纤维铺层角度对复合材料薄壁圆管轴向压溃吸能特性影响研究

研究T700/3234复合材料薄壁圆管轴向压溃吸能特性受纤维铺层角度变化的影响规律。开展复合材料力学性能试验和薄壁圆管轴向准静态压溃试验。通过对比圆管轴向压溃峰值载荷及比吸能等指标的试验结果,验证建立的复合材料圆管有限元模型和分析方法。基于验证的有限元分析方法,探讨了复合材料纤维铺层角度的变化对薄壁圆管轴向压溃吸能特性的影响规律。结果表明,在准静态轴向压缩载荷下,随着纤维铺层角度的增大,比吸能先增大后减小;纤维角度为±45°时,初始峰值载荷最低,载荷效率最高,圆管易于进入渐进破坏吸能阶段。研究结果可为复合材料纤维铺层角度设计及复合材料薄壁结构有限元建模提供参考。     

铺层顺序对复合材料薄壁圆管轴向压溃吸能特性的影响研究

采用仿真和试验相结合的方法探讨复合材料薄壁圆管在准静态轴向压缩载荷下的失效吸能特性和吸能机理。首先,建立复合材料薄壁圆管"层合壳"有限元模型,通过显式动力学方法求解其在准静态轴向载荷下的压溃失效力学行为。仿真与试验结果在圆管轴向压溃变形过程、初始峰值载荷、平均压溃载荷及比吸能等主要吸能参数上具有很好的一致性,验证了"层合壳"复合材料圆管有限元模型和建模方法的有效性。其次,采用解析模型与仿真分析方法分别对[0/90]_3s、[0/90/0₂/90₂]_s、[0₃/90₃]_s三种不同铺层顺序的复合材料圆管的屈曲载荷与吸能特性进行了对比,进一步分析了铺层顺序对圆管失效吸能特性的影响。研究表明,0°与90°铺层交替程度对复合材料圆管的吸能特性影响较大,保证纤维失效方式在结构宏观失效中占主导地位能够提高材料失效吸收能量。     

碳纤维增强环氧树脂复合材料圆管多胞填充结构吸能特性的准静态压缩试验

针对现有研究对复合材料多胞结构吸能特性研究的不足,提出了一种由多根小尺寸的单根碳纤维增强环氧树脂复合材料圆管(Single CFRP tube,SCT)填充进大尺寸碳管组成的多胞填充结构(Multicellular filling structure,MFS),并分别对SCT和MFS进行了单次全行程加载和多次分段加载的准静态压缩,分析了其压缩破坏模式和吸能特性。研究结果表明:MFS最外侧碳管破坏模式与SCT破坏形式相似,且单次全行程压缩与多次分段压缩的破坏模式没有明显区别,但MFS最外侧碳管由于内部碳管及碎屑的挤压呈现出明显的径向变形;相对于单次全行程压缩过程,SCT及MFS多次分段压缩时的总耗能量更多;本次研究的SCT试件最大比吸能为86.0 J/g,最小比吸能为59.3 J/g,然而由于MFS最外侧管件的比吸能低,导致其比吸能在69.8~75.9 J/g之间,小于单管根碳管的最大比吸能,但进一步研究可知,合适的外部约束形式和内部碳管数量可使MFS比吸能高于SCT的最大比吸能。      

含随机不确定参数复合材料薄壁结构吸能特性评估方法研究

针对复合材料力学性能分散度大、加工精度低,导致复合材料薄壁吸能因素不确定等,提出含随机不确定参数复合材料薄壁结构吸能特性评估方法。考虑材料力学性能及结构特征尺寸的不确定性,评估准静态压溃条件下薄壁圆管峰值载荷及比吸能指标。据试样级材料性能实验确定各参数分布特征;用Plackett-Burman方法选实验点,采用显式求解有限元方法分析选出对比吸能、峰值载荷影响显著的参数;建立影响显著参数及结构吸能特性指标间二阶响应面函数;据参数分布抽样计算获得吸能特性指标分布情况。结果显示,对复合材料薄壁圆管而言,纤维方向拉伸、压缩强度及圆管壁厚、基体压缩强度对其轴向压溃的比吸能及峰值载荷影响显著。     

复合材料层合结构破坏机理及压溃吸能特性分析

针对纤维增强复合材料层合试验样件,对[90]_(16)和[0]_(16)试验样件分别进行拉伸、压缩试验,对[±45]_(4s)试验样件进行剪切试验,分析其破坏模式,通过SEM扫描电镜观察试验样件断口微观形貌,揭示其细观破坏机理。针对纤维增强复合材料层合薄壁结构,对[±45/0/0/90/0]_s圆管、[0/90]_(3s)圆管、[0/90]_(3s)方管和[±45]_(3s)方管进行准静态轴向压溃试验,分析其宏观破坏模式及吸能特性。结果表明:宏观破坏模式是多种细观破坏机理共同作用的结果,包含纤维断裂、基体变形与开裂、层间与层内裂纹扩展等;[±45/0/0/90/0]s圆管为横向剪切破坏模式,比吸能最大;[0/90]_(3s)圆管为层束弯曲失效模式,比吸能次之;[0/90]_(3s)方管为层束弯曲失效模式,比吸能第三大;[±45]_(3s)方管为局部屈曲失效模式,比吸能最小。不同铺层方式复合材料层合薄壁圆管和方管压溃破坏失效模式差异较大,比吸能差距也较大,通过合理设计可以改变复合材料层合薄壁结构破坏模式,改进其吸能特性。     

基于声发射技术的三维编织复合材料压缩破坏分析

基于声发射(AE)技术研究了不同编织角度的三维四向炭/环氧编织复合材料在压缩载荷作用下的破坏过程。分析了累积声发射能量,事件率,幅值和波形经过快速傅里叶变换后的峰值频率。同时,结合载荷-位移曲线,把破坏过程分成不同的阶段来深入理解编织复合材料的破坏机理。用光学显微镜观测试件的破坏表面。结果表明AE参数能很好地描述三维编织复合材料的破坏过程,而且破坏机理也可用AE特性来识别。     

纤维缠绕复合材料夹芯圆柱体准静态压缩吸能机制

提出并设计了一种新型纤维缠绕复合材料夹芯圆柱体吸能结构单元。为探讨其在准静态压缩载荷作用下初始损伤的产生、扩展及演变规律,基于ABAQUS建立该单元数值分析模型,并开展了准静态压缩试验。数值模拟与试验现象综合分析表明,准静态压缩载荷作用下单元结构的响应具有三阶段特征,包括初始线弹性压缩阶段、渐进损伤阶段和结构破坏阶段。固体浮力芯材在压缩载荷作用下产生塑性损伤变形和剪切断裂破坏,纤维缠绕复合材料表层在芯材横向膨胀效应引起的环向应力作用下发生环向纤维的拉伸断裂破坏,导致单元结构稳态吸能过程的终止。研究结果表明,该单元比吸能效率远高于传统的复合材料圆柱壳结构。     

三维四向编织碳纤维/环氧树脂复合材料在热环境中的拉压力学性能实验

针对不同编织角度的三维四向编织碳纤维/环氧树脂复合材料,进行了热环境下的轴向拉伸和压缩力学性能实验研究,讨论了温度对三维四向编织复合材料的轴向拉伸和压缩力学性能的影响,并根据宏观断裂形貌和SEM图像分析了材料的破坏和断裂机制。结果表明,随着测试温度的升高,三维四向编织碳纤维/环氧树脂复合材料的纵向拉伸强度有小幅提高,而纵向压缩强度显著降低。在室温条件下,编织角对材料的纵向拉伸破坏特征没有影响,而对材料的纵向压缩破坏特征有较大影响。随着测试温度的升高,不同编织角度复合材料的纵向拉伸和压缩的损伤破坏形态均与室温条件下明显不同。      

三维五向炭纤维/酚醛编织复合材料的压缩性能及破坏机制

针对不同编织角、 不同纤维体积分数的三维五向炭纤维/酚醛编织复合材料在不同温度下进行了纵向(编织方向)压缩和横向压缩试验 , 获得了其主要压缩力学性能 , 分析了编织参数、 温度对材料压缩力学性能的影响。对试件断口进行了宏观及扫描电镜观察 , 从宏、 细观角度研究了材料的变形及其破坏机制。结果表明 , 三维五向炭纤维/酚醛编织复合材料的压缩应力2应变曲线呈现明显的非线性特征 , 且温度效应明显; 编织角和纤维体积分数是影响材料压缩性能的主要参数。三维五向炭纤维/酚醛编织复合材料的纵向压缩与横向压缩具有完全不同的破坏机制。      

三维四向编织复合材料压缩力学性能实验研究

通过对三维四向编织复合材料薄板试件的宏观压缩实验,研究了三维四向编织复合材料的抗压力学性能.实验结果表明:材料的编织角对其压缩力学性能的影响很大,随编织角的变化,编织复合材料的压缩破坏机制发生了变化.编织角度较小时,材料表现为脆性特征;当编织角度大于某个临界角度时,材料的应力-应变曲线趋于非线性,更多地表现为塑性破坏.     

碳纤维-玻璃纤维混杂增强环氧树脂三维编织复合材料薄壁圆管压溃吸能特性与损伤机制

基于三维编织成型及真空辅助树脂传递成型技术,制备了编织纱和轴纱不同混杂方式(编织纱/轴纱:碳纤维-碳纤维(CF-CF)、碳纤维-玻璃纤维(CF-GF);玻璃纤维-碳纤维(GF-CF))增强环氧树脂(EP)的三类三维编织复合材料薄壁圆管,通过准静态轴向压溃及详细的破坏断面观察,研究了纤维混杂方式对薄壁圆管的能量吸收性能和破坏模式的影响。研究发现:CF-CF/EP样品的比能量吸收值分别比GF-CF/EP大36%,比CF-GF/EP大12%。编织纱为碳纤维时(CF-CF/EP及CF-GF/EP),圆管的破坏模式均为折叠破坏模式,编织纱采用碳纤维能有效地遏制中央裂纹的轴向扩展,折叠变形的三维结构内部发生了较多细小的微观破坏。而编织纱为玻璃纤维的GF-CF/EP,破坏模式则为开花内外弯曲式,中央裂纹产生,三维结构呈现分层并向圆管内外弯曲。      

Finite element modelling of the progressive crushing of braided composite tubes under axial impact

Composite tubular structures are of interest as viable energy absorbing components in vehicular front rail structures to improve crashworthiness. Desirable tools in designing such structures are models capable of simulating damage growth in composite materials. Our model (CODAM for COmposite DAMage), which is a continuum damage mechanics based model for composite materials with physically based inputs, has shown promise in predicting damage evolution and failure in composites. In this study, the model is used to simulate the damage propagation, failure morphology and energy absorption in triaxially braided composite tubes under axial compression. The model parameters are based on results from standard and specialized material testing and a crack band scaling law is used to minimize mesh sensitivity (or lack of objectivity) of the numerical results. Axial crushing of two-ply and four-ply square tubes with and without the presence of an external plug initiator are simulated in LS-DYNA. Refinements over previous attempts by the authors include the addition of a pre-defined debris wedge, a distinguishing feature in tubes displaying a splaying mode of failure, and representation of delamination using a tiebreak contact interface that allows energy absorption through the un-tying process. It is shown that the model adequately predicts the failure characteristics and energy absorption of the crushing events. Using numerical simulations, the process of damage progression is investigated in detail and energy absorptions in different damage mechanisms are presented quantitatively.     

Investigation on the compressive properties of the three dimensional four-directional braided composites

The compressive mechanical properties of three dimensional (3D) braided composites are of key concern for design in actual engineering application. A representative volume cell (RVC) is chosen to study the uniaxial compressive mechanical properties of the braided composites with different braid angles by combing damage theory and finite element method. The fiber misalignment and longitudinal shear nonlinearity of braid yarn are considered in the computation model. And their influences on the compressive behavior of the braided composites are also evaluated. The damage development of constituents within the braided composites are obtained and analyzed. The main damage and failure modes and their interaction of braid yarn are provided as well. The numerical results are found that the compressive mechanical behavior of the braided composites with lower braid angle is sensitive to the fiber initial imperfection of braid yarn. The strength of the braided composites with different braid angle is controlled by the different microscopic failure modes.     

编织角和承载方向对三维四向编织复合材料动态压缩性能的影响

利用分离式霍普金森压杆（SHPB）装置对三维四向编织碳纤维增强树脂基复合材料的动态压缩性能进行了研究。通过对编织角为20°、30°和45°的试验件分别进行沿纵向、横向和厚度方向的动态压缩试验,得到材料在800~2 000/s应变率范围内的应力-应变曲线,并与准静态压缩试验结果进行对比,研究了应变率、压缩方向及编织角对材料极限强度和弹性模量的影响。结合高速摄影记录的动态压缩过程,进一步分析了不同情况下材料的破坏模式与破坏过程。结果表明：应变率越高,材料的极限强度和弹性模量越大,材料在受压的三个方向上均具有一定的应变率强化效应,且高应变率下表现出比准静态压缩时更明显的脆性;编织角的改变对材料在三个方向上的动态压缩性能均有影响,其中对纵向的影响最为明显;不同方向受压时材料的失效形式不同,且准静态和高应变率下的失效形式也有区别。     

三维编织玻璃/环氧复合材料梁的低速冲击和冲击后压缩性能研究

试验制备了三维编织四向结构、五向结构和六向结构的玻璃纤维预制件增强环氧树脂梁的复合材料试样,每种试样包含20°、30°和40°三个编织角度.研究了编织结构和编织角参数对复合材料低速冲击及冲击后压缩性能的影响,分析了损伤后的试样形貌及破坏情况.试验结果表明:编织参数对复合材料的损伤容限影响较显著;编织角相同时,五向结构具有较高的CAI强度,而六向结构则表现出较好的冲击韧性;编织结构相同时,30°编织角试样的抗冲击性能较好;同时,冲击后压缩试样表现出脆性断裂特征.     

Multi-Scale Progressive Damage Model for Analyzing the Failure Mechanisms of 2D Triaxially Braided Composite under Uniaxial Compression Loads

Based on continuum damage mechanics (CDM), a multi-scale progressive damage model (PDM) is developed to analyze the uniaxial compression failure mechanisms of 2D triaxially braided composite (2DTBC). The multi-scale PDM starts from the micro-scale analysis which obtains the stiffness and strength properties of fiber tows by a representative unit cell (RUC) model. Meso-scale progressive damage analysis is conducted subsequently to predict the compression failure behaviors of the composite using the results of micro-scale analysis as inputs. To research the free-edge effect on the local failure mechanisms, meso-scale models of different widths are also established. The stress-strain curves obtained by numerical analysis are verified with the experimental data. Results show that fiber and matrix compression failure inside the fiber tows are the major failure modes of the composite under axial compression. For transverse compression, the dominated failure modes are recorded for matrix compression failure inside the fiber tows. It is also presented that the free-edge effect plays an important role in the transverse mechanical response of the composite, and the failure behaviors of the internal fiber tows are strongly influenced as well.     

Finite element analyses on transverse impact behaviors of 3-D circular braided composite tubes with different braiding angles

This paper presents finite element analyses (FEA) on the transverse impact responses of 3-D circular braided composite tubes with the braiding angles of 15°, 30° and 45°. A finite element model of the braided composite tube was established at microstructure level to analyze the transverse impact behaviors. From the FEA results, the impact damage, deformation and stress distribution were obtained to analyze the damage mechanism. Stress propagation in lower braiding angle tubes was faster than that of the higher braiding angle. The impact responses of the braided composite tubes were also tested to obtain load–displacement curves and energy absorption for the comparisons with the FEA results. The impact damage and fracture morphology obtained from the FEA were in good agreement with the experimental results, which demonstrated the feasibility of the FEA model for the design of the braided tube.     

Quasi-Isotropic Triaxially Braided Cellulose-Reinforced Composites

In this article, we investigate experimentally and analytically the mechanical properties of a natural fiber quasi-isotropic triaxially braided composite. The composite is prepared from triaxially braided regenerated cellulose fibers and a high-bio-content epoxy resin system using a resin infusion process. Simultaneous mechanical loading, digital image correlation, and acoustic emission tests were performed on notched and unnotched specimens to understand the tensile behavior of the composites and the initiation and propagation of damage. Experimental results were compared with the effective tensile properties determined using an analytical model. The model is a discrete three-layer analytical representation based on a mechanics transformation-based representation of the quasi-isotropic braided layers. The model is used to determine the elastic stiffness and Poisson effects based on the constituent properties such as the fiber volume fractions, the waviness of the bias tows, and the relative thickness of the braided preform. The experimental results show the analytical model's ability in predicting the composite's elastic properties. The unique fabric architecture is found to have a large influence on the strength properties across the different specimen geometries investigated.     

Tensile behaviour of multi-layered braided structures

Multi-layered braided structures are formed as a result of over-braiding the previously formed braids and they are increasingly being used for numerous applications ranging from hoses to energy absorbing composites. In this research work, a series of multi-layered braided structures were prepared on circular braiding machine for obtaining various combinations of braid angles of 30° and 45° in inner and outer layers. Subsequently, the tensile properties of multi-layered braided structures were analysed and it was found that the braid angle in the outer layer has significantly affected the stress–strain behaviour. A simple analytical model for predicting the tensile behaviour of multi-layered braided structures has also been proposed based on the previously developed model of ‘braid-elastic core’ system. A clear distinction has also been made between the helix and braid angles. Furthermore, a comparison has been made between theoretical and experimental values of braid angle, toughness and stress–strain characteristics of multi-layered braided structures.