高强钢筋混凝土柱地震损伤模型研究

为研究配置高强钢筋混凝土柱在地震作用下的损伤情况，对10根高强钢筋混凝土柱开展低周反复荷载试验。基于试验结果，采用修正的Park-Ang损伤模型进行分析。针对不同模型进行高强钢筋混凝土柱的损伤计算，分别对其适用性进行全面评价，建立考虑幅值和累积耗能相互作用的损伤理论模型。研究结果表明：Chai模型、Kunnath模型、傅剑平模型的准确性较好，付国模型和陈林之模型计算得到的结果偏大。本研究模型的计算结果与试验结果较为一致，可用于高强钢筋混凝土柱的损伤计算。     

疲劳／断裂加速试验载荷谱的编制及其实验研究

本文根据损伤等效原理，提出一套供随机疲劳试验用的加速载荷谱编制方法。由于此加速试验谱保持与原始实测谱主波型态和载荷序列不变，只对二级波进行等损伤折算，故经试验证实：加速试验谱对构件造成的损伤与原谱一致，即二者给出的寿命相当。加速试验谱可大大压缩试验时间，其占用的机时只有原谱的１／４左右。     

混凝土与纤维混凝土的劈裂试验及损伤描述

描述工程材料在服役期间所受到的损伤，是评估其可靠度、耐久性等指标的重要依据，本文根据混凝土与纤维混凝土劈裂试验的结果，对一些损伤模型存在的问题进行的探讨认为：对于混凝土复合材料，卸载曲线的斜率受到粗骨料和纤维等因素的干扰，卸载刚度的衰减不能精确描述损伤的演化，并且，针对不同的极限状态，损伤描述应该有不同的形式，针对损伤对混凝土抗渗性能的影响问题，本文提出了损伤描述表达式。     

受压混凝土的不可逆变形与刚度衰减的研究

本文根据内变量定义，引入表征塑性发展和产生损伤的内变量，根据塑性力学和损伤学方法，结合混凝土单调受压应力一应变全曲线的试验结果，对混凝土不可逆变形和刚度衰减进行了研究，经与反复加卸载试验结果相比，吻合较好，如果将其推广至反复加卸载试验极为困难的复杂受力工况将是方便有效的。     

绕丝加固预损钢筋混凝土柱的抗震性能试验研究

对4根钢筋混凝土柱进行了模拟地震的预损伤、预损伤后绕丝加固和加固后的低周往复荷载破坏试验,研究了绕丝加固地震损伤钢筋混凝土柱的抗震性能。根据试验数据分析了试件的承载力、延性性能、刚度退化及耗能能力。试验结果表明:经过绕丝加固修复后的预损伤试件,其延性性能和极限位移得到了明显提高;钢筋混凝土柱的预损伤程度对预损伤后的加固效果有重要影响。在轻度损伤程度情况下,绕丝加固柱恢复并超过受损前的抗震性能;预损伤越大的柱经绕丝加固后其延性、耗能能力、刚度和承载力越小。     

疲劳损伤状态的试验研究

从疲劳过程中材料显微组织结构的变化特征、疲劳损伤的非线性效应等方面进行分析与论证，提出了不存在一般意义上的“等效损伤状态”的观点，采用高－低和低－高两组循环载荷下的损伤累积试验，对传统意义上的“等效损伤状态”下的剩余寿命试验进行了验证。     

修正的RC剪力墙构件Park-Ang损伤模型

基于Park-Ang 损伤模型，提出了用于钢筋混凝土剪力墙构件的修正损伤模型．通过对已有钢筋混凝土剪力墙试验结果的统计分析，总结了其累积耗能组合系数的影响因素，并拟合出该系数与试件参数：剪跨比、轴压比、配筋率的关系式．修正的损伤模型需满足加载至破坏时损伤指标为1.0 的上界条件，结果表明，根据本文修正的损伤模型计算的钢筋混凝土剪力墙试件损伤指标在统计意义上满足该条件．最后，根据构件性能水准的相关研究，本文将钢筋混凝土剪力墙构件的性能水准划分为：基本运行，生命安全和接近倒塌，分别对应了构件骨架曲线相应关键点：屈服点、峰值点和极限破坏点，根据本文修正损伤模型计算的各水准损伤指标临界值分别为：0.02、0.45 和1.00．     

冻土破坏过程的微裂纹损伤区的计算分析

对冻土破坏过程进行了试验研究，冻土破坏的过程是微裂纹损伤与临界串接的演化过程，确认了冻土微裂纹损伤区的存在，并分别用莫尔准则和最大拉应力准则建立了微裂纹损伤区计算模式。将微裂纹损伤区按缺陷处理并简化为当量裂纹，进行了裂纹尺寸的定量计算，结果表明其尺寸与冻土中初始裂纹尺寸相当，将计算结果与观测结果相比较，误差不超过10％。     

利用位移引伸计测定薄板单轴损伤演化曲线的试验方法研究

一套准确而又简便的测试损伤变量的实验方法，对于推动连续介质损伤力学的工程应用是至关重要的。本文系统研究了利用位移引伸计测定薄板材料单轴损伤演化曲线的试验方法。采用引伸计测量大圆弧变截面试样中心部位某一标距段的伸长量，然后计算得到弹性模量的变化，进而确定损伤变量。文中就试样形状尺寸的确定、主损伤区弹塑性大应变的测控和卸载弹性模量的稳定性、与精确测量等关键测试技术问题进行了深入细致的分析和实验研究，并从多角度对该试验方法的正确性进行了实验验证。文中还介绍了该试验方法在确定LY12-CZ铝合金薄板单轴损伤演化曲线的应用，实验表明本文建议的试验方法是简便有效的，初步奠定了发展标准化损伤曲线测试方法的基础。     

基于电能耗散的金属材料疲劳损伤测量

根据电磁学原理，提出了基于电能耗散的疲劳损伤定义，指出其较能反映金属材料疲劳损伤的特征。获得了用电阻变化测量疲劳损伤的公式，应用计及疲劳极限和循环应力幅影响的非线性累积疲劳损伤模型，给出了金属材料疲劳损伤的剩余寿命预测公式。通过正火45^#碳钢的旋转弯曲疲劳试验，验证了本文提出的剩余寿命预测公式的可靠性，和韧性耗散测量疲劳损伤相比较；说明了用电阻测量疲劳损伤的合理性。     

疲劳损伤临界值分析

通过对疲劳过程和疲劳失效的临界状态的分析，提出疲劳失效判据应与损伤程度和应力水平两个因素有关，并在试验的基础上建立了一个剩余强度退化的对数模型。根据疲劳过程中材料强度退化的事实及其规律。分析了损伤临界值与循环应力水平之间的关系，给出了一般应力水平下疲劳损伤临界值的范围，对于随机疲劳问题，给出了损伤临界值的分布规律。     

A micromechanical study of residual stress and its effect on transverse failure in polymer–matrix composites

Cure residual stress and its effect on damage in unidirectional fibre-reinforced polymer–matrix composites under transverse loading were studied using a micromechanical unit cell model and the finite element method. The overall residual stress introduced from curing was determined by considering two contributions: volume shrinkage of matrix resin from the crosslink polymerization during isothermal curing and thermal contraction of both resin and fibre as a result of cooling from the curing temperature to room temperature. To examine the effect of residual stress on failure, a model based on the Maximum Principal Stress criterion and stiffness degradation technique was used for damage analysis of the unit cell subjected to mechanical loading after curing. Predicted damage initiation and evolution are clearly influenced by the inclusion of residual stress. Residual stress is always detrimental for transverse compressive loading and pure shear loading. For transverse tensile loading, residual stress is detrimental for relatively low resin strength and beneficial for relatively high resin strength. Failure envelopes were obtained for both biaxial normal loading and combined shear and normal loading and the results show that residual stress results in a shifting and contraction of the failure envelopes.     

Understanding delamination behaviour in a circular laminate

Composite materials are prone to a wide range of defects and damage which may significantly reduce their residual strength. Of the various types of defects possible, interply delaminations arising from in-service damage are probably the most insiduous because of their effects on residual compressive strength and difficulties associated with their detection. In this study, a finite element analysis of the self similar growth of a circular delamination in a compressed laminate is undertaken, and the results are compared with an analytical solution.     

Designing for tolerance to impact damage at fastener holes in graphite/epoxy laminates under compression

This paper illustrates how fracture mechanics tools may be used to estimate the residual strength of impact damaged fastener holes in composite laminates. Finite element analysis is carried out in order to study the effect of the delamination damage. It is shown that as the size of the damage is increased, a stage is reached after which a significant further increase in damage does not result in a significant decrease in residual compressive strength.     

A DAMAGE CONSTITUTIVE MODEL OF ROCK WITH CONSIDERATION OF RESIDUAL STRENGTH

基于岩石微元强度服从Weibull分布规律,引入损伤变量修正因子,建立了考虑残余强度影响的岩石损伤本构模型.运用多元函数求极值的方法,推导了含修正系数的模型参数\(m\)和\(F_{0}\)的理论表达式;对模型修正因子的选取进行了讨论分析. 结果表明：本文修正模型的实质是增加了一个含有修正系数的线性项;修正系数 \(\delta \)主要反映岩石的残余强度特征,选取合适的 \(\delta \) 值可以提高修正后本构模型的准确性.     

复合材料层合板的低速冲击损伤及其剩余压缩强度研究

本文采用理论和实验方法研究了复合材料层合板的低速冲地及其剩余压缩强度。文中利用有限元方法和能量转换原理计算了层合板受到低速冲击的受载最危险状态，以及此时的应力分布；并用Ｔｓａｉ－Ｗｕ张量准则判断损伤情况，对产生损伤的单元进行相应的刚度折减，且作重复计算直至不产生新的损伤为止；最后，对受冲击的层合板还进行剩余压缩强度计算。在实验中，采用激光全息无损检测法测量了层合板的冲击损伤，并对受冲击的层合板进行     

Fatigue damage of APC-2 composite assessed from material degradation and non-destructive evaluation data

Quasi-isotropic 45° APC-2 specimens are fatigued under constant amplitude stress reversal load condition. Fatigue induced degradation of the mechanical properties is correlated to data obtained from non-destructive evaluation. C-scan readings were used to define a generic damage severity factor D. It refers to the current fatigue damage state and accounts for the varying severity of damage at the different specimen locations. Analytical expressions are developed to relate D to the axial stiffness, residual strength and interlaminar shear strength. An indication of damage tolerance can thus be made for evaluating the integrity of structural components.     

Vibration based damage detection in a uniform strength beam using genetic algorithm

Cantilever steel beams of uniform strength are having various industrial applications. In particular when it is used as leaf spring it undergoes very large deflection in comparison to beam of uniform cross section. The damage occurs in these beams mainly due to fatigue loading. Early detection of damage in such type of beams is very essential to avoid a major failure or accident. In this paper, firstly formulation of an objective function for the genetic search optimization procedure along with the residual force method are presented for the identification of macroscopic structural damage in an uniform strength beam. Two cases have been investigated here. In the first case the width is varied keeping the strength of beam uniform throughout and in the second case both width and depth are varied to represent a special case of uniform strength beam. The developed model require experimentally determined data as input and detect the location and extent of the damage in the beam. Here, experimental data are simulated numerically by using finite element models of structures with inclusion of random noise on the vibration characteristics. It has been shown that the damage may be identified for the said problems with a good accuracy.     

金属材料的非线性疲劳累积损伤模型及强度衰减分析

用连续介质损伤力学的方法推导得到了一个非线性的损伤发展方程，该方程计及了加载过程应力与损伤的完全耦合效应；又由损伤发展方程得到了一个计及加载循环周内和循环周间损伤积累非线性效应的完全非线性疲劳累积损伤模型，已有的部分非线性疲劳累积损伤模型成为它的特例。由损伤发展方程确定了材料剩余强度随损伤发展的衰减规律和临界损伤值。     

极端环境下连续碳纤维增韧的陶瓷基复合材料的力学行为

连续纤维增韧的碳化硅复合材料(以下简称C/SiC),作为超高速飞行器热结构使用时,有可能在高温环境下受到高速撞击的作用,因此,掌握其在极端环境(高温、高应变率)下的力学性能是进行结构安全设计的基础。本文采用具有高温实验能力的分离式Hopkinson杆,在293~1273K温度范围内进行了动态压缩力学性能测试,研究了环境温度和加载速率对材料力学性能的影响。结果表明:C/SiC复合材料的高温压缩力学性能主要受应力氧化损伤和残余应力的共同影响。实验温度低于873K时,应力氧化损伤的影响很小,而由于增强纤维和基体界面残余应力的释放使界面结合强度增大,复合材料的压缩强度随温度的升高而增大;当实验温度高于873K时,应力氧化损伤加剧,其对压缩强度的削弱超过残余应力释放对强度的贡献,材料的压缩强度随温度的升高逐渐降低。由于应力氧化损伤受应变率的影响很大,当温度由873K升高至1273K时,高应变率下压缩强度降低的程度要比应变率为0.0001/s时低得多。