湿热环境下含分层平面编织玻璃纤维/环氧树脂基复合材料层合板振动特性

通过理论推导与有限元仿真,研究了湿热环境下一端固支与四端固支约束含分层平面编织玻璃纤维/环氧树脂基复合材料层合板的不同分层夹角及分层位置的振动特性。首先基于Mindlin一阶剪切变形理论与Hamilton原理,考虑湿热应力和质量效应,依据湿度与温度的等效性,推导了受湿热环境影响的含分层层合板的湿热本构方程与固有频率表达式。利用有限元软件ABAQUS自带的用户材料子程序（UMAT）接口,编制相应的接口程序,建立了一系列温湿度组合下的分层损伤模型。并将数值结果与文献中试验值进行了验证。算例结果表明:湿热效应下,分层加剧了湿热环境下平面编织层合板各阶固有频率的下降;不同的分层夹角会引起固有频率值的改变,夹角越大固有频率下降幅值越大;湿度对分层层合板振动特性的影响比温度对分层层合板振动特性的影响显著;湿热效应会引起高阶频率向低阶的漂移,加剧局部共振现象;表面分层与中面分层都会引起各阶固有频率值下降,但下降幅值两者之间差别不大。      

湿-热-力耦合环境下复合材料结构损伤分析与性能研究

将考虑湿热效应的经典层合板理论引入有限元方法中, 通过精确考察单层板等效参数衰减、追踪初始破坏后的卸载以及对最终破坏进行判定, 在精确预测湿热环境对复合材料性能影响的同时追踪了损伤演化过程。通过建立湿-热-力耦合下复合材料宏观性能的定量表达式, 发展湿-热-力耦合环境下复合材料性能演化表征与预测方法, 实现在有限元分析中考虑湿热效应的影响。对3 种不同铺层方式复合材料层合板进行湿热环境试验研究, 并利用本文中分析方法进行损伤模拟, 分析结果与实验结果符合得较好。      

循环湿热环境下碳纤维复合材料界面性能

为研究循环湿热环境对CCF300/5405复合材料体系界面性能的影响,首先对该体系循环吸湿—脱湿行为进行研究,其次分析湿热环境下层间剪切强度的变化,最后采用扫描电镜观察纤维/基体界面的微观形貌.研究结果表明:CCF300/5405体系吸湿处理后,纤维与基体间界面遭到水分破坏,产生大量空隙和裂纹,使得水分的扩散速率明显增加,吸湿率增大,且这种破坏不可逆;吸湿之后材料层间剪切强度下降,烘干之后可以恢复到近于自然干态水平;相对于水分对复合材料的不可逆破坏,可逆破坏对层间剪切强度值减小的贡献更大.     

湿热环境对旋转复合材料梁摆振特性的影响

首先,基于复合材料在湿热环境下的本构关系推导了旋转复合材料梁轴力和弯矩的表达式,分析了温度和湿度对轴力和弯矩的影响,然后,基于d’Alembert原理建立了旋转复合材料梁摆振控制方程,并应用Galerkin法进行求解,分析了温度和湿度对旋转复合材料梁刚度的影响,最后,通过数值模拟讨论了湿热环境对旋转复合材料梁摆振动力学特性的影响。结果表明:湿热环境对旋转复合材料梁的摆振频率和模态影响显著,摆振频率随湿热环境加剧而降低,热膨胀效应对摆振频率的影响大于材料性能变化对其的影响,湿热环境与旋转的联合作用使模态的节点位置发生明显偏移。     

湿热环境下含分层平面编织玻璃纤维/环氧树脂基复合材料层合板振动特性

该文研究了玻璃纤维编织复合材料制成的可收卷层板在大变形条件下的弯曲静力性能和疲劳性能。通过弯曲静力试验得到了试验件在大变形条件下的应变和位移的关系;通过有限元模拟静力试验并与试验结果对照,确定了疲劳试验的载荷;研究了在大变形条件下不同铺层层板的弯曲疲劳寿命及失效模式和相同铺层层板的疲劳寿命曲线。结果表明：复合材料层板在大变形弯曲时具有明显的非线性行为,且(±45°)铺层层板弯曲疲劳性能明显优于(0°/90°)铺层层板;在最小应变和最大应变比不变的情况下,相同铺层层板的弯曲最大应变和对数疲劳寿命之间存在线性关系。     

不同湿热条件下碳纤维/环氧复合材料湿热性能实验研究

对比研究了环氧5228A树脂及碳纤维/环氧5228A树脂复合材料层合板在3种湿热环境(水煮、70℃水浸,70℃85%相对湿度)下的湿热性能,考察了湿热条件对复合材料层间剪切性能的影响规律,并从吸湿特性、物理化学特性、树脂力学性能、湿应力等方面分析了不同湿热环境下复合材料性能衰减的机制。研究表明,碳纤维/高温固化环氧树脂复合材料层间剪切性能主要是由吸湿率决定,相同吸湿率不同湿热条件下性能的下降幅度基本相同;3种湿热条件下该树脂及其复合材料未发生化学反应、微裂纹等不可逆变化,复合材料层合板湿热老化机制主要是吸入水分后基体增塑和树脂、纤维湿应变不一致导致的湿应力对复合材料性能的负面作用。     

全湿热场下碳纤维/环氧树脂复合材料弯曲性能及寿命预测

以碳纤维/环氧树脂（T700/TR1219B）复合材料为研究对象,采用湿度场和温度场单一及耦合的方式,研究了不同湿热环境下其弯曲性能的变化,通过断口形貌和表面粗糙度表征,分析其湿热损伤机制。结果表明:T700/TR1219B复合材料的弯曲性能受湿度场和温度场影响明显,当吸湿率达到2%时,弯曲强度从干态的1 440.60 MPa下降到1 081.07 MPa;随温度的升高弯曲性能呈下降趋势,且在玻璃化转变温度T_g所在温度区间发生陡降,当环境温度为180℃时,弯曲模量和弯曲强度分别下降了71.18%和93.32%;高温高湿环境下弯曲性能陡降的温度区间前移,且性能衰减并非单一湿度场和温度场下衰减量的简单叠加。通过微观形貌分析发现,湿度场主要导致树脂水解脱黏,温度场下树脂形态破坏严重,而湿热耦合场对纤维与树脂均产生较大程度的损伤。考虑湿度场和温度及湿热耦合相关项,建立并验证了全湿热场下剩余弯曲强度模型,结合湿热老化时间、环境当量等参数提出T700/TR1219B复合材料的寿命预测模型。      

Formulation of reference surface element and its applications in dynamic analysis of delaminated composite beams

This paper presents a new finite element formulation, referred to as reference surface element (RSE) model, for numerical prediction of dynamic behaviour of delaminated composite beams and plates using the finite element method. The RSE formulation can be readily incorporated into all elements based on the Timoshenko beam theory and the Reissner–Mindlin plate theory taking into account the transverse shear deformations. The ‘free model' and ‘constrained model' for dynamic analysis of delaminated composite beams and/or plates have been unified in this RSE formulation. The RSE formulation has been applied to an existing 2-node Timoshenko beam element taking into account the transverse shear deformations and the bending–extension coupling. Frequencies and vibration mode shapes are determined through solving an eigenvalue problem. Numerical results show that the present RSE model is reliable and practical when used to predict frequencies and mode shapes of delaminated composite beams. The RSE formulation has also been used to investigate the effects of the number, size and interfacial loci of delaminations on frequencies and mode shapes of composite beams.     

Adhesive element modelling and weighted static shape control of composite plates with piezoelectric actuator patches

A novel finite element model is presented for static and dynamic analysis of composite plates integrated with a laminated piezoelectric layer, a host laminated composite plate and an adhesive layer between them. A new adhesive element is developed which includes both peel and shear effects in the adhesive layer based on first‐order shear deformation plate theory. The thin adhesive layer between the piezoelectric layer and the host plate is modelled by assuming that it carries constant shear and peel strains throughout its thickness. In addition, a weighted static shape control scheme for finding the optimal voltage distribution for static shape control is given. By selecting different weighting matrices, a variety of items such as displacements, slopes, curvatures, strains and even generalized forces, can be included in finding the optimal actuating voltage for static shape control. The present model is validated by comparing with those results available in the literature. The numerical results show that the weighted linear least method can give a satisfactory voltage distribution to best match the desired shape. Copyright © 2004 John Wiley & Sons, Ltd.     

A FEM model for the active control of curved FGM shells using piezoelectric sensor/actuator layers

In this paper, a generic finite element formulation is developed for the static and dynamic control of FGM (functionally graded material) shells with piezoelectric sensor and actuator layers. The properties of the FGM shell are graded in the thickness direction according to a volume fraction power‐law distribution. The proposed finite element model is based on variational principle and linear piezoelectricity theory. A constant displacement and velocity feedback control algorithm coupling the direct and inverse piezoelectric effects is applied in a closed‐loop system to provide feedback control of the integrated FGM shell structure. Both static and dynamic control of FGM shells are simulated to demonstrate the effectiveness of the proposed active control scheme within a framework of finite element discretization and piezoelectric integration. Copyright © 2002 John Wiley & Sons, Ltd.     

T800H碳纤维表面特性及T800H/BA9918复合材料湿热性能研究

为了研究T800H碳纤维的表面特性及其与BA9918树脂的界面匹配性,分别采用SEM、AFM、XPS和TGA对T800H碳纤维表面形貌、表面化学特性以及碳纤维上浆剂热稳定性进行表征,测试了T800H/BA9918复合材料湿热处理前后0°压缩强度、90°拉伸强度和层间剪切强度,并得到了其在湿热处理前后的开孔压缩和冲击后压缩性能.测试发现T800H碳纤维表面有明显的沟槽,有利于表面机械啮合作用;T800H/BA9918复合材料经29 J能量冲击后压缩强度为314 MPa;在130℃湿态环境下其0°压缩强度和层间剪切强度保持率高于58%,开孔压缩强度保持率高于60%.试验结果证明T800H碳纤维与BA9918树脂具有良好的界面匹配性,T800H/BA9918复合材料具有优异的耐湿热性能.     

Integration of active vibration control methods with finite element models of smart laminated composite structures

Vibration control problems can be directly and systematically solved in a single analysis stage using commercial finite element programs. Integration of control methods into the finite element solutions (ICFES) can be achieved in ANSYS. In this work, first, the direct velocity feedback (DVF) control is tested on a 3-DOF mechanical system under a step input. The simulation results obtained by the ICFES are compared with the analytical results obtained by the Laplace transform method. Then, active control of free and forced vibrations in a smart laminated composite structure (SLCS) with two different lay-ups is studied numerically and experimentally. The SLCS consists of a symmetric laminated glass–epoxy composite beam with [0/90]_s and [45/−45]_s lay-ups and a piezoelectric actuator. For the vibration suppression, the DVF control tested on a mechanical system is applied to the SLCS. In addition, displacement feedback (DF) control is studied. Experiments are conducted to verify the natural frequencies and the closed loop time responses. Analytical results for the mechanical system and experimental results for the SLCS match well to the corresponding results obtained using the ICFES technique.     

Failure analysis of multiple delaminated composite plates due to bending and impact

The present work aims at the first ply failure analysis of laminated composite plates with arbitrarily located multiple delaminations subjected to transverse static load as well as impact. The theoretical formulation is based on a simple multiple delamination model. Conventional first order shear deformation is assumed using eight-noded isoparametric quadratic elements to develop the finite element analysis procedure. Composite plates are assumed to contain both single and multiple delaminations. For the case of impact, Newmark time integration algorithm is employed for solving the time dependent multiple equations of the plate and the impactor. Tsai-Wu failure criterion is used to check for failure of the laminate for both the cases. To investigate the first ply failure, parametric studies are made for different cases by varying the size and number of delaminations as well as the stacking sequences and boundary conditions.     

复合材料夹层板屈曲强度的分散性分析

将面板单层及芯层厚度、 面板纤维方向角和材料参数作为随机变量, 通过编制基于高阶剪切理论的随机有限元程序, 对复合材料夹层板的屈曲强度分散性进行了分析, 得到了不同铺层方式下夹层板屈曲强度分散系数随纤维方向角及夹层板长厚比的变化规律。并通过对屈曲强度的分散系数进行灵敏度分析, 确定了影响分散系数大小的主要因素, 从而为材料设计、 制造工艺改进和夹层板结构可靠度的提高提供了理论依据。      

湿热环境下Carbon/Epoxy复合材料层合板动态压缩性能

随着纤维增强复合材料的广泛应用, 研究其在湿热环境下的动态力学性能具有重要的理论研究意义与工程应用价值。首先对碳纤维增强环氧树脂基(Carbon/Epoxy)复合材料层合板试件进行了湿热处理, 其后采用分离式霍普金森压杆(SHPB)技术开展了干/湿态试件高应变率压缩实验并对实验结果进行分析。结果表明: 材料脱(吸)湿过程呈现出两段式特点, 存在二次脱(吸)水现象; Carbon/Epoxy复合材料层合板的强度在垂直铺层方向具有显著的应变率敏感性, 随着应变率从1 500 s-1增加至6 000 s-1, 其强度增加近3倍, 与此同时应变率对其弹性模量的影响却非常微弱; 此外, 湿热处理有助于提升该材料的动态力学性能, 经20 d吸湿后材料动态强度有最大12.45%的增幅, 吸湿使得材料动态强度的上升在应变率较低时比较明显。      

Finite volume analysis of laminated composite plates

A numerical procedure for analysis of general laminated plates under transverse load is developed utilizing the Mindlin plate theory, the finite volume discretization, and a segregated solution algorithm. The force and moment balance equations with the laminate constitutive relations are written in the form of a generic transport equation. In order to obtain discrete counterparts of the governing equations, the plate is subdivided into N control volumes by a Cartesian numerical mesh. As a result, five sets of N linear equations with N unknowns are obtained and solved using the conjugate gradient method with preconditioning. For the method validation, a number of test cases are designed to cover thick and thin laminated plates with aspect ratio (width to thickness) from 4 to 100. Simply supported orthotropic, symmetric cross‐ply, and angle‐ply laminated plates under uniform and sinusoidal pressure loads are solved, and results are compared with available analytical solutions. The shear correction factor of 5/6 is utilized throughout the procedure, which is consistent with test cases used in the reviewed literature. Comparisons of the finite volume method results for maximum deflections at the center of the plate and the Navier solutions obtained for aspect ratios 10, 20, and 100 shows a very good agreement. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermal postbuckling analysis of laminated composite plates

The thermal postbuckling behavior of graphite/epoxy multi-layered rectangular plates of various boundary conditions is studied using the finite element method. Temperature dependent thermal and elastic properties of the material are used in the analysis. The nonlinear finite element equations are solved as a sequence of linear eigenvalue problems to trace the thermal postbuckling paths of 15-layered symmetric angle-ply plates. The presence of secondary instability with an unsymmetric deformation mode has been identified for symmetric laminates under uniform temperature rise. In the case of linearly varying temperature rise through the thickness of the plate, the nonlinear equilibrium equations are solved by the modified Newton–Raphson technique to get the temperature-displacement curves.     

Stochastic progressive failure analysis of laminated composite plates using Puck's failure criteria

The present work deals with second-order statistics of the progressive failure response of laminated composite plates subjected to in-plane uniaxial and bi-axial loadings with random system properties. A stochastic finite element method based on higher-order shear deformation theory combined with first- and second-order perturbation technique is used for solution of random progressive failure equation. A Puck failure criterion is used for the evaluation of first ply and last-ply failure load. The results obtained using the present solution approach are validated with the results available in the literature and Monte Carlo simulation.     

Multiscale analysis of laminated plates with integrated piezoelectric fiber composite actuators

This study is concerned with the detailed analysis of fiber-reinforced composite plates with integrated piezoceramic fiber composite actuators. A multiscale framework based on the asymptotic expansion homogenization method is used to couple the microscale and macroscale field variables. The microscale fluctuations in the mechanical displacement and electric potential are related to the macroscale deformation and electric fields through 36 distinct characteristic functions. The local mechanical and charge equilibrium equations yield a system of partial differential equations for the characteristic functions that are solved using the finite element method. The homogenized electroelastic properties of a representative material element are computed using the characteristic functions and the material properties of the fiber and matrix. The three-dimensional macroscopic equilibrium equations for a laminated piezoelectric plate are solved analytically using the Eshelby-Stroh formalism. The formulation admits different boundary conditions at the edges and is applicable to thick and thin laminated plates. The microscale stresses and electric displacement in the fibers and matrix are computed from the macroscale fields through interscale transfer operators. The multiscale analysis procedure is illustrated using two model problems. In the first model problem, a simply-supported sandwich plate consisting of a piezoceramic fiber composite shear actuator embedded between two graphite/polymer layers is studied. The second model problem concerns a cantilever graphite/polymer substrate with segmented piezoceramic fiber composite extension actuators attached to its top and bottom surfaces. Results are presented for the homogenized material properties, macroscale deformation, macroscale average stresses and microscale stress distributions.     

电子探针在有源光纤定量分析中的应用

为给有源光纤的工艺开发和性能研究提供有力支撑,该文利用场发射型电子探针EPMA-8050G对光纤纤芯的元素掺杂微区进行系统的定性定量分析,进一步研究石英基质的测试特点以及测试条件对样品烧蚀的影响.能谱仪(EDS)和波谱仪(WDS)的定性分析结果表明,分析含量较低的元素如稀土元素Yb和轻元素F时,WDS有明显的优势.状态...