复合加载条件下环肋柱壳的抗冲击屈曲能力分析

由Ｈａｍｉｔｏｎ变分原理导出非轴对称运动方程,本构关系采用增量理论,借助增量数值解法研究了复合载荷（轴向流－固冲击载荷＋径向均匀外压）条件下环肋圆柱壳的弹塑性动力屈曲。分别采用类似Ｂ－Ｒ准则和Ｓｏｕｔｈｗｅｌｌ方法来确定临界屈曲载荷,讨论了环肋骨和径向均匀压对圆柱壳结构抗冲击屈曲能力的影响。     

环向加筋圆柱壳轴向弹塑性动力屈曲

基于“离散加筋”模型,考虑了大挠度和材料硬化应变率敏感特性的影响,借助增量数值解法研究了环向加筋圆柱壳在轴向流－固冲击载荷作用下的弹塑性动力屈曲。分别采用类似B－R准则和Southwell方法来确定结构动力屈曲临界载荷。讨论了加强筋、材料硬化应变率敏感特性等因素对结构动力屈曲性态和临界载荷的影响。     

冲击块与金属圆柱壳相互作用的缓冲吸能分析

应用Johnson Cook本构方程, 结合Singace叠缩模型,考虑冲击作用引起材料的应变强化效应、应变率强化效应和温度效应,研究了冲击物体和金属圆柱壳相互作用的能量转化过程。运用角度增量叠缩法计算了圆柱壳的塑性变形能,根据冲击块和圆柱壳所组成系统能量守恒得到了冲击块速度位移、冲击块和圆柱壳之间瞬时载荷的解析表达式,以及圆柱壳塑性变形引起的温度分布函数。通过对不同材质的金属圆柱壳在冲击作用下塑性变形过程的计算分析,并和有限元计算结果比较,证明了本文计算方法的正确性。     

一般边界条件下受轴向冲击圆柱壳的动力特性计算分析

在受轴向冲击圆柱壳的非冲击端引入轴向、周向、径向和径向旋转4个方向边界弹簧模拟一般边界条件。根据Love薄壳理论得到圆柱壳变形过程中的应力应变,并采用一种改进的Fourier级数方法表示圆柱壳沿坐标轴方向的位移。将应力应变以及位移代入圆柱壳的能量表达式,采用基于Hamilton方程的一阶变分法对能量表达式进行推导和变换,得到一般边界条件下受轴向冲击圆柱壳的自然频率以及动力屈曲临界载荷的判别式。计算分析了一般边界条件对受轴向冲击圆柱壳的自然频率和屈曲临界载荷的影响,以及不同边界条件圆柱壳屈曲模态的类型特点。结果表明：一般边界条件下自然频率随着冲击载荷增大而降低;随着轴向波数的增加圆柱壳自然频率及屈曲临界载荷增大,随着周向波数的增加屈曲临界载荷也增大;轴向、周向、径向和径向旋转各个方向边界刚度对圆柱壳自然频率和屈曲临界载荷的影响都是刚度系数越小,自然频率越低而临界载荷越大;圆柱壳受轴向冲击,边界条件的改变会影响屈曲模态。     

三边简支一边固支矩形薄板动力屈曲解析解

根据板的动力平衡方程和压缩波前附加约束方程,基于双特征参数法和应力波理论,求解了三边简支一边固支矩形薄板在面内轴向冲击载荷作用下动力屈曲位移的解析解。揭示了矩形薄板动力屈曲过程中板的厚宽比、屈曲模态、冲击载荷大小和临界屈曲长度之间的关系。计算结果表明,由于横向惯性效应的存在,动力屈曲的临界载荷要比静力屈曲的大得多。     

冲击载荷作用下金属圆柱壳能量吸收研究

对Singace叠缩模型进行了修正,选用Johnson-Cook本构方程,研究冲击载荷的应变强化效应、应变率强化效应和温度效应下圆柱壳的吸能情况,利用分步叠缩的方法计算得到金属圆柱壳在冲击载荷作用下所吸收的能量值、温度的增加值和瞬时载荷-位移曲线,分析了圆柱壳的半径和厚度以及叠缩速度和能量吸收之间的关系     

大型风机柔性叶片摆振运动冲击对层间断裂韧性的影响

冲击对材料表面的层间断裂产生重要影响,但对层间断裂韧性影响的趋势尚不明确。尤其是风机叶片在摆振运动时,叶片所受冲击对叶片表面层间断裂的影响及趋势未见公开研究。本文首先对风机叶片摆振运动冲击载荷的动力学响应进行研究,确定振型-位移-速度的对应关系,然后对叶片摆振运动过程中的应力-应变-速度进行有限元数值分析,再依据连续介质力学原理建立摆振冲击载荷控制方程,明确摆振运动冲击导致裂缝的应变能释放率（G）和应力强度因子（K）的关系。最后通过对摆振和冲击实验中断裂参数（振型、位移、速度、载荷、起裂方式以及裂纹长度）的测量,验证了本文中摆振运动冲击对Ⅱ型裂缝层间断裂韧性的影响的研究结果,探讨了摆振运动冲击载荷对叶片表面层间断裂韧性影响的趋势。     

高分子材料应变松驰速率的表示方法

探讨采用应变松驰速率的概念描述硫化天然橡胶蠕变行为。结果表明,用ｕＳＡＲ＝４／∑ｉ＝１ε２／τ１ｅｘｐ（－ｔ／τｉ）速度方程,能较好地反映材料的应变松也变化规律以及载荷对材料应变松驰的影响,并认用ｖＳＡＲ描述硫化天然橡胶应变行为较为科学。     

排式矩形薄壁钢管横向冲击全屈曲模态解

研究钢管在横向冲击载荷下的屈曲大变形行为对抗爆及抗冲击吸能装置设计具有重要意义。根据实验结果,对钢管屈曲过程进行了简要分析,分阶段设定了钢管动力屈曲变形模态,并据此建立相应的位移、速度场,基于虚速度原理推导出了模态解控制方程,将问题转化为单一变量方程,便于下一步求解。结果表明,模态解方法是分析结构动态响应的有效近似方法,应变率效应是不可忽略的因素。     

α－钛／低碳钢爆炸复合界面结合层内的绝热剪切现象

本文利用光学显微镜和扫描电镜研究了α－钛／低碳钢爆炸复合界面结合层内α－钛侧产生的绝热剪切带（ＡＳＢ）的显微组织，表明ＡＳＢ内具有等轴晶组织特征，并且其内未发现微裂纹；显微硬度测量表明ＡＳＢ内的显微硬度比附近基体略高。并对ＡＳＢ这一现象从材料－力学－热学三方面进行了综合分析，认为，冲击载荷下绝热剪切是与速率相关的过程，应变率和应变都影响绝热剪切，材料本身的物理性能（定容比热Ｃ＿ｖ，密度ρ等），力学性能（如流变应力对应变率的敏感程度）和热性能（如热传导系数ｋ值）都影响ＡＳＢ的产生。     

Axisymmetric response of nonlinearly elastic cylindrical shells to dynamic axial loads

The axisymmetric response of nonlinearly elastic cylindrical shells subjected to dynamic axial loads is analysed by using an incremental formulation. The material elastic nonlinearity is modeled by the generalized Ramberg—Osgood representation. The time-dependent displacements of the shell are assumed to be governed by nonlinear equations of motion based on the von Karman—Donnell kinematic relations; moreover, both in-surface and out-of-surface inertia terms are included. The finite difference method with respect to the spatial coordinate and the Runge—Kutta method with respect to time are employed to derive a solution. Numerical results demonstrate the effect of the material nonlinearity on the deflections, stiffness matrices and dynamic buckling behavior of cylindrical shells.     

Thermal buckling of shallow/nonshallow piezoelectric-composite cylindrical shells

A thermal buckling analysis is presented for laminated cylindrical shells with surface mounted piezoelectric actuators under combined action of thermal and electrical loads. Derivations of the equations are based on the classical laminated shell theory, using the Sanders nonlinear kinematic relations. The analysis uses the Galerkin method to obtain closed form solutions for the buckling loads of shallow and nonshallow piezolaminated cylindrical shells. Temperature dependency of material properties is taken into account. Illustrative examples are presented to verify the accuracy of the proposed formulation. The effects of the various design parameters on thermal buckling loads are investigated.     

Nonlinear thermomechanical dynamic buckling analysis of imperfect viscoelastic composite/sandwich shells by a double-superposition global–local theory and various constitutive models

Almost no dynamic buckling analysis has been performed so far for the sandwich/multilayer viscoelastic shells. Even the vibration analyses of the mentioned shells have been restricted to the harmonic loads ignoring the transverse stresses and their continuity at the mutual interfaces of the layers, and the transverse flexibility of the shell. In the present paper, a high-order double-superposition global–local theory inherently suitable for nonlinear analyses is proposed and employed for nonlinear dynamic buckling and postbuckling analyses of imperfect viscoelastic composite/sandwich cylindrical shells subjected to thermomechanical loads. Depending on the nature of the applied loads, both complex modulus and hierarchical constitutive models are used for the viscoelastic materials. Results reveal that as the time duration of the suddenly applied loads decreases beyond the first natural period of the shell, the dynamic buckling load becomes much higher than the static buckling load, especially for the rectangular load–time histories. Furthermore, the relaxation behavior of the viscoelastic material may decrease the dynamic buckling load.     

Mechanical buckling of functionally graded material cylindrical shells surrounded by Pasternak elastic foundation

In this study, the mechanical buckling of functionally graded material cylindrical shell that is embedded in an outer elastic medium and subjected to combined axial and radial compressive loads is investigated. The material properties are assumed to vary smoothly through the shell thickness according to a power law distribution of the volume fraction of constituent materials. Theoretical formulations are presented based on a higher-order shear deformation shell theory (HSDT) considering the transverse shear strains. Using the nonlinear strain–displacement relations of FGMs cylindrical shells, the governing equations are derived. The elastic foundation is modelled by two parameters Pasternak model, which is obtained by adding a shear layer to the Winkler model. The boundary condition is considered to be simply-supported. The novelty of the present work is to achieve the closed-form solutions for the critical mechanical buckling loads of the FGM cylindrical shells surrounded by elastic medium. The effects of shell geometry, the volume fraction exponent, and the foundation parameters on the critical buckling load are investigated. The numerical results reveal that the elastic foundation has significant effect on the critical buckling load.     

外压作用下椭圆截面柱壳的弹性屈曲

基于能量法推导了外压作用下椭圆截面柱壳弹性屈曲临界荷载的理论解,推导中考虑了椭圆截面连续变化的曲率,引入带有衰减系数的位移函数以反映外压作用下椭圆柱壳的变形特点,并利用里兹法求解外压椭圆柱壳的能量方程。由椭圆柱壳理论解退化求得的圆柱壳外压屈曲荷载与已有文献的经典解吻合良好,与有限元分析结果的比较进一步验证了该文理论解的准确性。基于理论解的参数分析表明:在外压作用下,椭圆柱壳具备比圆柱壳更优越的力学性能;椭圆柱壳的外压屈曲荷载随椭圆截面比的增大而增大,随壳体名义径厚比的减小而增大;椭圆柱壳的外压屈曲荷载随壳体长度的增大而降低,但当名义长径比大于1左右后,屈曲荷载基本保持不变。     

确定轴向冲击下薄壁圆柱壳第二临界速度的新方法

研究薄壁圆柱壳的动态屈曲模式，有助于构造具有高吸能率的抗冲击结构。根据轴向冲击下的薄壁圆柱壳存在使其屈曲模式由轴对称转换为非轴对称的第二临界速度，且当冲击速度大于第二临界速度时薄壁圆柱壳的屈曲模式先呈现轴对称形式，然后随着冲击响应时间逐渐由轴对称形式转化为非轴对称形式这一理论，基于有限元仿真，比较撞击系统动能的时间历程和屈曲变形的时间历程，提出了用以确定第二临界速度的能量迭代法。应用此方法设计薄壁圆柱壳的动力屈曲结构可有效地减少试验次数，降低实验成本。该方法的可行性和正确性利用落锤实验得到了验证。     

A high-order theory for the analysis of circular cylindrical composite sandwich shells with transversely compliant core subjected to external loads

A new model based on the high order sandwich panel theory is proposed to study the effect of external loads on the free vibration of circular cylindrical composite sandwich shells with transversely compliant core, including also the calculation of the buckling loads. In the present model, in contrast to most of the available sandwich plate and shell theories, no prior assumptions are made with respect to the displacement field in the core. Herein the displacement and the stress fields of the core material are determined through a 3D elasticity solution. The performance of the present theory is compared with that of other sandwich theories by the presentation of comparative results obtained for several examples encompassing different material properties and geometric parameters. It is shown that the present model produce results of very high accuracy, and it is suggested that the present model, which is based on a 3D elasticity solution for the core material, can be used as a benchmark in future studies of the free vibration and buckling of circular cylindrical composite sandwich shells with a transversely compliant core.     

模态缺陷条件下复合材料柱形壳屈曲特性

为了开展多模态缺陷条件下复合材料柱形壳的屈曲特性研究,进行了理想柱形壳在轴压工况下的线性屈曲分析,得出前50阶屈曲失稳模式,即模态缺陷;基于弧长法研究不同模态缺陷条件下复合材料柱形壳的非线性屈曲特性;将有限元分析结果、NASA SP-8007规范计算结果与Bisagni试验结果作对比分析。结果表明:对于轴压柱形壳屈曲问题,第1阶模态缺陷不是最差缺陷,在第1阶模态缺陷条件下求出的非线性屈曲载荷比试验值高出较多;高阶模态缺陷条件下的复合材料柱形壳非线性屈曲计算结果与试验结果最为吻合,两者相差较少;屈曲载荷下降受缺陷形状、幅值双重影响,复合材料柱形壳屈曲计算需考虑多模态问题;NASA求出的屈曲载荷非常保守,低于试验值较多,用NASA方法进行复合材料柱形壳的设计,往往会导致结构笨重、材料浪费、性能降低。     

Numerical analysis of dynamic buckling of rectangular plates subjected to intermediate-velocity impact

This paper numerically investigates the dynamic buckling of thin imperfect rectangular plates subjected to intermediate-velocity impact loads. From numerical results obtained, a dynamic buckling and a dynamic yielding critical condition are defined, and the corresponding critical dynamic loads are estimated. Numerical model employed in the present study is validated by experimental data reported earlier. Results from parametric study indicate that initial imperfection and load duration have significant influence on the dynamic buckling of the plates. The smaller the initial imperfection and the load duration, the higher the dynamic buckling critical loads of the plates. Moreover, different hardening ratios of plate material also affect the elastic–plastic dynamic buckling properties of the plates. If the plate buckles plastically, the dynamic buckling load increases as the hardening ratio of plate material increases. Unlike thin plates under high-velocity impact that buckling always occur after load application, plates under intermediate-velocity impact analyzed in the present study all buckle during the loading phase.