弹脆性材料的损伤本构关系及应用

本文根据连续损伤力学方法,对弹脆性材料损伤的力学响应进行一般分析。理论分析中,材料与损伤都是各向异性的。还导出了计算损伤张量、有效弹性张量、真实应力张量以及损伤能耗率张量的实用表达式。     

局部损伤复合材料层合板的振动分析

本文采用了一种改进方法对局部损伤复合材料层合板进行了振动分析,将复合材料板中的损伤模拟为局部刚度的削减,并取三个损伤因子来刻画损伤的特性．利用高阶摄动法对其自由振动方程进行求解,主要计算了损伤板的自然振动频率和振动模态．相较于一阶摄动展开法,该方法在计算局部较大损伤问题中具有更高的准确度和敏感度．最后对损伤问题进行了参数研究,分析了不同的损伤因子（包括局部损伤程度、方向、面积大小）对板自由振动频率的影响．该方法为二维板局部损伤检测提供了有效精确的理论依据,并为损伤的定量评价提供了一种思路．     

增量型各向异性损伤理论与数值分析

考虑到目前各向异性损伤理论存在一些不足,该文在增量型各向异性损伤理论的框架下,引入二阶对称张量,构造四阶对称有效损伤张量,建立了有效应力方程．类似于塑性流动分析方法,定义了增量弹性应力．应变关系．利用von Mises塑性屈服准则,并考虑各向异性损伤效应,推导出四阶对称的弹．塑性变形损伤刚度张量,其对称性反映了材料的固有特性．根据物体的变形和现时损伤状态,构造了材料损伤演化方程,方程中各项具有明确的物理意义．通过对A12024-T3金属薄板单向拉伸的有限元分析,确定了损伤演化参数,验证了损伤演化方程的正确性．此外还对含孔口薄板做有限元模拟,讨论了反力—位移曲线的变化规律以及它所揭示变形性质,给出了损伤场的分布规律。     

基于修正Park-Ang模型的圆钢管构件地震损伤评估

为合理评估薄壁圆钢管构件的地震损伤程度,基于Park-Ang地震损伤模型,通过修正相关参数,建立了适用于圆钢管构件的地震损伤模型。利用圆钢管构件在低周反复荷载作用下的骨架曲线,给出了损伤模型中各待定参数的计算方法,在此基础上通过反演构件破坏点损伤因子为1.0时的模型组合系数,并利用曲线拟合法得到模型组合系数与构件轴压比、长细比和径厚比等参数间的关系式,从而建立构件的地震损伤评估模型。结果表明,修正的Park-Ang损伤模型可较好地评估圆钢管构件的损伤程度,构件达到极限破坏时的损伤因子值收敛于1.0且离散性较小,构件的破坏程度可划分为基本完好、轻微与中等破坏、严重破坏和失效破坏,对应的损伤因子界限值分别为0.02,0.41和1.00。     

空中爆炸冲击波对生物目标的超压-冲量准则

针对空中爆炸冲击波对生物目标的毁伤准则问题,超压-冲量毁伤准则可弥补单一毁伤准则的缺陷。首先,根据空中爆炸冲击波特征参量的一般形式,提出一种归一化毁伤准则形式,给出基于毁伤律的毁伤准则与判据的获取方法。其次,在不同爆炸条件对生物目标进行毁伤效应实验,依据生物整体的损伤情况确定出毁伤等级,对应获得的离散的实验数据确定连续性的超压-冲量曲线,继而拟合出不同毁伤等级的超压-冲量准则的表达式,所得到的超压-冲量准则可以评估生物目标的毁伤问题。     

混凝土分段曲线损伤模型

在对比分析国内外现有的混凝土受拉损伤模型基础上，结合素混凝土受拉应力应变曲线的试验结果，提出了一个新的混凝土分段曲线损伤模型，并利用应力连续条件确定了损伤模型中各系数的值。运用该模型到力学分析中，推导了矩形截面的混凝土梁在纯弯矩作用下，在损伤较小和损伤较大时的力学方程，算出了梁的最大承载能力，并与材料力学计算的梁承载能力进行了对比。详细分析了损伤区域及损伤应力在横截面上的变化过程，确定了极限状态下含损伤混凝土梁的应力分布和相应的承载能力，画出了损伤状态梁截面的应力分布图。     

基于支持向量机的结构损伤分步识别研究

支持向量机是一种基于统计学习理论的机器学习算法,能够较好地解决小样本的学习问题。本文介绍了支持向量机分类和回归算法,提出了基于支持向量机的结构损伤分步识别方法:以模态频率作为损伤特征,首先根据支持向量机分类算法的概率估计确定可能的损伤位置,重新构造训练样本,然后利用支持向量机回归算法计算损伤位置;最后估计损伤程度。以梁的损伤识别为例进行了验证,结果表明该方法可以提高损伤识别的精度。     

The near tip fields and temperature distribution around a crack in a body of hardening material containing small damage

In this paper, the following conclusions are reached: The influence of damage on the stress and strain feilds can be neglected in an asymptotic sense for the solutions of damage field in a plastic solid containing small damage. The formulation of the problem is simplified with an uncoupled approach. Based on experimental results of plastic damage, most of the damage in the material are considered as small damage with the critacal damage variable ω _c ≪1. Using this approach, closed form expressions of the near tip damage fields for mode III, mode I and the temperature distribution induced by plastic dissipation in a hardening material containing damage are deduced. We point out that the temperature distribution in the process zone is strongly dependent on the damage of materials even for the small damage case. The results of the predicted value of the temperature rise near the tip region ignoring the damage effect is appreciably higher than the observed data. The main reason of this discrepancy is the presence of damage dissipation and the fact that its influence on the calculation of plastic dissipation have not been appropriately taken account of. The calculation is improved by taking into account the damage effect on the temperature rise, then theT _max value is in better accord with the experimental value. The project supported by the National Natural Science Foundation of China.     

General Expressions of Constitutive Equations for Isotropic Elastic Damaged Materials

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考虑温度效应的弹性损伤一般理论

现有的各种损伤理论基本上都是关于等温问题的 ,且在不同程度上依赖于某些经验假设。本文在严格的不可逆热力学理论基础之上 ,建立了考虑温度效应的弹性损伤一般理论。推导出热弹性各向同性与各向异性损伤材料全部本构方程的一般形式 ,其中包括应力 应变关系、熵密度方程、损伤对偶张量表达式、热 固 损伤耦合的热传导方程和损伤演化方程。它们的特殊形式包含了等温各向同性与各向异性弹性损伤的本构方程     

基于构型力内变量的界面损伤问题研究

本文基于材料构型力的基本理论和损伤力学中含有内变量的热力学框架,提出了新的损伤变量定义方式,为研究界面损伤问题提供了一种新思路。首先,基于双相弹性体的能量分析,给出界面材料构型力表达式,通过构型力的离散化方法,实现了其在有限元中的数值计算。其次,定义构型力为界面损伤内变量,进而提出一种新的损伤演化模型,并采用刚度劣化的方法,对该界面损伤模型进行数值实现。最后,通过对复合材料界面损伤问题（有裂纹或无裂纹）进行数值模拟,分析了其界面损伤发展趋势,探讨了此模型的合理性和优越性。基于构型力内变量的界面损伤模型,可为研究复合材料的界面损伤失效问题提供一种普适性的方法。     

Investigation of the damage variable basic issues in continuum damage and healing mechanics

Consistent mathematics and mechanics are used here to properly interpret the damage variable within the confines of the concept of reduced area due to damage. In this work basic issues are investigated for the damage variable in conjunction with continuum damage and healing mechanics. First, the issue of the additive decomposition of the damage variable into damage due to voids and damage due to cracks in continuum damage mechanics is discussed. The accurate decomposition is shown to be non-additive and involves a term due to the interaction of cracks and voids. It is shown also that the additive decomposition can only be used for the special case of small damage. Furthermore, a new decomposition is derived for the evolution of the damage variable. The second issue to be discussed is the new concept of independent and dependent damage processes. For this purpose, exact expressions for the two types of damage processes are presented. The third issue addressed is the concept of healing processes occurring in series and in parallel. In this regard, systematically and consistently, the equations of healing processes occurring either consecutively or simultaneously are discussed. This is followed by introducing the new concept of small healing in damaged materials. Simplified equations that apply when healing effects are small are shown. Finally, some interesting and special damage processes using a systematic and original formulation are presented.     

Bi-variable damage model for fatigue life prediction of metal components

Based on the theory of continuum damage mechanics,a bi-variable damage mechanics model is developed,which,according to thermodynamics,is accessible to derivation of damage driving force,damage evolution equation and damage evolution criteria. Furthermore,damage evolution equations of time rate are established by the generalized Drucker’s postulate. The damage evolution equation of cycle rate is obtained by integrating the time damage evolution equations,and the fatigue life prediction method for smooth specimens under repeated loading with constant strain amplitude is constructed. Likewise,for notched specimens under the repeated loading with constant strain amplitude,the fatigue life prediction method is obtained on the ground of the theory of conservative integral in damage mechanics. Thus,the material parameters in the damage evolution equation can be obtained by reference to the fatigue test results of standard specimens with stress concentration factor equal to 1,2 and 3.     

含热冲击预损伤的陶瓷基复合材料损伤本构模型

陶瓷基复合材料结构在服役过程中不可避免地经受热冲击(较高的热应力梯度)而产生热机械损伤, 因此, 建立含循环热冲击预损伤材料的损伤本构模型, 以描述材料在热机械载荷作用下的力学行为, 对材料结构损伤容限设计与结构完整性评估非常重要. 本文首先对经历了循环热冲击的材料进行单调拉伸损伤实验, 发现对于含循环热冲击预损伤的材料, 其弹性模量的下降与所施加的应变直接相关. 然后在连续介质损伤力学的框架下, 基于平面应力假设, 建立了含循环热冲击预损伤材料的损伤演化模型, 该模型所涉及的参数可通过一个偏轴(45$^\circ$)以及两个正轴(平行于两个主方向)的单调拉伸试验获得. 最后, 采用经典塑性理论对由基体损伤引起的非弹性应变进行了描述. 本文所提出的应变损伤宏观模型可以描述陶瓷基复合材料在热机械载荷作用下的损伤演化, 同时弥补了含预损伤的陶瓷基复合材料在机械载荷下损伤本构模型在理论及实验研究方面的不足.      

A DAMAGE MECHANICS MODEL FOR FATIGUE LIFE PREDICTION OF FIBER REINFORCED POLYMER COMPOSITE LAMINA

A damage mechanics fatigue life prediction model for the fiber reinforced polymer lamina is established. The stiffness matrix of the lamina is derived by elastic constants of fiber and matrix. Two independent damage degrees of fiber and matrix are introduced to establish constitutive relations with damage. The damage driving forces and damage evolution equations for fiber and matrix are derived respectively. Fatigue tests on 0°and 90°unidirectional laminates are conducted respectively to identify parameters in damage evolution equations of fiber and matrix. The failure criterion of the lamina is presented. Finally, the life prediction model for lamina is proposed.     

基于均布荷载挠度曲率的梁结构损伤识别方法

为运用荷载挠度曲线进行损伤识别,通过力法推导了梁结构在均布荷载作用下的挠度曲率理论公式,提出通过损伤前后的挠度曲率差进行损伤定位,针对多跨连续梁均布荷载下挠度曲率指标存在的损伤识别漏判问题,提出逐跨均布荷载挠度曲率指标以避免其影响,并建立了挠度曲率与损伤程度的理论关系式,可对损伤程度进行较精确的定量描述．通过一简支梁和一三跨连续梁算例,考虑多种损伤工况,分析了指标在不同程度噪声水平下的抗干扰能力,验证了挠度曲率损伤指标应用于实际的可行性．     

复合材料层合板面内渐进损伤分析的CDM模型简

基于连续介质损伤力学,提出了一个预测复合材料层合板面内渐进损伤分析的模型,它包括损伤表征、损伤判定和损伤演化3 部分. 模型能够区分纤维拉伸断裂、纤维压缩断裂、纤维间拉伸损伤和纤维间压缩损伤4 种损伤模式,定义了与4 个损伤模式对应的损伤状态变量,导出了材料主轴系下损伤前后材料本构之间的关系. 损伤起始采用Puck 准则判定,损伤演化由特征长度内应变能释放密度控制. 假定材料服从线性应变软化行为,建立了损伤状态变量关于断裂面上等效应变的渐进损伤演化法则. 模型涵盖了复合材料面内损伤起始、演化直至最终失效的全过程. 完成了含孔[45/0/-45/90]_2S 层合板在拉伸和压缩载荷下失效分析,结果表明该模型能合理进行层合板的强度预测和损伤失效分析.     

结构健康监测中的损伤检测技术研究进展

对结构健康监测研究中的结构损伤检测方法及其特点进行了介绍.从基于结构模态分析的方法和基于结构动态试验信号处理的方法两方面,阐述了结构健康监测中的损伤检测方法及其最新研究进展.基于结构模态分析的结构损伤检测方法是针对整个结构的检测,使用的模态都限于低阶模态范围内,所检测的结构应容易建立有限元模型,便于进行响应预测.基于结构动态试验信号处理的损伤检测方法通常是针对结构局部构件的损伤检测,不需要对结构进行有限元建模,而直接从测试的动态响应信号中提取表征结构损伤的特征参数.文中提出了对比性损伤检测方法和非对比性损伤检测方法的概念,并对结构损伤检测中常用的信息传感与处理技术进行了论述,指出了结构损伤检测研究中应该考虑的传感器布置问题.提出了将损伤信息的主动检测与被动检测相结合进行损伤程度判断和剩余寿命估计等问题是有待进一步深入研究的课题.      

疲劳损伤问题中有效应力的一种定义

有效应力是损伤力学中的一个重要概念,这个概念的提出为用无损状态下的本构方程描述有损伤材料的行为提供了有效手段.本文探讨损伤力学中有效应力的定义,通过对损伤演化规律的分析,指出有效应力的一般定义不适用于疲劳损伤问题.本文认为,疲劳问题中的有效应力应该以等效寿命为基础,并根据剩余寿命的概念引入了疲劳损伤问题中有效应力的一种定义.     

On the description of anisotropic damage in composite laminates

A general anisotropic damage theory of cracked laminates is formulated here. The deformation of composite laminates is composed of matrix elastic strains, pseudo-elastic damage strains due to cracking and permanent damage strains due to interlaminar slip. The surface of damage initiation is constructed according to the concept of linear elastic fracture mechanics for the virgin material. After the initial damage, a pesudo-elastic damage can be used to describe the damage behaviour if interlaminar slip is negligible. Damage evolution, load induced anisotropy and interlaminar intralaminar interaction for composite laminates are examined; the latter can perturb the normality structure of damage strain rate. Explicit expressions are given for pseudo-elastic (or secant) moduli of the damaging composite laminates, under a non-interacting assumption imposed on the cracks between different families.