【作者】 李志敏；

【导师】 沈惠申；

【作者基本信息】 上海交通大学 ， 船舶与海洋结构物设计制造， 2008， 博士

【摘要】 纤维增强和编织复合材料是由基体和高性能的纤维材料根据实际需要组合而成的两种复合材料,具有比强度高、比刚度大、易成型、易修补、材料性能可以设计等一系列优点,适宜制造结构复杂的船型,可缩短建造周期,复合材料船艇的维护费用也低于钢船和木船。圆柱壳结构是复合材料实际应用中最为常见的结构形式之一,比如海洋平台的立管、输水输油管道、贮液罐、潜器、高速舰艇的推进器及鱼雷的外壳等等。近几年,无论在复合材料及其结构的设计、制造和应用领域,还是在复合材料及其结构力学问题的理论研究方面,国内外发展迅速,取得很大进展。随着制造工艺的改进,复合材料的各项性能指标不断提高,许多工程结构中的主要受力构件已由复合材料制造,这些结构在使用过程中,有可能受到外部机械载荷的作用发生屈曲而出现承载能力下降甚至破坏的情况,因此复合材料结构的屈曲问题一直受到国内外学者的关注。为了更加深入了解圆柱壳结构的屈曲和后屈曲特性,更好地发挥其在船舶和海洋工程结构中的作用,我们有必要应用边界层理论对中等厚度的纤维增强和编织复合材料剪切圆柱壳的屈曲和后屈曲特性进行研究。本文的研究工作主要包括:将壳体屈曲的边界层理论推广运用到纤维增强各向异性层合剪切圆柱壳。分析中同时考虑前屈曲非线性变形,后屈曲大挠度和初始几何缺陷的影响以及横向剪切变形和耦合刚度的影响,采用奇异摄动方法给出完全各向异性层合圆柱剪切壳在轴压、外压和扭矩作用下的既满足控制方程又在渐近意义上严格满足边界条件的后屈曲大挠度渐近解。通过对屈曲与后屈曲等一系列问题的求解和分析揭示中等厚度各向异性层合圆柱壳结构在轴压、外压和扭矩作用下的后屈曲行为的规律,为复合材料结构的设计提供科学依据;根据四步法1×1圆型编织工艺过程中编织纱线的运动轨迹特征和纱线的结构特点,将预成型件分为三个不同的区域,分别定义不同的控制体积单元,识别预成型件的局部单胞模型,分析预成型件的纱线构造,并推导出了编织结构参数之间的关系。编织结构主要的参数包括试件的外形尺寸、主体纱径向层数和周向列数、三个区域各自所占的体积百分比、纱线填充因子(缺省取为常数)、纤维体积含量、编织角以及编织花节长度。在预成型件分析的基础上,导出三维编织复合材料的局部单胞模型,分析复合材料的纱线构造,研究复合材料的编织结构参数之间的关系。从而,建立三维编织预成型件单胞弹性性能关系。采用三维应力-应变分析,在单胞的长度方向积分和平均,在给定的应变边界条件下,采用刚度体积平均的方法计算了单胞的有效弹性性能,预测三维编织结构复合材料的有效弹性模量。在此基础上提出一种三维四向编织复合材料圆柱壳的宏-细观力学模型。在壳体屈曲的边界层理论框架下,给出了三维编织复合材料圆柱壳在热环境下和在轴压、外压、扭矩及轴压和外压复合加载作用下的大挠度渐近解。分析中同时考虑前屈曲非线性变形,后屈曲大挠度和初始几何缺陷的影响,横向剪切变形的影响,以及材料物性参数对温度变化的依赖性。基于本文理论分析,用Fortran语言编制了相应的数值分析程序包,在上述研究领域内给出了大量的计算分析结果。本文得到国家自然科学基金:“混合智能结构非线性行为和动力特性建模与分析”(50375091)的部分支持。本文研究成果有助于推动纤维增强和三维编织复合材料结构的非线性稳定性的研究,对此两类复合材料结构在船舶和海洋工程中的应用具有积极意义。更多还原

【Abstract】 Currently there is a wide range of naval structures being developed using fibre-reinforced polymer composites, due to considerable strength-to-weight ratio. There has been considerable attention in the structural instability of relatively thick shells. Many current potential applications involve the moderately thick shell type configuration. For example, large patrol boats, hovercraft, minecountermeasure vessels and corvettes that are built completely of composite material, to mention a few. Other new or potential uses for composites are in the superstructures, advanced mast systems, bulkheads, decks, propellers, propulsion shafts and rudders for large surface combatants such as frigates and destroyers. In submarines, the future applications of composites may include control surfaces and mast systems. Navies are also exploring the feasibility of using composites for internal equipment and fittings, such as machinery, heat exchangers, equipment foundations, values, pumps, pipes and ducts. A new class of composite material known as braided composites have been received considerable attention. Textile composites are manufactured by fabrication methods derived from the textile industry. Unlike laminated composites, in which cracking and debonding may occur at high temperature due to the material property mismatch at the interface of two discrete materials, the textile composites are able to eliminate the delamination due to the inter-lacing of the tows in the through-thickness direction. Braided composites are now developed for general use as structural components in naval ship and submarine, offshore structures due to their light weight and easy handling secure their place in the industry.As a primary load carrying structure, the buckling and postbuckling behavior of laminated or braided cylindrical shell subjected to mechanical load is a vital safety consideration, and improvement of its prediction accuracy behavior is thus essential for reliable design.This paper consists of two parts: A boundary layer theory of shell buckling is extended to the case of general shear deformable anisotropic laminated cylindrical shell of finite length subjected to axial compression, external pressure, torsion, respectively. The material properties of each layer of the shell are assumed to be linearly elastic, anisotropic and fiber-reinforced. The governing equations are based on Reddy’s higher order shear deformation shell theory with von Kármán-Donnell-type of kinematic nonlinearity and including the extension/twist, extension/flexural and flexural/twist couplings. The nonlinear prebuckling deformations and initial geometric imperfections of the shell are both taken into account. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling response of perfect and imperfect, moderately thick, anisotropic laminated cylindrical shells with different values of shell parameters and stacking sequence.Then, established a micro-macro-mechanical model, a 3D braided composite may be as a cell system and the geometry of each cell is deeply dependent on its position in the cross-section of the cylindrical shell. The material properties of epoxy are expressed as a linear function of temperature. A postbuckling analysis is presented for a 3D braided composite cylindrical shell of finite length subjected to axial compression, external pressure, torsion, combined loading of external pressure and axial compression in thermal environments, respectively. The governing equations are based on Reddy’s higher order shear deformation shell theory with a von Kármán-Donnell-type of kinematic nonlinearity and including thermal effects. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling behavior of perfect and imperfect, braided composite cylindrical shells with different values of geometric parameter and of fiber volume fraction in different cases of thermal environmental conditions. The results show that the shell has lower buckling loads and postbuckling paths when the temperature-dependent properties are taken into account. The results reveal that the temperature changes, the fiber volume fraction, and the shell geometric parameter have a significant effect on the buckling load and postbuckling behavior of braided composite cylindrical shells.Finally, based on the present perturbation technique combined with perturbation method, the computer program packages are made by using FORTRAN computer language, this paper provides comprehensive first-ever-known results which are helpful in better understanding the postbuckling behavior of the 3D braided and fiber-reinforced shells.更多还原