复合材料层合板静压痕试验及全过程数值分析

复合材料层合板在静压痕力作用下主要发生层间分层、基体开裂、基体压缩破坏、纤维断裂和纤维压坏这几种损伤模式。本文利用ABAQUS有限元程序,对在静压痕力作用下的复合材料层合板建立一个基于Hashin强度准则的全过程模型,并对各层各单元进行损伤演判。利用有限元模型对碳纤维NCF材料层合板在静压痕力作用下的荷载-位移曲线进行预测,并模拟层合板的损伤全过程,以及预测凹坑深度与静压痕力的关系曲线。对层合板进行静压痕试验,测试复合材料层合板在静压痕力作用下的荷载-位移曲线,并在试验过程中用凹坑深度仪测量层合板的凹坑深度。将数值模拟与试验结果比较,两者结果较为吻合。     

基于拉伸载荷的碳纤维/环氧树脂层合板疲劳断裂机理

为研究拉伸载荷下碳纤维/环氧树脂层合板的疲劳性能，开展了4种应力水平下的T300/6511碳纤维平纹织物层合板的拉-拉疲劳实验，得到了不同应力水平下层合板的疲劳寿命。采用超声波C扫和扫描电子显微镜（SEM）观察断口形貌及内部损伤，讨论复合材料疲劳损伤发展积累过程和断裂机理。通过复合材料疲劳有限元分析模型，模拟了复合材料织物层合板疲劳损伤积累和失效过程，绘制了S-lg N曲线，分析发现模型预测的疲劳寿命及失效模式与实验结果吻合良好。疲劳加载时，层合板两侧自由边的表面首先出现基体开裂和分层损伤，随后诱发基体与纤维间界面破坏，损伤加剧，并迅速向内侧扩展；最后大量纤维和基体断裂，损伤贯穿整个截面，导致疲劳断裂。     

复合材料加筋层合板准静态压痕实验研究及数值分析

利用ABAQUS有限元程序所建立了一种基于用户子程序USDFLD和Hashin强度准则的复合材料损伤计算模型,用该模型对复合材料加筋层合板在静压痕力作用下主要发生的纤维拉伸破坏、纤维微屈破坏、基体拉伸破坏、基体压缩破坏、层间拉伸破坏、层间压缩破坏这几种基本损伤模式进行分析。对复合材料加筋层合板在静压痕力作用下进行损伤全过程数值研究,利用该有限元模型预测复合材料层合板静压痕力作用下的荷载-位移曲线以及凹坑深度与静压痕力的关系曲线。数值仿真与实验结果吻合较好,表明该损伤模型方法的可行性。复合材料层合板加筋后拐点处的凹坑深度明显加大,达到0.84mm。通过对加筋板的刚度和强度失效规律的分析,为进一步的复合材料格栅加筋结构(如飞机结构中复合材料后压力框)的性能分析提供参考。     

复合材料层合板雷击损伤数值模拟研究

复合材料导电性差,雷击损伤严重危及到复合材料飞机结构安全。研究建立了复合材料层合板雷击损伤数值模拟的三维有限元模型。首先给出雷击电流作用下复合材料层合板的热-电耦合控制方程,然后建立基于层合板温度分布的单元失效和材料热电性能衰减准则,通过ABAQUS有限元软件的热电耦合分析模块中添加用户子程序USDFLD实现复合材料层合板雷击损伤数值模拟。预测结果与试验结果对比表明,该模型可准确预测复合材料层合板雷击损伤的损伤形状、面积和深度。     

复合材料层合板低速冲击承载能力的细观力学有限元模型

将复合材料细观力学桥联模型与有限元软件ABAQUS结合,用于分析层合板受低速冲击作用的极限承载能力.通过确定组分材料是否破坏来判断单层板是否破坏,对破坏后的单层实施一种常系数刚度衰减.将细观力学本构模型、针对组分材料的破坏判据以及刚度衰减模式编制成用户子程序VUMAT,为ABAQUS求解层合板的极限冲击响应提供一种自定义材料模型.只需要输入纤维和基体的材料参数、纤维体积含量等有限数据并且无须单层板的实验数据,就能顺利实施复合材料层合板结构的冲击承载能力分析.所计算的层合板的挠度-时间曲线以及横向冲击力-时间曲线与实验值吻合良好,说明本文的方法是有效的.     

碳纤维复合材料引擎盖的轻量化设计

以汽车碳纤维复合材料引擎盖为研究对象，采用碳纤维复合材料为研究材料，以层合板理论为力学数值模拟CAE设计基础，利用ABAQUS软件对单层级试样准静态拉伸试验和典型U形梁结构准静态三点弯试验进行仿真，然后进行了台架模态和抗凹刚度测试。采用概念设计、材料性能试验和工艺设计多阶段联合优化设计的方法，最终在满足各种力学性能和制造工艺要求的前提下，实现碳纤维复合材料引擎盖的轻量化设计。     

双轴向纬编针织复合材料准静态侵彻性能及有限元模拟

本文使用双轴向纬编针织复合材料，利用MIS得出材料准静态侵彻实验的载荷-位移曲线，并计算得出侵彻功-位移曲线。运用有限元方法，模拟整个破坏过程，通过计算得出理论上的载荷-位移曲线和侵彻功-位移曲线。将模拟结果与实验结果进行比较，表明两种分析结果具有较好的一致性，并揭示双轴向纬编针织复合材料准静态侵彻机理。     

准静态压痕作用下复合材料层合板损伤阻抗与损伤容限实验研究

参照标准实验方法,开展了复合材料层合板对准静态压痕力的损伤阻抗和损伤容限实验研究,获取了接触力、压痕深度、压头位移等实验数据,并对含静压痕损伤层合板进行了剩余压缩强度试验。研究了压痕深度-接触力与剩余压缩强度-压痕深度的变化关系,并讨论了准静态压痕过程中的损伤演变过程和层合板的压缩破坏模式。结果表明:当层合板表面出现目视勉强可见压痕时,初始损伤发生,压痕深度随接触力增大而明显增大,同时剩余压缩强度随压痕深度增加而明显降低;当达到最大接触力时,层合板失去承载能力,背面可看到大量纤维断裂。对于含静压痕损伤的层合板,压缩破坏模式为贯穿损伤区域的层合板断裂。     

胶接碳纤维复合材料层合板拉伸性能及有限元模拟

使用自动铺带工艺制得胶接的碳纤维复合材料层压板试验件,通过轴向拉伸测试,测得了整个试验件的载荷-位移曲线和检测点附近的应变-载荷曲线。试验结果表明,在拉伸载荷作用下试件发生层间剪切破坏,由于胶层的剪切强度高于层合板的层间剪切强度,破坏并没有发生在胶接面内,而是发生在胶层以外的层合板的层间。建立了相应的有限元模型,模拟结果和试验结果的一致说明了有限元模型的合理性。     

纤维复合材料层合板在四点弯曲载荷下的损伤分析

实验测试了T300/7901碳纤维复合材料[0/90]_(8s)层合板在四点弯曲静载下的载荷-位移响应及破坏载荷。基于桥联模型,在商用软件Abaqus/CAE中实现对该层合板在四点弯曲静载条件下的层内以及层间损伤破坏进行模拟分析。分析方法分为四个部分:仅利用组分材料数据,基于桥联模型对单向复合材料层的本构关系建模;利用考虑三维应力的Hashin判据预报复合材料层的纤维拉伸、压缩损伤及基体拉伸、压缩损伤;出现组分材料损伤后对相应材料点采用Camando方法进行刚度退化;在复合材料单层中间插入薄的纯树脂层,通过树脂层的损伤破坏分析层间分层。在Abaqus/Explicit模块中,利用子程序VUMAT完成以上材料建模分析;将模拟结果与实验数据进行对比。结果表明,模拟得到的载荷-位移曲线及破坏载荷与实验结果吻合很好,所提出的材料模型能有效预报纤维复合材料层合板的层内及层间损伤破坏情况。     

A study of damage accumulation in unidirectional glass reinforced composites via acoustic emission monitoring

Damage accumulation in continuous unidirectional glass reinforced composites was studied by acoustic emission (AE) monitoring during three-point-bend loading. Results are presented for four composites monitored during quasi-static break loading, and one composite also monitored during cyclic fatigue and static creep loading. AE response was correlated with the mechanical (stress-strain) response and with visual observation of damage events to study the details of the damage accumulation process. Results show that the failure process is characterized by the sequential occurrence of three distinct damage mechanisms. Specifically, the failure process initiated with cohesive matrix damage, propagated with interfacial debonding, and ended with fiber breakage very near catastrophic failure. The same sequential damage process occurred in all four composites and all three test procedures examined. Results also demonstrate that AE analysis, in combination with mechanical testing and microscopic observation, is a valuable tool in understanding damage accumulation in composites.     

含初始脱粘缺陷复合材料加筋壁板渐进压溃过程的数值模拟

建立了预测含初始脱粘缺陷复合材料加筋壁板渐进压溃响应的数值分析模型。该模型综合考虑了复合材料层合板的纤维失效、基体失效和纤维-基体剪切失效三种典型的面内损伤模式,并通过编写用户自定义材料子程序VUMAT实现面内失效类型的判断和相应材料性能的折减;在壁板和筋条连接界面应用虚裂纹闭合技术(VCCT)计算层间裂纹前缘的应变能释放率,并结合B-K混合模式准则控制缺陷的起裂以模拟脱粘的扩展演化过程;采用显式动力学方法准静态分析结构在压缩载荷下的屈曲、后屈曲直至最终压溃的响应过程。数值分析结果与文献试验、数值结果吻合良好,验证了模型的合理性和有效性,并详细研究了复合材料脱粘加筋壁板的损伤演化过程和渐进压溃行为。     

复合材料层合板损伤区域扩展全过程分析

对碳纤维NCF层合板进行了2组准静态压痕试验。第1组采用不同的压头尺寸探究不同压头直径对层合板损伤区域和面积的影响;第2组进行固定压头尺寸的重复试验,使用非接触空气耦合超声波扫描试样损伤情况,研究静压痕力、凹坑深度、损伤面积三者之间的联系。利用Abaqus有限元软件,根据Hashin准则和内聚力单元的结合,对第2组层合板准静态压痕试验进行全过程的损伤扩展分析。分析结果表明,基体拉伸的破坏是层合板最容易出现的破坏,而且其损伤区域涵盖了其他4种损伤区域。凹坑深度与损伤面积存在一定联系,试验开始阶段凹坑增加速度缓慢,损伤面积增加速度较快;接近极限载荷时,凹坑深度增加速度加快,损伤面积增加速度减缓。     

Compressive properties and fracture behavior of ceramic fiber-reinforced carbon aerogel under quasi-static and dynamic loading

The quasi-static and dynamic compressive properties of a ceramic fiber-reinforced carbon (CFRC) aerogel were investigated using a universal test machine and a split Hopkinson pressure bar. The fracture surface of the CFRC aerogel was studied by scanning electron microscopy. Results show that the compressive behavior of CFRC aerogel exhibits a significant strain rate strengthening effect. The quasi-static failure strain is higher than the dynamic failure strain. Under quasi-static compressive loading, the carbon aerogel matrix breaks into small pieces at a strain of 0.75 and fibers separate from the matrix. The deformation of the fibers is not obvious, indicating that fibers suffer little stress. Under dynamic compressive loading, the aerogel matrix shatters into fragments at a strain of 0.62 and shows a “bursting” phenomenon. The high speed compression of gas in the aerogel results in an increase of the internal stress. Fibers bend, break and separate from the matrix, indicating that fibers carry partially the applied loading. The carbon nanoparticles are squeezed closer with nearly no voids remaining after both quasi-static and dynamic compression. The increase of the internal stress and the fracture of fibers lead to strain rate strengthening and earlier fracture of the CFRC aerogel at high strain rates.     

平纹机织玄武岩纤维/环氧树脂复合材料冲击拉伸行为

以常规机织工艺生产织物增强体,以真空辅助树脂转移模塑法(VARTM)制备成型复合材料,研究单层平纹玄武岩长丝增强环氧树脂复合材料在准静态和高应变率加载下的拉伸性能。准静态和高应变率拉伸试验分别在MTS-810.23试验仪和分离式霍普金森拉杆(SHTB)测试系统上完成。试验结果表明该材料的力学性能具有应变率依赖性:随着应变速率的增加,拉伸模量和拉伸强度单调增加,失效应变单调减小,弹性能先增加后减小。材料的失效破坏特征也呈现明显的应变率效应:准静态拉伸时,材料断口整齐,树脂的破碎少,几乎没有纤维的抽拔和经纬向纤维束间的滑移;高应变率拉伸时,材料断口参差错乱,树脂完全破碎,纤维束抽拔严重、相互崩裂和滑移,织物增强体结构的整体性破坏严重。     

Dynamic compressive strength of alumina ceramics

Dynamic (220–510 s^?1) and quasi-static (0.001 s^?1) compression experiments are conducted on alumina ceramics implemented with two types of tungsten carbide inserts, cylindrical and step-shaped. Split Hopkinson pressure bar (SHPB) tests with in-situ, high-speed optical imaging are adopted to capture the damage and failure of ceramic samples under dynamic compression. The compressive strength of alumina ceramic samples with step-shaped inserts is 15%–30% higher than that with cylindrical inserts commonly used in previous studies, under both dynamic and quasi-static loading. Damage occurs first at the two ends of ceramic samples with the cylindrical inserts, followed by edge fracture and splitting cracks penetrating the sample. However, damage is initiated in the sample region away from the sample ends for the step-shaped inserts, and oblique and secondary transverse cracks dominate the failure process. The different damage modes in the case of step-shaped inserts result in the delayed damage initiation and sample failure, and consequently high compressive strengths. Finite element modelling (FEM) of the SHPB tests provides strength and damage evolution features consistent with the experiment using the Johnson–Holmquist (JH-2) model. FEM reveals equivalent, tensile and shear stress concentrations at the two ends of samples with cylindrical inserts. The stress concentrations are responsible for the damage initiation and growth at the sample ends and the following splitting cracks, consistent with the high-speed images. In contrast, homogeneous stress distributions are achieved in the sample with the step-shaped inserts, ensuring simultaneous damage development across the sample. Overall, the step-shaped inserts in conjunction with cylindrical samples can yield reliable strength measurements for ceramics and ceramic-like materials.     

Deformation mechanisms and evolution of mechanical properties in damaged advanced ceramics

We investigated the uniaxial compressive behavior of damaged and intact alumina using quantitative X-ray computed tomography (XCT) analysis coupled with digital image correlation (DIC) for mechanical characterization. Internal three-dimensional crack characteristics such as crack surface area and orientation were quantified using XCT to assess the level of damage. From the quasi-static and dynamic stress–strain results, the primary effects of crack damage are to reduce the initial stiffness and rate of lateral expansion in damaged alumina. With increasing axial strain, crack closure was found to lead to a recovery of elastic properties, in some cases to intact levels, in the damaged specimens. Localized deformation mechanisms related to the crack structure, including lateral crack closure, axial crack opening and closing, and inclined crack sliding, were visualized in-situ and connected to XCT reconstructions. High-speed imaging also revealed a mixed fracture mode for damaged alumina that included axial splitting and failure along pre-existing cracks.     

Low-velocity impact damage in graphite-fiber reinforced epoxy laminates

An experimental investigation was conducted to identify the failure mechanism and to understand damage propagation in compression-loaded composite structures. The tests were conducted on several laminates of different ply orientation with thicknesses that ranged from 0.56 to 0.79 cm. The panels were damaged by 1.27-cm-diameter aluminum spheres propelled normal to the specimen surface at velocities ranging from 30 m/s to 140 m/s. Results indicate that there is significant internal laminate damage due to low-velocity impact with no surface damage. The internal damage consists of delamination and intraply cracking. Three damage propagation modes were identified as causing specimen failure; delamination, axial load-lateral deformation coupling, and local shear failure.     

碳纤维编织复合材料拉伸变形测量及声发射监测

采用声发射和数字图像相关互补技术,结合破坏断口微结构特征,研究碳纤维编织复合材料的损伤变形与失效机理。在复合材料试件拉伸加载的同时,实时获取变形特征和损伤声发射信号,分析复合材料力学响应与位移场、声发射特征的关系。结果表明,复合材料试件实时拉伸位移场、损伤破坏过程的声发射相对能量、撞击累积数及幅度等特征参数反映了复合材料表面变形与内部损伤演化过程。复合材料试件断裂时出现较多高持续时间、高幅度、高相对能量的声发射信号,宏观断口平齐,表现为脆性断裂。