推求应力集中处最大应力的确切值

本文提出一种由应力集中处附近已知的三点应力或应变值推求最大应力值的方法.实例表明,精度较高,使用简便.     

一种测试动态应力集中的灰色建模方法

将灰色系统方法理论中的GM（1,1）模型,应用于动态应力集中测试的数据处理,根据应力集中处附近的应变测试值,能方便地求出应力集中处的最大应变值。结果表明,该方法简单,预测精度较高,应用方便。     

力电耦合载荷作用下铁电陶瓷破坏行为的云纹干涉方法研究

本文介绍了如何用云纹干涉法实时地观察铁电陶瓷在力载荷和电载荷共同作用下裂尖的破坏行为．测量了三点弯试验中由电场和应力集中导致的裂尖的变形场．对变形的云纹图分析表明：当极化方向与裂纹扩展方向一致，且都与电场方向垂直，裂尖附近的正应变随电场的增加而增加，应变集中现象比较突出，电场促进和加速了裂纹的扩展．     

硬化材料切口根部应力--应变集中与理论应力集中的关系

以含浅切口的硬化材料为对象，以平面应变条件下切口根部附近的应力-应变分布为出发点，利用应力平衡法，研究了Neuber准则及Moski-Glinka公式的有效性。发现无论是Neuber准则还是Moski-Glinka公式，都没能很好地反映切口根部的应力-应变集中与理论应力集中的关系。因此，本文作者综合Neuber准则及Moski-Glinka公式，提出了一个更能正确反映切口根部应力-应变集中与理论应力集中关系的表达式。     

高地应力下大型地下洞室拱形优化研究

高地应力区的大型洞室开挖会引起洞室拱周附近围岩应力集中和塑性区加大以及塑性应变的增加，但过高的应力集中会增加岩爆发生的几率，塑性区的加深会促使围岩失稳；洞室拱形形状会影响围岩应力集中和塑性区大小的分布，因此，以某高地应力下的大型发电洞岩体地质资料为依托，用弹塑性有限元分析高地应力地下大型发电洞室常采用的3种洞室拱形（即单心圆拱、三心圆拱和椭圆拱）对拱部围岩应力的影响，计算结果表明这种影响是非常明显的，有的应力集中系数达到3．33，无论采用哪种拱形，均避不开拱座附近应力集中现象。根据开挖后拱部围岩的塑性耗散能可以判断，无论初始地应力侧压系数是多少，椭圆拱是最优的，其次是三心圆拱。     

弹性带形域中多个半圆柱形凹陷对SH波的散射

对稳态SH（shear horizontal）导波在表面含有多个半圆柱形凹陷的弹性带形介质内的散射问题进行了研究，并给出了解析解。首先，运用导波展开法构造平面SH导波；然后，利用累次镜像法构造出满足带形域上、下两条直边界应力自由条件的散射波；最后，根据凹陷边沿的切应力为零的条件得到定解方程。通过算例分析了累次镜像法的精度、凹陷边沿的动应力集中和上、下边界位移幅值的变化情况。数值结果表明:只有一个凹陷时，中高频率的入射波和小厚度的带形域会引起凹陷边沿更高的动应力集中，上边界位移幅值的最大值会出现在凹陷的迎波面附近；当有两个凹陷时，大多数情况下，第二个凹陷对第一个凹陷边沿的动应力集中起放大作用，并且在理想弹性带形介质内，两凹陷之间的影响在相距无穷远时也会存在。     

关于多轴疲劳寿命临界面法影响因素的分析与计算

本文以拉-扭非比例加载下的薄壁圆管试件为研究对象,以最大法向应变的最大剪应变平面为临界面,并对此临界面上的应变状态进行了分析。采用统一型疲劳寿命预测模型,以正火45钢为例,研究了非比例加载时相位差对疲劳寿命的影响,进而对不同正应变幅和应变幅值比加载下的危险相位差的变化规律进行了计算分析。结果发现:应变幅值比对疲劳寿命最短时的危险相位差的影响呈先上升后下降的趋势;并给出了不同应变幅值比时危险相位差的计算通式,式中的系数可通过材料力学性能与单轴疲劳参数计算得到。最后给出了15种材料的系数供实际应用时参考。     

人工神经网络用于识别受内压弹塑性圆管内壁腐蚀的反问题

为确定因腐蚀，圆管内壁几何形状的改变，可通过观察外壁若干点在工作内压下发生的弹塑性应变值，用三层人工神经网络作逆分析。该网络则是由计算力学提供在不同内壁半径和偏心距时的多组应变值进行学习，计算机数值实验表明，这种方法是有效的，识别内壁几何参数有相当的精度。     

采用显微网格法研究韧性材料平面应力状态下裂尖附近的应变场

用显微网格数字图象处理方法，测量了韧性材料平面应力条件下Ｉ型单边裂纹尖端附近的应变场。实验结果表明：在裂尖两侧存在与裂纹方向夹角约为５０°的大变形带。最大应变位于离裂尖一定距离的大变形带上，随着载荷增加，最大应变的位置逐渐靠近裂纹尖端。应变峰值轨迹线在裂纹顶端呈放射状，载荷增加时，应变峰值的轨迹线位置并不改变。     

动态起裂韧性测试过程的三维分析

本文应用线性弹性动脉有限元分析方法，对利用ＨＯＰＫＩＮＳＯＮ压杆技术测试材料动态起裂韧性的试验过程进行了三维数值计算，求得了加载波入，加载点位移，试样裂尖动脉应力强度因子，裂尖附近点应变历程以及材料动态起裂韧性值，并与实验－数值方法所得的各结果进行了比较分析。     

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。     

A Maximum Likelihood Method for Estimating Probabilistic Strain Amplitude-Fatigue Life Curves

The fatigue lives of materials and structures at different strain levels show heteroscedasticity. In addition, when the number of test specimens is insufficient, the fatigue strength coefficient and fatigue ductility coefficient of the fitting parameters in the total strain life equation may not have definite physical significance. In this work, a maximum likelihood method for estimating probabilistic strain amplitude-fatigue life curves is presented based on the fatigue lives at different strain levels. The proposed method is based on the general basic assumption that the logarithm of fatigue life at an arbitrary strain level is normally distributed. The relationship among the parameters of total strain life equation, monotonic ultimate tensile stress and percentage reduction of area is adopted. The presented approach is finally illustrated by two applications. It is shown that probabilistic strain amplitude-fatigue life curves can be easily estimated based on the maximum likelihood method. The results show that fatigue lives at different strain levels have heteroscedasticity and the values of fatigue strength coefficient and fatigue ductility coefficient obtained by the proposed method are close to those of the true tensile fracture stress and true tensile fracture strain.     

韧性金属裂纹尖端损伤区内应变场测量——数字散斑相关法应用

本文用数字散斑相关方法测量了五种不同幂硬化指数韧性金属材料(铝和铜),双边裂纹尖端细观区域内应变场.对所得结果用韧性损伤模型进行了分析.在此法中以金属自然表面结构为散斑场,不同加载状态的散斑场进行比较,得到相对变形与应变.图象之间相关性 C 是变形参数或是位移及其导数的泛函.使其相关性 C 取最大值的试凑变形即为其真实变形场.这一方法在细观测量中应用得到满意的结果.     

Sequential evaluation of continuous deformation field of semi-crystalline polymers during tensile deformation accompanied by neck propagation

The localized deformation field of high density polyethylene and polypropylene during a tensile test accompanied by neck propagation was quantitatively evaluated based on the network digital image correlation method. In the proposed method, the continuity of the deformation field around a point of interest was introduced for accurate evaluation of the displacement. The accuracy of the proposed method was verified through test images. Using the proposed method, the development of a non-uniform displacement field during tensile tests was evaluated from sequential digital images. The local strain rate was almost uniform until the nominal stress reached its maximum value. After the maximum stress was reached, non-uniform deformation developed at a part of the gauge region of the specimen. A decrease in nominal stress induced a reduction of the local strain rate at regions other than the necked zone. In this study, the cross section average local true stress, strain, and strain rate can be evaluated from the local displacement field. Thus, the relationship between these quantities was evaluated during the tensile tests. Using the proposed method, the local response under wide ranges of strain and strain rate can be evaluated from a few test conditions of tensile strain rate and a small range of tensile strain. Finally, the relationships between gradients of stress, strain, and strain rate under uniaxial tension are discussed. These non-local quantities deviated from those predicted by constitutive equations when the domain size used to evaluate the local quantities was large.     

Explicit and implicit viscoplastic models for polymeric composite

The viscoplastic behavior of a carbon-fiber/polymer matrix composite was investigated through two different modeling efforts. The first model is phenomenological in nature and utilizes the tensile and stress relaxation experiments to predict the creep strain. The phenomenological model was constructed based on the overstress viscoplastic model. In the second model, the composite viscoplastic behavior is captured via neural networks formulation. The neural networks model was constructed directly from the experimental results obtained via creep tests performed at various stress–temperature conditions. The neural network was trained to predict the creep strain based on the stress–temperature–time values. The performance of the neural model is evaluated through the mean squared error between the neural network prediction and the experimental creep strain results. To minimize this error, several optimization techniques were examined. The minimization of the error when carried out by the Truncated Newton method outperforms the standard back-propagation and the conjugate gradient method in terms of convergence rate and accuracy. Using neural network with truncated Newton training algorithm, the prediction of the creep strain was very satisfactory compared to the phenomenological model.     

两点应变测量法在SHPB测量技术上的运用

介绍了两点应变测量法在分离式Hopkinson压杆 (SHPB)测量技术上的运用。该方法通过测量一根压杆两个不同地方的应变 ,利用一个简单的反复过程将压杆中相对传播并叠加在一起的右行波与左行波分离 ,从而利用输入杆对试件的多次加载来研究软材料的动态力学性能。利用该方法计算所得的最大应变比利用传统SHPB测量技术得到的最大应变增大了 2～ 3倍。     

Two-dimensional analysis of progressive delamination in thin film electrodes

By employing the two-dimensional analysis, i.e., plane strain and plane stress, a semi-analytical method is developed to investigate the interfacial delamination in electrodes. The key parameters are obtained from the governing equations, and their effects on the evolution of the delamination are evaluated. The impact of constraint perpendicular to the plane is also investigated by comparing the plane strain and plane stress. It is found that the delamination in the plane strain condition occurs easier, indicating that the constraint is harmful to maintain the structure stability. According to the obtained governing equations, a formula of the dimensionless critical size for delamination is provided, which is a function of the maximum volumetric strain and the Poisson’s ratio of the active layer.     

单轴拉伸过程中双相不锈钢局部微观变形行为的细观力学有限元分析

针对双相不锈钢中奥氏体相和铁素体相分别展开了纳米压痕实验,并通过有限元反演得到两相各自的拉伸应力-应变关系,利用Voronoi Tessellation法生成代表性的微结构体积单元,对双相不锈钢的单轴拉伸行为进行了有限元仿真和模拟,研究了双相不锈钢在拉伸过程中的局部应力、应变分布和演化规律．结果表明,利用Voronoi Tessellation法建立单元模型,结合本文通过纳米压痕实验获取的两相力学性能参数,可以很好地模拟双相不锈钢的整体单拉行为,奥氏体比铁素体软,拉伸载荷下双相不锈钢的应变集中在奥氏体中,应力集中在铁素体中;局部应力应变的分布特征与两相分布特征和晶粒形状有关,最大应变值主要集中在奥氏体晶粒狭长且尖锐的区域,而最大应力则主要发生在铁素体晶粒狭长和尖锐的区域;对于奥氏体和铁素体晶粒占比相当的双相不锈钢,其虽然可以具有较为综合的宏观力学性能,但是其微观应力集中的区域和应力最大值相对较大．研究成果为进一步揭示双相不锈钢局部失效机理奠定了基础．     

The initiation and growth of adiabatic shear bands

A simple version of thermo/viscoplasticity theory is used to model the formation of adiabatic shear bands in high rate deformation of solids. The one dimensional shearing deformation of a finite slab is considered. For the constitutive assumptions made in this paper, homogeneous shearing produces a stress/strain response curve that always has a maximum when strain and rate hardening, plastic heating, and thermal softening are taken into account. Shear bands form if a perturbation is added to the homogeneous fields just before peak stress is obtained with these new fields being used as initial conditions. The resulting initial/boundary value problem is solved by the finite element method for one set of material parameters. The shear band grows slowly at first, then accelerates sharply, until finally the plastic strain rate in the center reaches a maximum, followed by a slow decline. Stress drops rapidly throughout the slab, and the central temperature increases rapidly as the peak in strain rate develops.     

几种非均匀应变有限单元的最大特征频率和稳定的时间步距

通过多点高斯积分研究了非均匀应变有限单元的最大特征频率,给出了单相和两相介质若干简单、非均匀应变有限单元最大特征频率上界的计算公式,扩充了Flanagan的研究结果,由此,给出了几种显式积分格式的实用稳定性条件,并通过两相介质的算例,检验了该稳定性条件。