含脱层损伤复合材料层合梁冲击动力响应实验研究

对纤维增强复合材料层合梁在受轴向冲击时的动力响应问题进行了实验研究。实验以单向玻璃纤维布和环氧树脂材料制作试件,在层间预埋薄铜箔模拟脱层损伤。采用激光测速仪测量子弹速度,动态应变仪和TDS420A数字示波器记录应变时程曲线进行动力响应分析。实验结果表明铺层角度是决定材料性能的主要原因,脱层损伤的存在及大小对动力响应和发生动力屈曲有重要影响。此外,初始缺陷的影响也是不可忽视的重要因素。     

含初缺陷裂纹损伤梁的冲击动力屈曲

由Hamilton原理导出考虑初始缺陷及横向剪切变形时裂纹梁的动力屈曲控制方程;应用断裂力学中常用的线弹簧模型将裂纹引入到屈曲控制方程中;基于B-R动力屈曲判断准则,采用数值方法求解了受轴向冲击载荷作用时裂纹梁的动力屈曲;对比讨论了不同冲击速度、初始几何缺陷大小以及分布形式等因素对梁冲击动力屈曲的影响。     

爆炸冲击下复合材料层合扁球壳的动力屈曲

研究计及横向剪切的复合材料层合扁球壳在爆炸冲击载荷作用下的非线性轴对称动力屈曲问题。通过在复合材料层合扁球壳非线性稳定性的基本方程中增加横向转动惯量项并引入R.H.Cole理论的爆炸冲击力,得到爆炸冲击下复合材料层合扁球壳的动力控制方程,应用Galerkin方法得到用顶点挠度表达的爆炸冲击动力响应方程,并采用Runge-Kutta方法进行数值求解,采用Budiansky-Roth准则确定冲击屈曲的临界载荷,讨论了壳体几何尺寸对复合材料层合扁球壳冲击屈曲的影响;数值算例表明,此方法是可行的。     

复合材料脱层梁的屈曲分析

本文研究了具有任意位置透型脱层的复合材料梁的屈曲问题。基于弹性理论建立了复合材料脱层梁的基本方程式。对脱层梁进行了分区处理,利用B样条函数作为位移型函数的基函数,方便地描述了脱层长度、脱层位置。考虑边界条件、区间位移连续性条件和弯矩剪力的平衡条件以及纵向内力的附加条件,对基本方程式进行了求解。得出了脱层位置不同,脱层长度不同的屈曲荷载的变化规律,并与轴对称脱层时的屈曲荷载进行了比较,认为层合梁考虑脱层对屈曲的影响是非常必要的。     

脱层梁屈曲的高阶剪切理论

脱层的存在将会大大降低层合结构的屈曲载荷。该文将含任意位置脱层的两端固支梁分成多段子层,用厚度的三次多项式模拟脱层梁屈曲时子层的轴向位移,利用变分原理和欧拉方程导出了脱层梁的屈曲方程和定解条件,并用状态空间方法进行求解。通过与一阶剪切理论和经典理论的比较,指出了它们各自的适用范围;考虑了脱层梁三种不同的屈曲模态。分析了脱层长度、深度、位置和材料的铺层方向对脱层梁屈曲载荷的影响;最后给出了多处简单脱层的屈曲分析。     

矩形脉冲作用下复合材料层合扁球壳的冲击屈曲分析

研究了计及横向剪切的复合材料层合扁球壳在矩形脉冲载荷作用下的非线性动力屈曲问题;采用Galerkin方法得到以顶点挠度表达的动力响应方程,并用Runge-Kutta方法进行数值求解,应用Budiansky-Roth准则(简称B-R准则)确定冲击屈曲的临界荷载;讨论了壳体几何尺寸和物理参数对复合材料层合扁球壳冲击屈曲的影响;数值算例表明,该方法是可行的.     

湿热条件下具脱层压电层合梁的后屈曲及脱层扩展分析

考虑湿热条件、横向剪切变形、几何非线性和压电效应的影响,建立具脱层压电层合梁的本构关系和非线性平衡微分方程,采用有限差分法和迭代法对问题进行求解;在此基础上.应用Griffith准则,导出了脱层前缘处的能量释放率表达式,讨论了不同因素对压电层合梁后屈曲性能和脱层扩展的影响.     

复合材料结构的动力屈曲研究进展

本文系统地回顾了复合材料结构的动力屈曲研究进展，对周期性动载荷和瞬态动载荷作用下，复合材料结构的动力屈曲作了阐述；讨论了耦合效应，横向剪切变形、初始几何缺陷以及铺层方式等因素对动力屈曲的影响；就复合材料结构动力屈曲研究的发展前景提出了一些有益的建议     

具脱层的正交铺设圆柱壳的初始后屈曲分析

基于非线性弹性理论,建立了含脱层正交铺设圆柱壳的后屈曲控制方程,应用Koiter初始后屈曲理论和小参数摄动法,导出了系统的一阶和二阶摄动控制方程,以及相应的边界条件、位移连续条件和力平衡条件,然后逐阶求解．算例中,讨论了不同脱层深度和长度对脱层复合材料圆柱壳屈曲和初始后屈曲特性的影响,并与已有文献进行了比较．     

具有分层损伤的不同加筋形式复合材料层合板的后屈曲性态研究

基于板的一阶剪切理论和V on-K arm an大挠度理论,分别推导了复合材料层合板和层合梁的几何非线性有限元列式,提出了含嵌入分层的复合材料加筋层合板在受压缩载荷作用下的后屈曲有限元分析方法,对在板厚方向具有不同分层位置的加筋板结构进行了有限元数值分析,研究了不同的加筋方式及筋的分布对具有分层损伤的复合材料加筋层合板的后屈曲性态的影响,所得结果对确定在压缩载荷作用下含损伤复合材料加筋层合板的剩余承载能力具有参考价值。     

Buckling and Postbuckling of Laminated Thin Cylindrical Shells under Hygrothermal Environments

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Thermomechanical postbuckling of composite laminated cylindrical shells with local geometric imperfections

The effect of local geometric imperfections on the buckling and postbuckling of composite laminated cylindrical shells subjected to combined axial compression and uniform temperature loading was investigated. The two cases of compressive postbuckling of initially heated shells and of thermal postbuckling of initially compressed shells are considered. The formulations are based on a boundary layer theory of shell buckling, which includes the effects of the nonlinear prebuckling deformation, the nonlinear large deflection in the postbuckling range and the initial geometric imperfection of the shell. The analysis uses a singular perturbation technique to determine buckling loads and postbuckling equilibrium paths. Numerical examples are presented that relate to the performances of cross-ply laminated cylindrical shells with or without initial local imperfections, from which results for isotropic cylindrical shells follow as a limiting case. Typical results are presented in dimensionless graphical form for different parameters and loading conditions.     

Nonlinear buckling optimization of composite structures considering “worst” shape imperfections

Nonlinear buckling optimization is introduced as a method for doing laminate optimization on generalized composite shell structures exhibiting nonlinear behaviour where the objective is to maximize the buckling load. The method is based on geometrically nonlinear analyses and uses gradient information of the nonlinear buckling load in combination with mathematical programming to solve the problem. Thin-walled optimal laminated structures may have risk of a relatively high sensitivity to geometric imperfections. This is investigated by the concepts of “worst” imperfections and an optimization method to determine the “worst” shape imperfections is presented where the objective is to minimize the buckling load subject to imperfection amplitude constraints. The ability of the nonlinear buckling optimization formulation to solve the laminate problem and determine the “worst” shape imperfections is illustrated by several numerical examples of composite laminated structures and the application of both formulations gives useful insight into the interaction between laminate design and geometric imperfections.     

含初缺陷复合材料圆柱曲板的动力屈曲分析

基于修正的一阶剪切变形理论，利用Ｈａｍｉｌｔｏｎ原理导出包含横向剪切变形和转动惯量的复合材料长圆柱曲板的非线性动力方程，通过将位移和载荷展开为Ｆｏｕｒｉｅｒ级数，把非线性偏微分方程组转化为二阶常微分方程组，并可由四阶Ｒｕｎｇｅ－Ｋｕｔｔａ方法数值求解，通过算例，讨论了有关因素对迭层复合材料圆柱曲板动力屈曲的影响。     

Postbuckling of pressure-loaded shear deformable laminated cylindrical panels

IntroductionInrecentyears,fiber_reinforcedcompositelaminatedpanelshavebeenwidelyusedintheaerospace,marine ,automobileandotherengineeringindustries .Theproblemofbucklingandpostbucklingofcylindricalpanelsunderaxialcompressionortorsionhasbeenextensivelystudied .Incontrast,theliteratureoncylindricalpanelsunderpressureloadingisrelativelyspares.Thesestudiesincludealinearbucklinganalysis (Singeretal.[1]) ,anonlinearbucklinganalysi(YamadaandCroll[2 ]) ,anelastoplasticbucklinganalysisusingreducedstif…     

Free vibration analyses of axially loaded laminated composite beams based on higher-order shear deformation theory

The dynamic stiffness matrix method is introduced to solve exactly the free vibration and buckling problems of axially loaded laminated composite beams with arbitrary lay-ups. The Poisson effect, axial force, extensional deformation, shear deformation and rotary inertia are included in the mathematical formulation. The exact dynamic stiffness matrix is derived from the analytical solutions of the governing differential equations of the composite beams based on third-order shear deformation beam theory. The application of the present method is illustrated by two numerical examples, in which the effects of axial force and boundary condition on the natural frequencies, mode shapes and buckling loads are examined. Comparison of the current results to the existing solutions in the literature demonstrates the accuracy and effectiveness of the present method.