Experimental investigation and numerical simulation of three-point bending fatigue of 3D orthogonal woven composite

This paper reports the three-point bending fatigue behavior of three-dimensional (3D) orthogonal woven composite (3DOWC) in experimental and finite element analysis (FEA) approach. In experimental, the S–N curve was obtained to illustrate the relationship between applied stress levels and number of cycles to failure. The stiffness variation was recorded to present the degradation of mechanical properties of the 3DOWC during the process of fatigue loading. Furthermore, the fatigue damage morphologies of the tested 3DOWC coupons were given to indicate the damage modes of different parts (resin, yarns, and their interface) of the composite under the range of stress levels. In FEA approach, a user-defined material subroutine UMAT which characterizes the stiffness matrix and fatigue damage evolution of the 3DOWC was developed and incorporated with a finite element code ABAQUS/Standard to calculate the maximum deflection of the 3DOWC during each loading cycle. The bending deformation at different loading cycles was also calculated. From the comparisons between FEA and experimental approaches, it is indicated that the proposed model is reasonable for calculating the fatigue bending deformation.     

Large-scale finite element analysis of a 3D angle-interlock woven composite undergoing low-cyclic three-point bending fatigue

This paper reports the large-scale finite element analysis (FEA) of a 3D angle-interlock layer-to-layer woven composite material undergoing low-cyclic three-point bending fatigue at microstructure level. A microstructure geometrical model of the 3D woven composite material was established to model the real structure of the woven composite. The fatigue behaviors of the 3D woven composite undergoing three-point bending with sinusoidal wave-form were investigated from experimental and FEA approaches. Based on displacement-controlled bending and inelastic hysteresis energy fatigue damage criterion, the interior deformation, energy absorption, and stress distribution characteristics during the fatigue process were analyzed. The different failure mechanisms and damage patterns of yarns and resin were discussed. The influence of the 3D woven structure on the fatigue behaviors was discussed. The fatigue damage morphologies and stiffness degradation were obtained to compare with the experimental results. The results show that the most of energy was absorbed by warp yarns. Stress concentration was emerged on the inclined part of warp yarns and the interface between yarns and resin. The damage morphologies from experimental and FEA results are in good agreement. The stiffness degradation curves also show the same tendency.     

A composite model for wheat flour dough under large deformation

The mechanical behaviour of dough, gluten and starch were studied in an effort to investigate whether bread dough can be treated as a two phase (starch and gluten) composite material. Mechanical loading tests revealed rate dependent behaviour for both the starch and gluten constituents of dough. There is evidence from cryo-Scanning Electron Microscopy (SEM) that damage in the form of debonding between starch and gluten occurs when the sample is stretched. In addition, a reasonable agreement is seen between the Lodge material model and the compression test data only, indicating again that possibly ‘damage’ is essentially debonding which does not occur under compression, unlike tension and shear loading. A composite finite element model was developed using starch as filler and gluten as matrix. The interface between the starch and gluten was modelled as a cohesive contact interaction. When the interaction of starch and gluten is strong, as indicated for the dough with no damage, the stress-strain curve is always higher than the gluten stress-strain curve under both tension and shear loading. In contrast, when damage is activated in the form of debonding, the dough stress-strain curves under tension are seen to cross over the curves for gluten and therefore leading to lower stress values than in gluten. No damage/debonding occurs under compression when a damage function is used which is in good agreement with the experimental data.     

Mechanical properties and microstructure of 3D sinking woven quartz fiber-reinforced silica composites by silicasol-infiltration-sintering

Three-dimensional (3D) sinking woven quartz fiber-reinforced silica composites were successfully prepared by silicasol-infiltration-sintering process at a low temperature of 450°C. The density of the composites was 1.74?g/cm³. The characteristics of 3D sinking woven structure were determined. Flexural strength and shear strength of the composites were investigated along the warp and weft directions. Both flexural stress–displacement curves in warp and weft directions had two fractural points, e.g. matrix fracture point and fiber fracture point. The shear stress–displacement curves exhibited mostly nonlinear behavior. The composite in warp and weft direction reflects different shear behavior. Microstructural observations revealed that the adhesion strength between the fibers and the matrix was weak. There was a good state without serious degradation of quartz fibers during the preparation. Apart from these, the composites exhibited an extensive and long fiber pullout in the fracture surface. Crack deflection and fiber pullout contributed to the good toughness of the composites under the loading.     

Mechanical properties improvement of silane addition epoxy/3D orthogonal woven composite material

In this study, the influence of silane addition on mechanical properties of epoxy/3D orthogonal glass fiber woven composite was studied. The KH560 silane modification composite specimen reinforced with 3D orthogonal woven fabric/epoxy was manufactured by means of Resin Infusion under Flexible Tooling. The mechanical properties of the epoxy/3D glass fiber woven composites were characterized by tensile and bending tests. The tensile and bending properties of silane-modified 3D orthogonal woven glass composite in warp and weft directions were compared with the pristine or epoxy/glass composite material not coupled using silane. The results show that the tensile and bending properties in warp and weft directions have been improved due to the silane addition. The bonding strength between the fiber and matrix was improved and the delamination and debonding between fiber and matrix was retarded and shifted to cohesive failure of the matrix due to the silane modification. Electron microscopy of the fracture and failure modes of the test specimens were used to support the results and conclusions.     

Quasi-static compression and compression–compression fatigue characteristics of 3D braided carbon/epoxy tube

This study presents an experimental study of the quasi-static axial compression and compression–compression fatigue behavior of a three-dimensional braided carbon/epoxy composite tube. Three kinds of tubes with different braiding angles, i.e. 25º, 35º, and 45º were used to examine the dependence of fatigue behavior on the braiding parameters. Quasi-static compression and compression–compression cyclic loadings were carried out on the braided composite samples. The S–N [stress and number of cycles to failure] curves, strain–N (number) curves, and damage observation were used to evaluate the behavior of the braided tubes under fatigue loading. The test results showed that braiding angle had significant effect on the ultimate compression strength (UCS) and the number of cycles per stress level that the sample could withstand. The tube with 25º braiding angle had the highest UCS while the tube with 45º braiding angle accumulates high number of cycles for the same stress level as compared to other samples. Damage occurred along the braid angle for 25º tubes while matrix crack plus bulging occurred in the tubes with 35º and 45º braiding angles.     

Finite element analyses of stress distributions of three-dimensional angle-interlock woven composite subjected to three-point bending cyclic loading

This paper presents the finite element simulation of stress distribution features of 3D layer-to-layer angle-interlock woven composite undergoing three-point bending cyclic loading. With the finite element analysis model, a microstructure shell element model of the woven composite at yarn level was established to calculate the fatigue behaviors and stress distribution during cyclic loading. The stress distributions in the warp, weft yarns, and the resin regions have been calculated to show the stress difference in the woven composite. It has been observed that the warp yarns share the most part of the stress or loading, i.e. the strength warp yarn is more important than that of the weft yarn for the fatigue design. In addition, the stress distributions at the locations where the weft yarns crossover the warp yarns have been investigated. The stress degradations of the top and bottom surface of the woven composite panels were also compared with those in experimental and good agreement was found. With the stress distribution in the woven composite, the method of improving the fatigue damage tolerance was expected to be developed.     

电动门窗升降器用钢丝绳疲劳断丝分析

电动门窗升降器用钢丝绳在使用过程中过早发生断丝。采用扫描电镜、能谱仪对断裂钢丝进行失效分析,并进行疲劳模拟试验。研究表明:钢丝绳在电动升降器上整体发生断裂属于宏观高应力低周弯曲疲劳断裂,弯曲的结构来自于结构组成件上的局部弯曲,弯曲载荷相对于拉伸载荷在应力分布上具有极大不均匀性,会大幅度提高局部的工作应力,引发相关的疲劳开裂。给出预防措施:(1)在安装过程中,避免电动升降器钢丝绳承受弯曲载荷、各股受力不均匀;(2)钢丝绳在铆接头时避免产生严重的弯曲变形或铆接头内孔端头和滑板卡槽处变形;(3)钢丝绳和电动门窗升降器组成件在生产运输过程中避免碰撞、挤压、磨损。     

三维六向编织SiCf/SiC复合材料的力学行为及其损伤机制

为解决陶瓷基复合材料在服役过程中因拉伸和弯曲导致的失效问题,以三维六向编织SiC_f/SiC复合材料为研究对象,分析了受力过程中复合材料力学行为与纤维及结构的联系机制。采用微计算机断层扫描技术获得材料结构及孔隙的三维图像,对复合材料纵向和横向进行拉伸、弯曲性能测试,并阐明其损伤机制。结果表明:复合材料呈现明显的各向异性特性,纵向拉伸强度和弯曲强度分别是横向的10.37、5.06倍;复合材料不同方向受力的损伤模式不同,拉伸载荷下纵向试样裂纹沿着六向纱呈Z字形扩展,而横向试样裂纹沿着编织轴向扩展,最终导致拉伸破坏;弯曲载荷下裂纹沿着厚度方向扩展,并最终导致纵向及横向试样的韧性断裂,且纵向韧性优于横向。     

高性能纤维的单纤维压缩弯曲性能

选取11种高性能纤维,包括PBO纤维、芳纶1313纤维、对位芳纶纤维、高强聚乙烯长丝和高强聚乙烯短纤等,采用单纤维压缩弯曲仪测试纤维的单纤维压缩弯曲性能,并对其压缩弯曲曲线进行对比分析。结果表明,11种高性能纤维中,Technora纤维的最大力和抗弯刚度最大,在相同条件下,Technora纤维更难被压弯;PBO纤维普通丝的抗弯刚度远大于高模量丝的抗弯刚度;直径相同的条件下,芳纶1414纤维的最大力、等效弯曲模量及抗弯刚度明显高于芳纶1313纤维;超高分子量聚乙烯纤维的压缩弯曲曲线变化趋势最明显。     

三维正交机织复合材料的冲后压缩性能

为揭示纱线张力对三维机织复合材料抗冲击及冲后压缩性能的影响规律,基于多剑杆织造工艺,配置不同接结纱张力(25、50、100 cN)织造三维正交机织物,通过真空辅助树脂传递模塑成型工艺制备复合材料,并在室温下进行低速冲击及冲后压缩性能测试。结果表明：当接结纱张力为100 cN时,试样在冲击载荷下发生表层树脂大面积破裂和剥离并使纬纱失去支撑,同时,试样表层纬纱发生较大卷曲,促使压缩载荷发生屈曲失效;接结纱张力为100 cN试样的压缩性能相比接结纱张力为25 cN试样下降约50%;接结纱张力较高时易导致纬纱卷曲增大和树脂富集,并由此降低试样的弯曲刚度和冲后压缩性能。     

体积含量对织物/水泥复合材料弯曲性能的影响

采用无碱玻璃纤维机织物,制备了不同体积含量的织物增强水泥基复合材料,通过三点弯曲抗折强度试验和断裂面形貌数码照片分析,研究了织物体积含量对机织物增强水泥基复合材料弯曲性能的影响。研究结果表明,玻璃纤维机织物体积含量从1%上升到5%时,织物增强水泥复合材料全载荷挠度曲线的形状和弹性模量没有明显变化,经向抗折强度从8.5 MPa上升到17.8 MPa,纬向抗折强度从8.1 MPa上升到17.2 MPa,但增加的幅度与聚合物基单向复合材料纵向强度的混合定律不相符,断裂能从0.53 kJ/m2上升到1.89 kJ/m2,且增加的幅度明显增大。     

基于混合韦伯分布的碳纤维针刺毡结构表征

为研究碳纤维针刺毡的结构并对其参数化表征,基于混合（Weibull）分布分析了3种碳纤维针刺毡的结构参数。对碳纤维针刺毡的纤维长度分布进行了拟合,并分析了造成纤维长度分布规律不同的原因。采用纯弯梁模型模拟碳纤维在针刺毡中的弯曲状态,并对弯曲参数进行了统计分析。结果表明,采用混合Weibull分布模型分析碳纤维针刺毡的内部结构,可真实反映参数指标的分布规律。无论是纤维长度还是纤维的弯曲参数,拟合曲线都有较高的拟合度。此外,采用纯弯梁模型模拟弯曲的碳纤维,不仅可以模拟纤维在针刺毡中的弯曲形貌,还可以将测量结果用于碳纤维针刺毡的参数化建模。     

纺织纤维的弯曲疲劳理论及其应用

为了更加真实地了解纤维的使用性能,合理利用纺织纤维,本文根据现阶段对纺织纤维疲劳机理的研究,部分总结了关于纺织纤维弯曲疲劳的一些研究方法和研究装置。目前对柔性纤维弯曲疲劳的研究,主要有应力寿命(S-N)法、能量法和高聚物疲劳理论,这些对于纺织材料的弯曲疲劳研究都发挥着极其重要的作用。同时,随着理论方法的发展,相应的弯曲疲劳仪器也有了很多的改进。结合现代一些专业软件的开发应用,纤维疲劳研究的内容和方法越来越方便和真实,这些都有效促进了纺织纤维弯曲疲劳的研究发展。     

三维角联锁机织复合材料三点弯曲破坏的有限元计算

为了说明一种层层接结三维角联锁机织复合材料在三点弯曲载荷下的动态响应以及结构破坏行为,运用有限元分析软件ABAQUS,在纱线、基体细观结构尺度上计算与考察材料在一恒速弯曲应力作用下的挠度随时间的变化历程、渐进破坏过程、应力分布以及应力集中区域的结构效应。通过分析计算结果发现：三维角联锁机织复合材料的三点弯曲破坏与其结构特征密切相关,破坏由结构中的应力集中区域萌发。此外,应力集中部位主要位于屈曲波浪状的经纱上,且处于各根经纱的弯折部位。这种结构特征使其在材料承载过程中受到的载荷最大,从而导致破坏的进一步扩展。     

锯齿形三维机织间隔复合材料的弯曲性能

为解决层合间隔复合材料易开裂和整体性差的问题,采用绿色环保的玄武岩低捻长丝作为经、纬纱,合理设计经向截面图和组织图,并在普通织机上织造3种不同间隔高度的锯齿形三维机织间隔织物。以所织得的锯齿形三维机织间隔织物作为增强材料,环氧乙烯基树脂作为基体,利用真空辅助成型工艺,制备锯齿形三维机织间隔复合材料,同时对三维机织间隔复合材料进行三点弯曲性能测试,得到弯曲载荷-位移曲线、能量吸收图和破坏模式。结果表明:复合材料的纬向是主要承力方向;组织循环个数越多的材料表现出更好的弯曲性能;在一定间隔高度范围内,间隔高度越高的锯齿形三维机织间隔织物承受的弯曲载荷和吸收的能量也越高;锯齿形三维机织间隔复合材料的破坏模式是材料上表层受压,下表层受拉,而连接层受压;在作用力下材料只是出现明显的变形,但并未出现材料整体的破坏。     

单向复合材料冲击破坏模拟

为了说明单向复合材料在高速冲击下的破坏行为,为抗冲击材料的结构设计提供指导。通过有限元模拟分析的方法,在纱线与树脂基体尺度上计算单向复合材料在不同冲击速度下的响应与破坏。对比分析不同冲击速度下材料上某特殊位置点的挠度变化曲线、应力变化曲线以及材料破坏形态等方面,说明单向复合材料的抗冲击行为。在高速冲击作用下,由于冲击能量被靶体的吸收与耗散,单向复合材料的应力及变形幅度随着时间的延续越来越小;此外,树脂碎裂、纱线的断裂抽拔是单向复合材料在高速冲击下的主要破坏模式。且由于受力模式的不同,材料下表面的破坏程度比上表面更为剧烈。     

改性聚乙烯醇纤维增强水泥基复合材料制备及其力学性能

为提高聚乙烯醇(PVA)纤维与水泥基体间的界面强度,采用化学接枝法在PVA纤维表面接枝一层纳米二氧化硅颗粒(SiO₂ NPs),制备改性PVA纤维增强水泥基复合材料(PVA-FRCC)。通过三点弯曲试验测试改性前后PVA-FRCC的抗弯强度,并研究纤维铺排方向和层数对水泥基复合材料抗弯性能的影响。结果表明:纤维交叉铺排时,PVA-FRCC的抗弯强度优于纵向和横向铺排,且改性PVA-FRCC的抗弯强度高于未改性PVA-FRCC的;当纤维铺排层数为3层时,改性PVA-FRCC的抗弯强度最好。对PVA-FRCC的弯曲过程进行有限元模拟分析,含有横向铺排纤维的PVA-FRCC断裂失效时,纤维的桥连作用突显。同时,交叉铺排的PVA-FRCC中除横向铺排的纤维承力外,纵向纤维也有一定的承力,且试样失效后无界面损伤。     

Impact performance of two bamboo-based laminated composites

The present work aims to determine the impact performance of two bamboo-based laminated composites [bamboo/poplar laminated composite (BPLC) and bamboo/glass fiber laminated composite (BGFLC)] using low-velocity impact tests by a drop tower. In addition, fracture characteristics were evaluated using computed tomography (CT). Results showed that BPLC presented better impact properties in both directions than BGFLC. Three stages are noted in impact load–deflection curves. The load–deflection curve characteristics of two composites are different in different stages. Matrix cracking, fiber-matrix interface debonding and delamination, and fiber breakage are the three main fracture mechanisms of two composites. Structural characteristics of the components and bonding strength are the important factors for impact properties and fracture mechanism of both bamboo-based laminated composites.     

应用高温高压镶嵌法的超疏水涤纶织物制备

为开发制备超疏水涤纶织物的短流程工艺,研究了高温高压下在涤纶表面镶嵌聚二甲基硅氧烷(PDMS)制备方法。结果表明：PDMS对涤纶表面的镶嵌作用能赋予涤纶超疏水性,水接触角能达到163.4o,滚动角最小可达7.0o,沾水等级达到5级,同时改性涤纶织物具有优异的耐洗性能。电镜观察表明,涤纶原有纤维棱角变模糊,表面粗糙度提高;红外光谱分析表明PDMS成功镶嵌到涤纶纤维结构中;X-衍射及DSC分析表明纤维主体结构基本不变;改性后涤纶织物断裂强力有所下降,折皱弹性有小幅度增加,抗弯刚度、白度基本无变化。该方法工艺流程短、成本低、效果好,具有良好的应用前景。