Buckling of moderately thick laminated cylindrical shells: a review

The present paper is a review article on the problem of buckling of moderately thick, laminated, composite shells subjected to destabilizing loads. The loads consist of uniform axial compression, uniform lateral pressure and torsion applied individually or in combination. In all the works reported in the literature, the analysis is based on higher-order shear deformation (HOSD) shell theory and/or first-order shear deformation (FOSD) shell theory with or without a shear correction factor. Results obtained by these two shell theories and by employing classical thin shell theory are compared to determine the range of applicability of each in predicting critical conditions. The effect of stacking sequence, radius-to-thickness ratio and length-to-radius ratio is assessed. Typical numerical results are presented in tabular form. Moreover, some limited results, which are based on limit point analysis are also presented (imperfection sensitivity studies).     

轴对称胀形双曲金属薄壳非线性静力分析

对承受内压、非等厚轴对称双曲薄壳,基于大塑性变形几何关系,通过严格的数学推导,建立了用微分代数方程组描述的数学模型。避免了Gleyzal等建立的变形几何关系采用Taylor展开,导致求解大应变问题精度较低的不足。采用可变步长和变阶的Klopfenstein-Shampine数值微分方法进行计算,可方便地获得该类结构应力、应变和位移等参量的变化规律。通过对比该数学模型和基于Gleyzal几何关系数学模型的数值计算结果与试验结果,验证了模型能较好地描述胀形双曲金属薄壳的大应变特性。     

椭球壳体无模液压成形实验探索

对椭球壳体的整体无模胀形成形工艺进行了实验研究。实验壳体采用单曲率椭球内接多面壳体。对实验壳体的尺寸变化、变形过程中的表面应变分布、变形前后的壁厚变化规律进行了测试分析,探讨了壳体的趋球变形过程,壳体的长短轴变化趋势及塑性变形规律。实验证明,在封闭椭球壳体内塑性趋球规律仍然起作用,椭球无模液压整体成形工艺值得进一步探讨研究。     

分析部分环状覆盖PCLD圆锥壳自由振动与阻尼特性的半解析法

基于Donnell薄壳和线粘弹性理论,对于粘弹性层仅考虑剪切变形,并采用复常量模型模拟粘性层的能耗特性,导出了PCLD圆锥层合壳的整合一阶常微分矩阵方程,由于周向曲率是纵向坐标的函数,系数矩阵比圆柱层合壳复杂。然后借助精细积分和传递矩阵法,提出了一种分析部分覆盖PCLD圆锥层合壳自由振动和阻尼特性的半解析方法。通过数值算例证明了本文方法的有效性,文中还讨论了覆盖率等参数对PCLD圆锥层合壳固有频率和损耗因子的影响,影响程度和PCLD圆柱层合壳也不同。     

A four‐node corotational quadrilateral elastoplastic shell element using vectorial rotational variables

A four‐node corotational quadrilateral elastoplastic shell element is presented. The local coordinate system of the element is defined by the two bisectors of the diagonal vectors generated from the four corner nodes and their cross product. This local coordinate system rotates rigidly with the element but does not deform with the element. As a result, the element rigid‐body rotations are excluded in calculating the local nodal variables from the global nodal variables. The two smallest components of each nodal orientation vector are defined as rotational variables, leading to the desired additive property for all nodal variables in a nonlinear incremental solution procedure. Different from other existing corotational finite‐element formulations, the resulting element tangent stiffness matrix is symmetric owing to the commutativity of the local nodal variables in calculating the second derivative of strains with respect to these variables. For elastoplastic analyses, the Maxwell–Huber–Hencky–von Mises yield criterion is employed, together with the backward‐Euler return‐mapping method, for the evaluation of the elastoplastic stress state; the consistent tangent modulus matrix is derived. To eliminate locking problems, we use the assumed strain method. Several elastic patch tests and elastoplastic plate/shell problems undergoing large deformation are solved to demonstrate the computational efficiency and accuracy of the proposed formulation. Copyright © 2013 John Wiley & Sons, Ltd.     

壳间连接形式对双层壳声辐射性能的影响

研究流场中受径向点激励的有限长双层圆柱壳壳间用实肋板连接或用托板连接对其振动和声辐射性能的影响。壳体的振动用Flügge壳体方程描述,将加强构件等价为对内外壳体的支持力,实肋板作用可以等价为周向、轴向和径向三个方向的力和轴向弯矩作用到壳体上。托板近似简化为拉压杆件进行计算,并推导了托板的动反力公式,然后将其引入壳体振动方程,最后求解双壳体声-流体-结构耦合方程,计算结果用辐射声功率、表面振动均方速度级和辐射效率的形式表示。在数值分析部分,讨论了壳间连接型式变化对双层圆柱壳的声辐射性能的影响,分析了托板和实肋板的差别。得出结论:壳间连接越紧密,对应的双层加筋圆柱壳的辐射声功率越高。     

Aeroelastic stability of heated functionally graded cylindrical shells containing fluid

The article is concerned with the analysis of panel flutter of heated circular clamped cylindrical shells made of functionally graded (FG) material, which are subject to a simultaneous action of the external supersonic gas flow and the internal flow of ideal compressible fluid. The effective properties of the material change throughout the thickness of the shell according to a power law and depend on temperature. The aerodynamic pressure is calculated based on the quasi-static aerodynamic theory. The behavior of the fluid is described in the framework of the potential theory. A mathematical formulation of the dynamic problem for elastic structure is developed based on the classical theory of shells and the principle of virtual displacements. Based on the results of numerical simulation the influence of different consistencies of the examined FG materials, thermal load, and internal flow velocity on the boundary of aeroelastic stability is analyzed.     

氮化铝一维纳米结构制备方法和物性研究的最新进展

全面总结了近年来氮化铝一维纳米结构的各种制备方法及物理性能等研究的最新进展,并提出了有待进一步深入研究的一些发展方向。