Evaluation of Viscoelastic Characteristics of Short-fiber Reinforced Composite by Indentation Method

Indentation tests are performed to evaluate the viscoelastic characteristics of a short-fiber reinforced composite. Finite element analysis is also carried out to estimate the macroscopic viscoelastic characteristics of the composite by using a unit cell models. The results of indentation tests show that a force-displacement curve obtained by the indentation test depends on the area of the fibers appeared in the impression. The creep compliance evaluated by these indentation tests is compared to that by the finite element analysis. As the results, it is suggested that the result of indentation test performed on the surface of the composite without fibers means the measurement result for isotropic composite or anisotropic composite in the direction of the smallest rigidity. On the other hand, indentation test performed on the fiber indicates the measurement result of anisotropic composite in the direction of the largest rigidity. These results present the method to measure the macroscopic characteristics of short-fiber reinforced composite by indentation tests.     

An engineering analysis of penetration of metal ball into fibre-reinforced composite targets

An engineering analysis of computing the penetration problem of a steel ball penetrating into fibre-reinforced composite targets is presented. Assume the metal ball is a rigid body, and the composite target is a transversely isotropic elasto-plastic material. In the analysis, a spherical cavity dilatation model is incorporated in the cylindrical cavity penetration method. Simulation results based on the modified model are in good agreement with the results for 3-D Kevlar woven （3DKW） composite anti-penetration experiments. Effects of the target material parameters and impact parameters on the penetration problem are also studied.     

部分共同作用框架组合梁有限元分析模型

本文提出了一种新的适用框架整体分析的组合梁有限元模型。在分析了相互作用程度对组合梁刚度影响的基础上,根据Newmark等人的一维部分相互作用理论,建立起部分共同作用组合梁平衡微分方程;结合框架组合梁受力特点引入合理的边界条件,推导出了能够考虑滑移的组合梁单元弹性刚度方程;还给出了常见非节点荷载的等效荷载公式。该组合梁单元节点自由度少,每个构件只需一个单元来模拟,方便了带组合梁钢框架的结构分析。本文的研究还为进一步地考虑混凝土开裂、压碎,钢材屈服等非线性因素,建立组合梁单元弹塑性刚度矩阵提供了理论基础。     

钨纤维增强金属玻璃复合材料分段弹体侵彻性能研究

结合穿甲实验，基于复合材料细观有限元模拟，系统开展针对钨纤维增强金属玻璃复合材料分段弹体侵彻性能的研究，并与复合材料长杆弹进行对比分析。结果表明，相对于复合材料长杆弹显著的穿甲“自锐”行为和优异的侵彻性能，复合材料分段弹体在侵彻过程中的“自锐”特性有所减弱，且弹体结构容易发生分散，进而导致弹体侵彻能力明显降低。另外，分段数目和分段间隔等因素对复合材料分段弹体的侵彻性能具有一定影响，但总体而言，不同构型分段弹体的侵彻能力均弱于复合材料长杆弹。     

组合单元法在砂井地基有限元分析中的应用

针对砂井地基的平面应变有限元分析，本文首次将组合单元法引入到砂井地基的分析中，提出砂墙组合单元。该单元对常规等参元进行改进，在单元内部同时考虑砂井的涂抹作用和井阻作用，从而克服了常规有限元法在计算砂井地基时单元数和节点数过多的缺点。将砂墙组合单元加入USAP有限元计算软件，工程算例分析结果表明：与已有的各砂井地基的平面应变解答和荷兰的基础工程有限元分析软件PLAXIS相比，解答合理并有效地考虑砂井的涂抹作用和井阻作用；与常规有限元法相比，在保证计算精度的前提下，减少了可观的单元数和节点数，降低了计算的工作量。     

A moderate deflection composite helicopter rotor blade model with an improved cross-sectional analysis

The compatibility between a composite beam cross-sectional analysis based on the variational asymptotic approach, and a helicopter rotor blade model which is part of a comprehensive rotorcraft analysis code is examined. It was found that the finite element cross-sectional analysis code VABS can be combined with a moderate deflection rotor blade model in spite of the differences between the formulations. The new YF/VABS rotor blade model accounts for arbitrary cross-sectional warping, in-plane stresses, and moderate deflections. The YF/VABS composite rotor blade model was validated against experimental data and various rotor blade analyses by examining displacements and stresses under static loads, as well as aeroelastic stability of a composite rotor blade in hover, and forward flight vibratory hubloads of a four bladed composite rotor.     

损伤复合材料结构可靠性分析模型的初步探讨

大量实验研究表明,复合材料损伤容限设计主要是一个静力问题,基于此,本文用履盖的方法对局部损伤进行工程化处理,研究了固有损伤和冲击损伤对复合材料性能的影响;然后将这一处理方法引入到复合材料的可靠性分析中去,得到了带损伤的复合材料结构的可靠性分析模型,最后用两个算例检验了本文提出的方法,得出的结论与定性分析相同,对工程设计可以提供定量的指导。     

复合材料层合板粘弹性固化残余应力分析

基于Ｓｃｈａｐｅｒｙ积分型粘弹性本构关系，推导了考虑横向剪切效应的复合材料层合板线性热粘弹性有限元分析列式，对层合板的粘弹性响应和加工成型过程中的残余应力进行了分析，给出一些有意义的结果     

钢－混凝土组合梁非线性有限元分析

提出了部分剪力连接钢-混凝土组合梁非线性有限元分析的简化模型，该模型同时考虑了钢、混凝土材料的非线性本构关系和剪力连接件的滑移非线性对组合梁刚度和强度的影响，推导了考虑滑移的剪力连接件单元刚度矩阵。利用该模型计算了连续组合梁的极限荷载、挠度、应力以及滑移，与已有的理论计算结果和实验结果吻合，证明本方法分析钢-混凝土组合梁非线性的可靠性和实用性。     

含分层损伤复合材料层合板的压缩强度研究

给出了基于一阶剪切变形理论的含分层损伤层合板有限元分析模型,将含分层损伤层合板在压缩载荷作用下的强度破坏分析和屈曲破坏分析统一起来。先区分其破坏形式,然后再进行具体破坏分析,在屈曲特性分析中考虑了铺层强度破坏引起的刚度折减的影响,数值结果表明,该文给出的方法和结论对含分层损伤复合材料层合板的设计更具参考价值。     

考虑收缩徐变影响的新旧混凝土叠合梁非线性分析实用方法

界面存在粘结滑移的新旧混凝土叠合梁是一种重要的工程梁.以叠合面上的变形协调条件为计算条件,推导出叠合梁以轴力表达的非线性微分方程.求解该微分方程,得到截面协同工作系数理论表达式.通过该截面协同工作系数,建立了能够准确反映新旧混凝土叠合梁承载力与变形的非线性实用分析方法,使得Bernoulli假定与截面协同工作系数达到了统一,并与已有解析解进行了对比分析,发现计算精度满足工程需求,说明了该分析方法的实用性.     

Analysis of frequency-domain vibration response of thin plate attached with viscoelastic free layer damping

To predict the vibration response of viscoelastic composite structure, two key issues need to be conducted, one is introducing the constitutive model of viscoelastic material into the analysis model and the other is describing the real damping behavior of viscoelastic composite structure. The emphasis of this study is to obtain the effects of frequency dependence on the vibration response of viscoelastic composite structure and the method of introducing two kinds of damping (viscoelastic material damping and remaining equivalent viscous damping). Vibration response analysis in frequency domain was investigated for viscoelastically damped plate. A cantilever plate attached with the ZN_1 viscoelastic free layer damping (FLD) was chosen to demonstrate the developed method. Frequency-domain response of the composite plate were solved and the obtained results were compared with the experimental values for the purpose of assessing the rationality of the proposed method. In addition, in order to obtain the effects of viscoelastic material parameters on vibration response of viscoelastic composite structure, a detailed parametric analysis was performed. This study shows that the frequency dependent characteristic of viscoelastic material has significant influence on the vibration response in the resonant region and acceptable results can be achieved in the non-resonant region if frequency dependent parameters are substituted by average values of the viscoelastic parameters reasonably in the analysis process.     

The effect of transverse shear deformation on the buckling of two-layer composite columns with interlayer slip

This paper presents an efficient mathematical model for studying the buckling behavior of geometrically perfect elastic two-layer composite columns with interlayer slip between the layers. The present analytical model is based on the linearized stability theory and is capable of predicting exact critical buckling loads. Based on the parametric analysis, the critical buckling loads are compared to those in the literature. It is shown that the discrepancy between the different methods can be up to approximately 22%. In addition, a combined and an individual effect of pre-buckling shortening and transverse shear deformation on the critical buckling loads is studied in detail. A comprehensive parametric analysis reveals that generally the effect of pre-buckling shortening can be neglected, while, on the other hand, the effect of transverse shear deformation can be significant. This effect can be up to 20% for timber composite columns, 40% for composite columns very flexible in shear (pyrolytic graphite), while for metal composite columns it is insignificant.     

BRIDGE-TOUGHENING ANALYSIS OF THE FIBER REINFORCED COMPOSITE CONTAINING INTERPHASE EFFECT

A detailed fracture mechanics analysis of bridge-toughening in a fiberreinforced composite is presented in this paper.The integral equation governing bridge-toughening as well as crack opening displacement (COD) for the composite withinterfacial layer is derived from the Castigliano's theorem and interface shear-lagmodel.A numerical result of the COD equation is obtained using the iteration solutionof the second Fredholm integral equation.In order to investigate the effect of variousparameters on the toughening,an approximate analytical solution of the equation ispresent and its error analysis is performed,which demonstrates the approximatesolution to be appropriate.A parametric study of the influence of the crack length,interracial shear modules,thickness of the interphase,fiber radius,fiber volumefraction and properties of materials on composite toughening is therefore carried out.The results are useful for experimental demonstration and toughening design includingthe fabrication process of the composite.     

冰载荷下不锈钢复合板挠度特性分析

以复合板中面的挠度响应作为不锈钢复合板抗冲击性能的评价指标,基于能量法和经典层合板理论,考虑层间结构参数设计,通过横向载荷下的弯曲平衡微分方程,建立冰载荷下不锈钢复合板挠度响应简化解析模型。该分析模型将整个动态响应分析过程分为冰载荷计算分析和动力学方程求解两个阶段。分析了冰载荷模型的面倾角、冲击速度和碰撞位置对冰载荷的影响,确定极端工况参数,汇总接触面的节点力数据;分析了层厚比对挠度响应的影响规律;基于LS-DYNA有限元仿真以及数值算例分析,对比挠度响应仿真结果和解析计算值,验证了本文简化解析模型的准确性,研究结果对不锈钢复合板抗冲击性能分析和评估具有一定的参考价值。     

Introducing Heterogeneity into the Micro-Scratch Test Fracture Toughness Relation for Brittle Particle Composites

Existing analysis methods of scratch test data are limited in their application to composite materials since they are built on the assumption of homogeneous material. In this study, the heterogeneity of the composite material is considered for analysis of scratch data on a resin and glass bead particle composite. Experiments are conducted using two approaches: macroscale three-point single edge notch and micro-scratch. An analysis method is presented which introduces a region in front of the crack tip to calculate the energy release rate during the fracture process which accounts for the heterogeneity of this region. By comparing with the experimental results, it is observed that this analysis method reduces the difference in fracture toughness derived from macroscale and microscale tests, and matches the trend of fracture toughness values as a function of particle volume fraction. This observation provides the insight that the local microstructure of the material needs to be considered in the scratch test analysis of particle composites.     

具有叉指式电极的1-3型压电复合材料层合板力电耦合行为的三维精确分析

基于三维弹性理论和压电理论,导出了含有1-3型压电复合材料层的有限长矩形层合简支板的静力平衡方程和边界条件,给出了该层合板在叉指式电极和外力共同作用下力电耦合特性的三维精确解.数值算例的计算结果与有限元解进行了对比,取得了很好的一致性.研究了压电矩阵各向异性和刚度矩阵各向异性以及电势等因素对其挠曲面扭率最大值的影响.数值结果表明层合板扭率最大值的绝对值随压电矩阵各向异性系数Rd的增大而增大并随刚度矩阵各向异性系数Rc的减小而增加.     

复合材料弹塑性多尺度分析模型与算法

对材料非线性多尺度分析的计算模型与算法进行研究.在构建周期分布单胞分析算法的基础上,发展针对复合材料结构材料非线性多尺度分析的一般有限元方法.方法的特点是将所建立的单胞分析过程作为有限元分析的子程序嵌入到总程序系统当中,完成对应的高斯点应力计算,因而使所发展的方法具有实现方便的特点.给出数值计算结果,验证了方法与所发展的多尺度有限元分析程序的正确与有效性.     

大开口复合材料层合板强度破坏研究

复合材料层合板的各向异性及非均质,使得复合材料层合板内部的破坏形式非常复杂.在复合材料结构的设计中,为满足制造及使用功能上的需求,在复合材料层合板承力结构件上不可避免地需要设计各种开口.然而,含大开口复合材料层合板的强度破坏问题变得更为复杂,使得现有的强度理论面临新的挑战.针对碳纤维增强复合材料大开口层合板受单向拉伸载荷作用下的强度破坏问题进行了数值分析和实验研究.首先,根据Hashin准则和刚度退化模型,对含不同圆形开口尺寸的[0]_(10)单向铺层、[0/90]_5和[±45]_5正交铺层的层合板,进行了单向拉伸载荷作用下渐进失效的数值模拟分析,获得了对应结构的极限载荷和破坏模式.在此基础上,采用数字图像相关方法,进行复合材料大开口层合板强度破坏的实验研究.研究结果表明,大开口复合材料层合板在单向拉伸加载下主要呈现脆性破坏形式,破坏起始位置处于应力集中区.此外,破坏强度和失效模式与复合材料铺层方式和开口尺寸大小密切相关.其中[±45]_5铺层的开口层合板承载能力最弱,分层破坏最严重.开口尺寸越大,结构的极限载荷值越低.同实验测试结果相比,数值模拟对复合材料层合板的损伤失效分析略显不足,往往很难全面分析复合材料层合板破坏失效过程中的各种因素的影响.     

The effect of fiber damage on the longitudinal creep of a CFMMC

Fiber failures which may exist in a continuous fiber composite before the composite is loaded or generated while the composite is loaded, introduce an additional strain component not included in existing continuous fiber models. Equations are developed which can be used to calculate the magnitude of this additional strain. A Finite Element Model (FEM), in the form of a Representative Volume Element (RVE), calculates the stress field surrounding a fiber break. Statistical analysis is used to infer the behavior of a large composite sample from the stress analysis of a single break. The creep strain, the time to failure, and time-dependent composite strength can all be calculated by combining the FEM results, the statistical analysis model, and knowledge of the initial average fiber length. Important variables included in the calculation are process-related parameters such as the fiber-matrix interface strength and roughness.