一种三维纺织复合材料的本构关系及其性能分析

本文对一种三维增强纤维复合材料的结构与性能进行了研究.通过对手工纺织的三向纤维增强复合材料的分析,建立了其细观力学模型,并在此基础上导出了反映其宏观力学性能的本构关系,同时采用具有相同纺织结构的试件进行试验,对本文的理论结果进行了验证.此外,通过对三维复合材料与层合板的力学性能进行对比试验,说明三维增强复合材料的综合性能,尤其是层间剪切性能得到了很大的改善和提高.     

T700轴向增强经编织物复合材料力学性能的模拟分析与试验研究

应用一种新型界面元模型研究了复合材料层间剪切损伤。通过引入双线性损伤准则和损伤演化,预报复合材料层间裂纹扩展。轴向增强经编织物复合材料由针织纱线引起的纤维变形(KYD)产生了富树脂区域,基于细观力学理论提出了一种新的研究轴向增强经编织物单胞模型受单向拉伸和剪切时KYD区周围应力分布的方法,得出了单胞在受载时首先在这一区域产生裂纹。对单轴向T700经编织物复合材料进行了三点弯曲性能和层间剪切性能试验测试,分析了经编织物复合材料的力学特性。分别模拟了弯曲性能和层间剪切性能试验,得出了最大预报载荷值与试验值误差小于10%,并基于有限元模型研究了复合材料面内损伤和层间裂纹扩展损伤机制。     

求解具有弱界面的复合材料有效性能的近似模型与边界元法

基于中间层模型,建立了用于描述具有弱界面的多夹杂复合材料的三层嵌入式模型.首先,给出了计算多夹杂复合材料有效性能的公式,随后将三层嵌入式模型分成两种体系得到了相应的细观力学近似方法.此外,针对中间层模型进一步给出了快速多极边界元的基本列式.最后,通过算例验证所提出的两种方法的正确性及有效性,并进一步考察了界面性能对复合材料整体宏观性能的影响.比较结果发现,细观力学近似模型形式简单,易于编程计算,适用于快速预测具有弱界面的复合材料有效弹性性能.而数值算法能够快速有效直观的考察复合材料内部受弱界面影响后的应力分布.算例分析结果表明,当中间层厚度较大而弹性模量较低时,会使得夹杂不再具有增强效果.并且,随着中间层厚度的增加,基体内承担的最大应力也随之增加,从而容易导致复合材料在界面处产生破坏.     

新型热塑性复合材料细观力学与宏观性能的研究

碳纤维增强杂萘联苯聚醚酮(CF/PPEK)和碳纤维增强杂萘联苯聚醚砜(CF/PPES)是一种新型高性能热塑性复合材料,制备方法和力学性能的研究是使其得到广泛应用的基础.本工作研究了两种复合材料的预浸热压成型工艺,对制备的单向复合材料进行了力学性能实验研究,并基于复合材料细观结构周期性假设,建立了一种细观力学模型.该模型建立起了宏、细观场量的联系,实验及理论计算结果表明该模型能够较好的预测此种复合材料的宏观弹性性能.     

双斜接修补复合材料层合板的拉伸行为及影响因素双斜接修补复合材料层合板的拉伸行为及影响因素

基于试验和有限元数值方法对双斜接修补碳纤维增强聚合物（CFRP）复合材料层合板在拉伸载荷作用下的力学行为开展研究。通过试验分析了两种不同厚度的双斜接修补复合材料结构的承载能力和失效形式。结果表明,对于不同厚度的双斜接修补复合材料结构,失效强度接近,主要破坏形式均以胶层内聚破坏为主,伴随局部的90°基体开裂。利用连续介质损伤力学模型和内聚力模型分别对复合材料和胶层失效进行描述,通过数值方法开展双斜接修补结构的强度预测和损伤演化分析。数值结果与试验吻合较好,并且指出复合材料基体开裂起始早于胶层失效。通过有限元模型讨论了附加层、双斜接内部尖端所处位置和修补胶层参数对修补性能的影响。      

不同孔隙率CFRP层合板静态力学性能研究

为了研究孔隙率对织物碳纤维/环氧树脂复合材料层合板静态力学性能的影响规律,分别测量了孔隙率为0.33%至1.50%的CFRP层合板的弯曲强度和层间剪切强度,并进行有限元模拟.在适用于复合材料单向板的改进Hashin失效准则基础上,建立了适用于织物纤维增强复合材料静态力学强度的失效准则.通过引入复合材料基本强度参数预测不同孔隙率CFRP层合板的力学性能,结合刚度突然退化模型,采用ABAQUS软件建立了有限元模型.试验结果表明,随着孔隙率的增加,复合材料层合板的弯曲强度和层间剪切强度均呈下降趋势.有限元模型较为准确地预测了不同孔隙率织物碳纤维/环氧树脂复合材料层合板的弯曲强度和层间剪切强度.     

复合界面层对SiCf/SiC复合材料力学损伤行为的影响

SiC_f/SiC陶瓷基复合材料在航空航天领域具有广阔的应用前景,其界面层设计是研究重点。研究表明,复合界面层可以有效提升陶瓷基复合材料的抗氧化性能,但其对材料力学性能及损伤机制的影响尚不明确。本研究利用化学气相渗透法(CVI)制备得到具有BN及(BN/SiC)₃复合界面层的小复合材料,探究了复合界面层对SiC_f/SiC复合材料失效机制的影响。基于两种力学加载实验结合声发射探测分析了两种界面层小复合材料的损伤过程。实验结果表明,利用CVI制备的小复合材料界面结构清晰,基体致密。两类小复合材料均具有SiC_f/SiC陶瓷基复合材料的典型力–位移曲线,不同界面层小复合材料损伤过程具有不同的力声特征。通过两类力学加载试验的声发射特征能够有效分析小复合材料各阶段损伤发展情况。本实验中BN及(BN/SiC)₃复合界面层SiC_f/SiC小复合材料最大承受载荷分别为139和160 N,复合界面层小复合材料中的多层界面具有更强的偏转裂纹能力,降低裂纹延伸至纤维的速度,进而提高...     

纤维复合材料粘弹性动态性能的细观力学分析

建立了纤维增强复合材料粘弹性动态性能的细观力学模型.首先建立了树脂基体相各向同性的粘弹性模型,模型参数由纯树脂基体材料的蠕变试验获取,在此基础上分别建立了针对单向和正交铺层复合材料的横观各相同性、正交各相异性的细观粘弹性模型.对单向、正交铺层复合材料进行了静态和动态试验,分别通过试验和上述理论模型得到了其阻尼比、动态储存模量、损耗模量和损耗因子,理论预测与试验结果吻合.     

Glass/Epoxy复合材料叠层板面内剪切连续损伤模型

为确定S2玻璃纤维/环氧树脂(S2-Glass/Epoxy) 叠层复合材料面内剪切应力-应变关系,对S2-Glass/Epoxy 叠层复合材料面内剪切拉伸载荷下的弹、塑性连续损伤本构模型及应用进行了研究。基于平面应力状态下的连续损伤力学模型,通过典型面内剪切拉伸实验,分别建立了忽略塑性应变和考虑塑性应变的两种连续损伤力学(CDM)模型,并确定相关参数。通过ABAQUS/Explicit 用户子程序VUMAT接口,分别采用两种CDM模型对S2-Glass/Epoxy 叠层复合材料面内剪切拉伸实验进行有限元数值计算,与实验结果对比,验证模型可靠性,并分析单元类型对有限元计算结果的影响。研究结果表明: 忽略塑性应变的CDM模型可以很好地预测复合材料面内剪切失效强度,但不能较好地预测其非线性力学响应; 考虑塑性应变,将塑性硬化与损伤耦合后的CDM模型则能较好的预测复合材料非线性力学响应和面内剪切失效强度; 该平面应力状态下建立的CDM模型可用于壳单元进行复合材料有限元数值计算,横向剪切作用导致传统壳单元数值计算的载荷位移曲线略低于平面应力单元计算结果; 减缩积分算法有利于提高有限元数值计算结果的准确性。     

三维编织复合材料的力学性能研究现状

对近年来关于三维编织复合材料力学性能的研究方法和内容进行了综述.归纳出三类主要研究方法:实验研究、细观结构力学模型研究、数值仿真研究.实验研究集中于测试各种编织参数和载荷对其力学性能指标的影响.细观结构力学模型研究主要是通过三维编织体的拓扑结构建立力学分析模型,主要是"米"字枝状模型、纤维倾斜模型和3细胞模型.数值仿真研究是基于材料的线弹性力学,利用有限元分析法对其力学性能进行数值仿真.本工作对当前研究的关键问题进行了分析,就今后的研究工作发表了一些看法.     

Numerical study of the influence of particle-cracking to the damage of MMC by the incremental damage theory

Based on the incremental damage theory, the influences of particle-cracking damage and its residue strengthening capacity on the stress–strain response of particle reinforced (metal matrix composite) MMC under uniaxial tension are carefully investigated in this paper. Two kinds of models are adopted in the numerical calculation to predict the damage evolution of MMC, one is modeling the broken particles as voids and the other is considering the remaining load carrying capacity of the damaged particles. Special emphasis is placed on the detailed comparison between the results predicted by the two models under different parameters such as the aspect ratio, volume fraction of particle and the elastic–plasticity properties of matrix. The damage process of MMC and the development of stress in the particles are predicted by two models and carefully analyzed.     

Fracture toughness analysis of inclined crack in cylindrical shell repaired with bonded composite patch

Adhesively bonded composite patch repair has been widely used to restore or extend the service life of cracked structural components due to its efficiency and cost-effectiveness compared to mechanical repair technique. Current available knowledge on patch repair mainly focus on flat damaged structures and the corresponding analysis methods and empirical databases are computationally efficient. In contrast, only limited work has contributed to studying patch repair to curved damaged structures. Authors have developed an adhesive element in conjunction with a shell element to investigate the effect of curvature on the adhesive stresses and mode I fracture toughness of the cracked host shell in the curved repairs. In this paper, this technology is again employed to model an adhesively bonded composite patch repair to a cylindrical shell embedded with an inclined through-thickness crack. The total strain energy release rate (SERR), calculated by the modified virtual crack closure technique (VCCT), is used to evaluate the mix-mode fracture toughness of the damaged structure and further to estimate the efficiency of patch repair. An automatic mesh generation scheme is proposed to conduct a quick parametric analysis, which can also be used to structural optimization design of composite patch repair. The numerical results are presented to show the effect of curvature and inclined angle of the through-thickness crack on fracture toughness of the repaired structure subject to different loads.     

A study on low velocity impact damage evaluation and repair technique of small aircraft composite structure

Composite structures are very prone to damage at fairly modest levels of impact energy due to foreign object damages. A repair technique using external patch is recognized as an effective method to recover the damaged structures during service life. This work is focusing on the impact damage evaluation and the external patch repair techniques of the aircraft composite structure. The impact damages of composite laminates of the carbon/epoxy UD laminate and the carbon/epoxy fabric face sheets-honeycomb core sandwich laminate are simulated by the drop-weight type impact test equipment. The damaged specimens are repaired using the external patch repair method after removing the damaged area. The compressive strength test and analysis results of the repaired impact damaged specimens are compared with the compressive strength test and analysis results of the undamaged specimens and the impact damaged specimens. Finally, the strength recovery capability after repairing is investigated.     

Analysis of cracked steel members reinforced by pre-stress composite patch

Pre‐stress bonded composite patch is a promising technique to reinforce steel member damaged by fatigue. The effectiveness of this technique was verified by fatigue tests on notched steel plates. Results showed that the application of carbon fibre reinforced plastic (CFRP) strips and, eventually, the introduction of a compressive stress by pretension of the CFRP strips prior to bonding produced a significant increment of the remaining fatigue life. In this paper, the stress intensity factor in the notched plates is computed by a two‐dimensional finite element model in connection with the three‐layer technique in order to reduce the computational effort. Due to high stress concentration at the plate crack tip, debond is assumed at the adhesive–plate interface. The goal is to illustrate the influence of some reinforcement parameters such as the composite strip stiffness, the pre‐stress level, the adhesive layer thickness and the size of the debonded region on the effectiveness of the composite patch reinforcement.     

Fracture analysis of Kevlar-49/epoxy and e-glass/epoxy doublers for reinforcement of cracked aluminum plates

Adhesively bonded composite patch repair is efficient means to regain load carrying capacity, alleviate the crack growth, and improve the service life of the damaged structure. In this paper, three dimensional finite element models are developed to examine the fracture behavior of a single edge V-notched Aluminum plate repaired with Kevlar-49/epoxy or e-glass/epoxy pre-preg patches on both sides. Contour integral method was used for evaluating the stress intensity factor (SIF), an indicator of the crack stability. The load transfer mechanisms, stress distribution, damage variable (D), and crack mouth opening displacement (CMOD), were also presented to estimate the effectiveness of composite patch repair. The influence of the patch material, crack length and the adhesive thickness has been investigated. Results have shown that the crack induced damage increased nonlinearly with a larger crack size. With the composite patch repairs, SIF is reduced to 1/7–1/10 of that of the bare plate and CMOD decreased by 79%. The damage variable is reduced significantly and the load capacity is increased. A thinner adhesive layer results in a higher percentage of load shared by the composite patch.     

Numerical analysis of the patch shape effects on the performances of bonded composite repair in aircraft structures

In this study, the three-dimensional finite element method is used to analyze the effects of the patch shape on the efficiency end the durability of bonded composite repairs of aircraft structures. The stress intensity factor at the crack tip is used as fracture criteria. The determination of this factor allows us to estimate the repair efficiency. The analysis of the stresses distribution in the adhesive layer allows us to estimate the durability of the adhesion between the damaged plate and the composite patch. The obtained results show that the repair performances are closely related to the patch shape. It was demonstrated that the rectangular shape of the patch could be improved using an “H” shape of the patch. This last shape could also be improved using an arrow shape.     

相对冲击位置和补片层数对胶接修理CFRP复合材料层合板抗冲击性能的影响

本文针对碳纤维增强聚合物（CFRP）复合材料修补结构,基于连续损伤力学和粘结单元模型,在ABAQUS软件中对低速冲击载荷下不同冲击位置和补片层数的CFRP复合材料层合板内部和层间损伤进行了数值分析,并与试验结果进行了对比。选择相对冲击位置为0 mm、10 mm、20 mm、30 mm和40 mm时对应的五种修补结构,通过数值计算和试验,获得了修补结构在低速冲击过程中的冲击力、冲击能量等数据。在保持补片单层厚度不变的前提下,使补片层数从1层增加到5层,计算获得了修补结构的低速冲击响应。研究结果表明:冲头接触修补结构时会对补片造成较大的损伤,补片可以提高含孔损伤母板的抗冲击性能;冲击点离修补结构损伤孔越近,结构受冲击所产生的分层损伤越严重;增加补片的层数可以提高修补结构的抗冲击性能;通过对补片层数进行优化,得到优化层数为2,其对应的修补结构与无修补结构相比分层损伤面积减少了19.9%,较好地提升了母板的抗冲击性能。      

Design of optimum patch shape and size for bonded repair on damaged Carbon fibre reinforced polymer panels

Carbon fibre reinforced polymer (CFRP) composite laminates have become popular for structural applications as they are lighter, stronger and tougher. But they are also susceptible to damage while in service. Damage in composite structures reduces its structural integrity and hence the service life. For improved service life, the damages need to be repaired so that structural integrity is restored. Adhesively bonded composite patch repair is one of the prominent technique used for restoring the structural integrity of the damaged part. Patch shape is one of the important parameter in composite repair performance and it needs to be investigated thoroughly. In the present work, a 3D finite element based study is carried out to investigate the influence of various patch shapes on repair efficiency. Damaged CFRP laminates are repaired by symmetrical patch adhesively bonded over the damaged area. The panel analyzed is of pure unidirectional and quasi-isotropic laminate sequences. The patch shapes considered are circle, rectangle, square, ellipse, octagon and oval. Stress concentration factor (SCF) is estimated before and after the repair to evaluate their efficiency. Also peel stress is considered for quantitative comparison. The SCF reduction and peel stress are compared for various patch shapes keeping constant patch volume. Stress based 3D-Hashin’s failure criterion is employed for predicting the strength at damage initiation along with failure modes in notched and repaired panel. Optimal patch shape is then brought-out based on higher repair efficiency. Finally, a genetic algorithm based approach in-conjunction with finite element analysis is used for the optimization of patch geometry and adhesive thickness in order to obtain higher repair performance.     

复合材料补片加固含椭圆孔钢板刚度分析

针对复合材料补片加固损伤钢板的受力特点, 建立三维弹性力学模型, 对复合材料补片双面加固轴向受拉平板进行了应力和变形分析。研究了粘贴界面的剪应力分布规律, 钢板和补片内轴向拉力的分布规律, 分析了加固后平板相对加固前的相对刚度。研究了含椭圆孔钢板经复合材料补片加固后相对加固前以及相对完好钢板的刚度。结果表明, 复合材料胶接修补含孔钢板的刚度随着补片厚度的增加而增加, 且增强的趋势逐渐趋于缓和。当补片层数大于5层后, 单纯依靠增加补片的厚度并不能有效提高修复效果。解析法与有限元法的计算结果及试验结果吻合得比较好。      

复合材料层合板胶接贴补修理渐进损伤分析

建立了复合材料层合板胶接贴补修理构型渐进损伤分析的三维有限元模型, 其中层合板和胶层分别采用正交各向异性损伤和各向同性损伤的连续介质损伤力学模型, 整个分析过程中同时考虑层合板和胶层的损伤形成和扩展以及它们之间的相互影响, 单向压缩载荷作用下的层合板贴补修理构型的试验数据验证了该模型的有效性, 采用该模型分析了不同的贴补修理参数对修补强度的影响。 结果表明: 当层合板补片较薄时, 补片损伤是导致修补结构失效的主要原因; 当补片较厚时, 胶层失效是导致修补结构失效的主要原因, 此时补片厚度增加并不能显著增大修补结构的极限强度。在复合材料贴补修理时需要对补片和胶层进行详细优化设计。