力的一种方法

本文提出了一种用电阻片测定构件应力集中处最大应力的方案,以及相应的数据处理公式。典型实测与算例表明,本方法具有精度高的特点。并可以用于有限元、光弹性、云纹等方法。     

某种高温合金550℃高温应变测试

随着航空、航天技术的发展,飞行器热端部件的温度越来越高,载荷情况越来越复杂。为了更好地研究这些结构在高温环境下的力学特性,需要测试结构的高温应变并验证高温应变测试方法的可靠性。本文利用高温应变性能鉴定机测试四点弯曲高温合金梁在550℃稳态温度场条件下的高温应变。测试共进行三次,测试过程中温度的温升率为3℃/min。测试完成后,利用高温应变理论公式对高温应变试验数据进行处理,得到四点弯曲梁的真实应变值,并进行误差计算,四个应变片的误差分别为3%、20%、3%、7%,测试获得了较为满意的结果。此项试验结果表明:本文给出的四点弯曲高温合金梁高温应变测试方案合理可行,使用的高温应变计粘贴方案可靠性较高,四点弯曲梁高温应变测试方法可以作为今后进一步深入研究高温应变测试技术的参考资料和基础,为将来更高温度、更复杂的温度场环境下的高温应变测试提供技术支持。     

恶劣环境中应变测量的国内外发展综述

机器部件、构件和微电子元件,很多是在恶劣环境(包括高温、高压、低温、磁场、辐射、等离子体、腐蚀环境、高速旋转、液下等)中工作的。它们的力学破坏,对人们的安全和生产有非常不利的影响。为防止这些破坏,需要通过分析、实验和计算来改进设计、制造和检测,以提供减少破坏所必要的数据。实验力学,特别是在恶劣环境中进行力学测量,在此起了关键的作用。它提供了基本数据和检测手段,用于计算和建立破坏理论模型。本文介绍在恶劣环境中,主要在高温中,进行应变测量的国内外一些发展情况。     

Determination of elastic-plastic stresses and strains from measured surface strain data

A rigorous approach founded in the fundamental principles of plasticity is used to develop an accurate numerical algorithm for the determination of stresses and elastic and plastic strains from total strain data measured on a structure surface. The approach used to develop the algorithm and its relationship to both the flow theory of plasticity and recent advances in tangent stiffness-based numerical solution procedures for elastic-plastic boundary value problems are presented. Verification of the method for plane stress problems is demonstrated. A discussion of how the method can be used with measured surface displacement data is proved.     

基于线性互补模型的梯度塑性连续体无网格方法

对梯度塑性连续体提出了一个归结为线性互补问题的数值分析方法. 塑性乘子与位移均为主要未知变量,并采用基于移动最小二乘的无网格方法分别在积分点与节点上插值. 联立弱形式下的平衡方程与积分点上逐点满足的非局部本构方程和屈服准则可以导出一个线性互补问题,并通过Lexico-Lemke算法求解. 构造了一个基于N-R方法的迭代方案,使得不需要形成一致性切线刚度矩阵而仍保持二阶收敛性. 一维和二维的数值算例证明了所提出的方法处理由应变软化引起的应变局部化问题的有效性.      

Errors in crack closure measurements caused by flexure test fixture support effects

Flexural tests are sometimes used for the evaluation of fatigue and fracture properties, especially for thin cross sections such as plate material where compact tension speciments cannot be used, or where material thicness is limited in the direction required for data generation. The method is also useful for evaluation of crack closure provided the force transfer occurs correctly. This paper shows how the influence of incorrect test fixture supports, which are outside the standard testing arrangement for such test specimens, can affect the force-displacement curves as evidenced using the backface strain method. The results show that incorrect test fixture supports may cause deviations in the force-displacement trace as an artifact of the testing conditions. This effect can severely influence crack closure measurements. The effect was also modeled with finite element analysis.     

应变空间中的弹塑性数值计算方法

本文论述了应变空间表述的岩土弹塑性理论及其数值计算方法的有关问题,并按此编制了计算程序.所给算例表明这一方法是简便可行的,为解决岩土工程问题提出了一种更好的途径.     

A more comprehensive method for yield locus construction for metallic alloys and composites

Conventional methods for constructing yield loci rely on the assumption that nonlinear strains are permanent strains, which is not always the case. A nickel-base alloy, SiC fiber-reinforced titanium, an aluminum alloy, and particlereinforced aluminum have been observed to violate this assumption. We present a method for constructing yield loci using a proof strain criterion for the permanent strain that relies on cyclic, proportional, probes of the yield surface. Two criteria are implemented: one for stress reversal and one for yielding. The method is demonstrated by the construction of initial and subsequent yield loci in the axial-shear stress plane using thin-walled tubular specimens. Results are presented for 6061-T6 aluminum as well as for 6092/SiC/17.5p-T6, which is 6092 aluminum reinforced with 17.5 volume percent silicon carbide particulate. The centers of the initial yield loci for the composite are eccentric to the origin of the stress plane most likely because of the residual stresses induced during processing. Material hardening due to multiaxial stress states can be described by tracking evolution of the subsequent yield surfaces and here hardening of the particulate composite was primarily kinematic     

A combined parametric quadratic programming and precise integration method based dynamic analysis of elastic-plastic hardening/softening problems

The objective of the paper is to develop a new algorithm for numerical solution of dynamic elastic-plastic strain hardening/softening problems. The gradient dependent model is adopted in the numerical model to overcome the result mesh-sensitivity problem in the dynamic strain softening or strain localization analysis. The equations for the dynamic elastic-plastic problems are derived in terms of the parametric variational principle, which is valid for associated, non-associated and strain softening plastic constitutive models in the finite element analysis. The precise integration method, which has been widely used for discretization in time domain of the linear problems, is introduced for the solution of dynamic nonlinear equations. The new algorithm proposed is based on the combination of the parametric quadratic programming method and the precise integration method and has all the advantages in both of the algorithms. Results of numerical examples demonstrate not only the validity, but also the advantages of the algorithm proposed for the numerical solution of nonlinear dynamic problems. The project supported by the National Key Basic Research Special Foundation (G1999032805), the National Natural Science Foundation of China (19872016, 50178016, 19832010) and the Foundation for University Key Teacher by the Ministry of Education of China     

高分辨率电镜微米云纹法及其应用

文中就云纹干涉法,电子束云纹法,原子力云纹法,扫描电镜云纹法,聚焦离子束云纹测量微区变形的原理和适用性进行了讨论.应用1200线/毫米的云纹光栅并结合云纹干涉法,电子束云纹法,原子力云纹法,扫描电镜云纹法测量QFP和BGA型电子封装组件的热变形.提出一种新型聚焦离子束云纹法,在MEMS结构上制栅形成FIB扫描云纹,成功的实验结果表明这种方法的可行性.     

云纹干涉法瞬态应变分析

本文将单光束错位云纹干涉法应用于动态测量,获得了一种可独立求解全场瞬态应变分量,不受材料限制的动态测量新方法。文中应用该方法对一个受冲击载荷的带也孔方板的动态应变传播过程及对称面上的动应变分布进行了研究,得到了比较理想的结果。