平纹编织SiC/SiC复合材料多尺度建模及强度预测

连续SiC纤维增强SiC基体复合材料（SiC/SiC）具有优异的高温力学性能、辐照稳定性及较低的氚渗透率,在核工程结构领域具有良好的应用前景,掌握其承载状态下的损伤演化和强度性能,对SiC/SiC复合材料的应用具有重要指导意义。本文基于平纹编织SiC/SiC复合材料的制备过程和组分材料分布的多尺度特性,考虑复合材料微观结构的局部近似周期性,建立了纤维丝尺度和纤维束尺度单胞模型。使用有限元分析软件对纤维丝尺度模型的弹性性能和强度性能进行预测,将这些性能参数代入纤维束尺度模型,引入Tsai-Wu失效准则,根据材料的不同失效模式并对失效单元进行方向性刚度折减,模拟了平纹编织SiC/SiC复合材料在单轴拉伸载荷下的渐进损伤过程。数值模拟曲线与试验曲线吻合较好,实现了对平纹编织SiC/SiC复合材料强度的有效预测。      

2.5维C/SiC复合材料经向拉伸性能

将微观尺度的强度预测模型与单胞尺度有限元模型相结合, 建立了2.5维C/SiC复合材料的双尺度强度预测模型。该模型首先计算微观尺度的应力-应变曲线以及最终失效时的力学性能, 然后将其带入单胞模型, 对不同边界条件下单胞模型的弹性模量进行折减, 统计单胞模型的平均应力与应变, 最后得到单胞尺度的应力-应变关系和最终失效时的力学性能。通过2.5维C/SiC复合材料常温和高温条件下的经向单轴拉伸试验, 得到了2.5维C/SiC复合材料经向拉伸过程的应力-应变曲线以及最终失效时的力学性能。结果表明, 理论分析结果与实验值基本一致, 验证了该方法的有效性。     

多尺度模拟SiC/IMI834复合材料失效

基于格林函数和有限元分析的多尺度方法模拟SiC/IMI834复合材料拉伸试验,研究复合材料微区应力分布、宏观力学性能和纤维失效情况。其中有限元分析用来计算SiC/IMI834复合材料微区应力分布并为格林函数提供应力传递集中因子。格林函数用来模拟SiC/IMI834复合材料宏观失效过程及力学性能。结果表明,失效纤维上应力恢复区长度受材料性能影响,与外加载荷无关;距离失效纤维越远,沿失效端面纤维上轴向应力越低;距离失效纤维越近,沿失效端面基体上轴向应力越低;SiC/IMI834复合材料宏观失效应变随纤维体积分数增加而提高,但SiC/IMI834复合材料初始纤维失效与纤维体积分数无关,拉伸应变均为0.01。     

针刺C/SiC复合材料应力-应变模型及试验验证

研究了室温下针刺C/SiC复合材料的静拉伸应力-应变行为。基于显微CT技术重构的微观型貌,选取恰当的代表体积单元,建立了针刺C/SiC复合材料应力-应变性能预测的单胞模型。基于可实现任意加卸载下单向纤维增强C/SiC复合材料应力-应变计算的界面摩擦模型,由材料的细观组分性能计算出单向纤维束层的应力-应变响应,然后将单向纤维束层的应力-应变响应代入到单胞模型中,通过有限元法计算得到针刺C/SiC复合材料的整体应力-应变响应。进行了针刺C/SiC复合材料静拉伸试验,测得材料的应力-应变响应,计算结果与试验吻合较好。      

二维编织陶瓷基复合材料偏轴拉伸力学性能预测

基于二维编织C/SiC复合材料的细观结构,建立了碳纤维丝/热解碳界面/SiC基体和纤维束/表层SiC基体两种尺度下的细观单胞模型,通过有限元方法计算碳纤维丝/热解碳界面/SiC基体模型的等效弹性常数和强度,然后代入纤维束/表层SiC基体模型中计算,并引入Tsai-Wu失效准则,考虑不同失效模式的损伤,建立了二维编织C/SiC复合材料的渐进损伤模型,模拟了其偏轴拉伸应力-应变行为。针对该模型,阐述了二维编织C/SiC复合材料单胞模型在复杂应力状态下其纤维束的损伤过程。数值模拟结果与实验数据吻合较好,验证了模型的有效性,为该种材料的力学性能分析提供了一种有效方法。     

基于单胞解析模型的复合材料层合板渐进损伤数值分析

基于单胞解析模型,建立一种从复合材料细观组分到宏观层合板的渐进损伤分析模型。根据连续介质力学和均匀化方法构建细-宏观关联矩阵,通过该矩阵将细观组分材料的弹性和损伤性能传递到宏观复合材料中。该模型只需给出纤维和基体的材料属性及纤维体积含量无需层合板的弹性和强度参数,通过组分材料的损伤失效判据确定其是否损伤,如果发生损伤则用损伤因子折算成相应的刚度衰减。通过用户材料子程序UMAT 及VUMAT将单胞解析模型以及损伤理论嵌入到有限元软件ABAQUS 中,对开孔复合材料层合板的渐进损伤过程进行模拟,预测了层合板强度。结果表明:预报的强度与试验值吻合较好,验证了该方法的有效性。     

三维编织SiC/SiC复合材料拉伸和弯曲损伤机制

为了研究三维编织SiC/SiC复合材料损伤机制,开展了室温条件下的单调拉伸和三点弯曲试验。实验前,利用CT扫描手段,明确了三维编织SiC/SiC复合材料试样的编织组织形态。对拉伸和三点弯曲试样的微观分析表明:原生孔洞和微裂纹导致了材料在单调拉伸过程中形成局部应力集中,随着拉伸载荷的增大,基体的横向开裂和纤维束间纵向层间裂纹逐渐演化形成纤维内部裂纹,导致材料最终的脆性断裂失效;在三点弯载荷作用下,表现为剪切、拉压共生的多耦合破坏模式,拉应力一侧首先发生失效,随后在中性面处发生剪切破坏,紧接着失效迅速向上下两侧扩展,直至截面在整个厚度方向发生失效;断口与纤维束的走向相关性很大,裂纹基本上沿着纤维束之间的界面进行扩展,导致最终失效未发生在理论失效位置处。      

土木结构损伤多尺度并发计算方法及其应用

大型土木结构的损伤破坏是跨尺度演化的结果, 因此单一尺度下的结构分析难以正确地反映结构的非线性损伤失效过程。该文根据结构损伤在宏观、细观尺度下的不同特征建立结构一致多尺度模型, 并通过多点约束法进行跨尺度关联, 实现了结构整体线弹性响应分析和局部细节易损部位的细观层次上弹塑性损伤分析的并发进行。计算结果表明:该文提出的结构损伤多尺度并发计算方法能够兼顾结构整体上的线弹性响应和局部易损部位在细观层次上的塑性损伤特征, 在对结构多尺度响应与损伤特征进行准确描述的基础上, 能够获得结构易损局部的细观损伤状态、演化过程及其对结构宏观响应与失效的影响。     

SiC/Al双连通复合装甲材料抗侵彻性能宏–微观跨尺度模拟

SiC/Al双连通复合装甲材料所具有的复杂三维微结构特征对其宏观抗侵彻性能具有重要影响。本文建立了从宏观靶试模型中SiC/Al靶板的典型微区提取动态边界条件,并作用于相应微观组织模型的跨尺度数值模拟方法,研究了SiC/Al靶板在抗侵彻过程中不同典型局部微区内的动态微结构损伤及失效过程。研究表明:在弹着点正下方位置,多个裂纹源萌生于两相界面处靠近陶瓷相一侧,随后沿与弹道平行的方向扩展并形成轴向主裂纹;在与弹体轴线呈45°位置,裂纹除了在靠近界面处的陶瓷相一侧萌生外,在陶瓷相内部也出现了与弹道方向垂直的多条水平裂纹,界面裂纹与水平裂纹进一步扩展并桥连成多个锥形主裂纹。相关模拟方法为将来该类材料的微结构优化提供了一种新的技术途径。     

基于改进遗传算法的C/SiC拉伸损伤声发射模式识别

采用层次聚类及基于改进遗传算法的无监督模式识别方法,对2D-C/SiC复合材料常温拉伸试验过程的声发射数据进行分析,结合试样断口的扫描电镜(SEM)照片,得到拉伸过程中5类损伤模式及其典型声发射特征参数。通过对各类损伤的能量分布、累计事件数和累计能量的分析,研究C/SiC复合材料的损伤演化过程,发现其过程可分为基体微裂纹和界面失效为主的初始损伤阶段、基体微裂纹停滞导致层间剥离及纤维失效占主导地位的裂纹饱和阶段、基体长裂纹和界面失效为主的损伤积累发展阶段和纤维束大量失效的宏观断裂阶段。     

Damage advancement behavior in braided composite structures for mini aerial vehicles

This work provides a systematic approach to accurately predict damage progression in a composite structure subjected to bending load. Landing gear structures for unmanned aerial vehicles were fabricated from braided textile preforms and assessed for flexural behavior. A multiscale finite element analysis model was developed for analyzing the progressive damage of these structures under bending loads. Microscale and mesoscale analyses were carried out first. Subsequently, the results of microscale and mesoscale analyses were used as inputs in macroscale analyses that predicted the progressive damages in the entire landing gear structure. The numerical results were validated by experimental studies.     

A Modeling Approach Across Length Scales for Progressive Failure Analysis of Woven Composites

This paper presents a multiscale modeling approach for the progressive failure analysis of carbon-fiber-reinforced woven composite materials. Hierarchical models of woven composites at three different length scales (micro, meso, and macro) were developed according to their unique geometrical and material characteristics. A novel strategy of two-way information transfer is developed for the multiscale analysis of woven composites. In this strategy, the macroscopic effective material properties are obtained from property homogenizations at micro and meso scales and the stresses at three length scales are computed with stress amplification method from macroscale to microscale. By means of the two-way information transfer, the micro, meso and macro structural characterizations of composites are carried out so that the micromechanisms of damage and their interactions are successfully investigated in a single macro model. In addition, both the nucleation and growth of damages are tracked during the progressive failure analysis. A continuum damage mechanics (CDM) method is used for post-failure modeling. The material stiffness, tensile strength and damage patterns of an open-hole woven composite laminate are predicted with the proposed multiscale method. The predictions are in good agreement with the experimental results.     

Multiscale finite element modeling of failure process of composite laminates

A multiscale nonlinear finite element modeling technique is developed in this paper to predict the progressive failure process for composite laminates. A micromechanical elastic–plastic bridging constitutive model, which considers the nonlinear material properties of the constituent fiber and matrix materials and their interaction and the damage and failure in fibrous composites at the fiber and matrix level, is proposed to represent the material behavior of fiber-reinforced composite laminates. The micromechanics constitutive model is employed in the macroscale finite element analysis of structural behavior especially progressive failure process of the fiber-reinforced composites based on a 4-node 24-DOF shear-locking free rectangular composite plate element.     

Physics‐based multiscale damage criterion for fatigue crack prediction in aluminium alloy

In this paper, a physics‐based multiscale approach is introduced to predict the fatigue life of crystalline metallic materials. An energy‐based and slip‐based damage criterion is developed to model two important stages of fatigue crack initiation: the nucleation and the coalescence of microcracks. At the microscale, a damage index is developed on the basis of plastic strain energy to represent the growing rate of a nucleated microcrack. A statistical volume element model with high computational efficiency is developed at the mesoscale to represent the microstructure of the material. Also, the formation of a major crack is captured by a coalescence criterion at mesoscale. At the macroscale, a finite element analysis of selected test articles including lug joint and cruciform is conducted with the statistical volume element model bridging two scale meshes. A comparison between experimental and simulation results shows that the multiscale damage criterion is capable of capturing crack initiation and predicting fatigue life.     

Fatigue Hysteresis Behavior of 2.5D Woven C/SiC Composites: Theory and Experiments

This paper presents an intriguing fatigue hysteresis behavior of 2.5 dimensional woven C/SiC composites via the integration tool of advanced experimental techniques with a multiscale theoretical model. Tension-tension fatigue experiment has been carried out to predict the fatigue hysteresis properties of 2.5D woven C/SiC composite at room temperature, accompanied with the fracture of specimens to investigate the mechanism of fatigue damage. Meanwhile, a multiscale fatigue model of 2.5D woven C/SiC composites, which encompasses a micro-scale model of fiber/matrix/porosity in fiber tows and a macro-scale model of unit-cell, has been proposed to provide a reliable validation of the experimental results based on fiber damages resulting from relative slip motion with respect to matrix at interfaces and the architecture of 2.5D woven C/SiC composites. The predicted hysteresis loop from theoretical model at room temperature holds great agreement with that from tension-tension fatigue experiments. Also, effects of fatigue load, braided structural parameters and material properties at micro scale on fatigue hysteresis behavior have been investigated.     

三维编织复合材料渐进损伤模拟及强度预测

采用考虑纤维束相互挤压的纤维束截面八边形单胞模型, 引入周期性边界条件, 对三维编织复合材料的渐进损伤过程进行数值模拟, 并预测了材料的拉伸强度。通过在应变能密度函数中引入损伤状态变量, 建立了含损伤材料的刚度矩阵, 运用基于不同失效模式下损伤状态变量的刚度渐进折减法表征材料积分点损伤, 通过数值结果与试验结果的对比, 分析了Hashin和Tsai-Wu两种准则作为判定纤维束起始损伤的适用性。分析表明: 基于引入不同失效模式的Tsai-Wu准则的数值模拟和试验结果吻合良好; Hashin准则不适合作为编织纤维束的损伤判据; 不同编织角材料的失效机制不同。      

含界面相三维全五向编织复合材料拉伸行为模拟及失效机制研究

基于三维全五向（Q5D）编织复合材料的细观结构模型,通过引入界面相单元,建立了含界面相Q5D编织复合材料单轴拉伸损伤失效分析模型。应用Python语言实现对ABAQUS的二次开发,将Linde等提出的失效准则和Von-Mises应力准则分别用于纱线和基体的渐进损伤判断,并确定材料的整体失效模式;对于界面相,采用Quads准则进行损伤判断。利用周期性位移边界条件,对含界面相Q5D编织复合材料的纵向拉伸应力-应变行为进行了渐进损伤数值模拟,详细讨论了在纵向拉伸载荷作用下材料的细观损伤起始、扩展和最终失效的演化过程,分析了材料的细观损伤失效机制,预测了材料的极限破坏强度,并研究了界面相性能对材料整体力学行为的影响规律。研究结果表明,数值模拟结果与实验值吻合较好,验证了渐进损伤模型的有效性,为该类材料的力学分析和优化设计奠定了基础。     

基于面-内胞模型的三维四向编织复合材料渐进损伤数值模拟

为了准确预测三维四向编织复合材料的纵向拉伸力学性能,对编织复合材料的面胞和内胞细观实体模型进行参数化建模,面胞模型考虑了纱线空间轨迹的偏移和横截面的挤压变形。用体素网格离散模型并施加合适的边界条件,将各组分材料的损伤模型编入到有限元分析软件ABAQUS用户定义材料子程序UMAT中。分别对内编织角为30°和45°的三维四向碳纤维/环氧树脂编织复合材料的面-内胞模型进行数值分析,经体积加权平均获得不同厚度编织复合材料试件的纵向拉伸模量和强度,通过统计具有相同破坏模式的积分点数量研究复合材料的渐进损伤过程。结果表明:基于面-内胞模型预测三维四向编织复合材料的纵向拉伸力学性能与试验值吻合良好,损伤分析结果合理地反映了面胞和内胞的渐进损伤过程。