材料应变率对圆柱壳轴向冲击屈曲的影响

研究了轴向冲击载荷作用下材料应变率对圆柱壳弹塑性冲击屈曲的影响,采用Ｋａｒｍａｎ－Ｄｏｎｎｅｌｌ运动方程,本构关系采用增量理论,联立Ｃｏｗｐｅｒ－Ｓｙｍｏｎｄｓ关系,求得相应的动屈服应力,借助增量数值计算方法注解运动方程,计算表明：材料的应变率敏感性显著地提高了结构的抗冲击屈曲能力;基于Ｂ－Ｒ准则的屈曲判断方法和采用Ｓｏｕｔｈｗｅｌｌ方法可以获得一致的临界屈曲载荷。     

轴压薄壁加筋圆柱壳结构优化设计研究

分别建立了轴向载荷作用下正置正交薄壁加筋圆柱壳结构优化设计的数学模型和有限元分析模型,应用Ansys软件进行优化计算,讨论了外载荷、材料屈服极限对优化设计的影响,以及结构参数对薄壁加筋圆柱壳结构的临界载荷和屈曲模式的影响。基于有限元分析的研究结论,发展了一种薄壁加筋圆柱壳结构优化设计方法,给出设计算例的优化结果,并将两...     

冲击载荷下圆环压缩变形特性研究

基于Johnson-Cook材料模型,应用数值模拟的方法,研究了圆环件在冲击载荷作用下的压缩变形规律。得到了冲击载荷下的摩擦系数-变形特性曲线,由此研究了不同载荷幅值(加载速度)、不同应变率敏感系数下的圆环内径变化规律以及对临界摩擦系数的影响。结果表明:摩擦系数-变形特性曲线和准静态结果基本趋势一致但有较大的差异,其中惯性效应起主要作用,应变率效应则起着次要作用。另外,此过程存在着临界摩擦系数,而应变率效应和惯性效应对圆环的临界摩擦系数影响不大,因此,临界摩擦系数可以作为试件的内在属性,应用于圆环的冲击锻压工程。     

轴向时变冲击载荷作用下直杆弹性动力屈曲研究

基于应力波理论,用半解析半数值方法对轴向时变冲击载荷作用下的直杆进行研究,给出了一种利用压应力波前附加约束条件求解轴向时变载荷作用下直杆弹性动力屈曲问题的方法。以三角脉冲载荷作用下的直杆为例,对其临界屈曲长度、初始屈曲模态和动力特征参数进行了求解,探讨了脉冲载荷峰值和载荷持续时间对临界屈曲长度和屈曲模态的影响。总结了三角脉冲载荷作用下直杆弹性动力屈曲的规律,并与阶跃载荷作用下的情况进行对比分析,结果与之前文献研究结果吻合良好。     

爆炸冲击载荷下耐压鞍形舱壁结构弹塑性动力屈曲

本文借助有限元软件ANSYS/LS-DYNA对耐压鞍形舱壁结构在爆炸冲击载荷作用下的弹塑性动力屈曲进行了研究。采用Budiansky-Roth屈曲准则判断鞍形舱壁的动力屈曲,研究了初始缺陷大小对鞍形舱壁结构动力屈曲的影响,并与等重量的传统三心球面舱壁结构进行了对比,然后讨论了主要设计参数对鞍形舱壁结构动力屈曲的影响。研究表明：鞍形舱壁结构比等重量的三心球面舱壁结构动力屈曲载荷有明显提高,且对初始缺陷不敏感,合理的匹配各设计参数可以使舱壁结构的动力屈曲性能达到最佳。     

含阻尼杆的中速冲击屈曲性能研究

本文对考虑阻尼的杆在轴向冲击作用下的动力屈曲性能进行了理论分析，通过采用Ｒａｙｌｅｉｇｈ阻尼理论，对动力屈曲控制方程解耦得一变系数微分方程，在分析方程解的基础上，探讨了阻尼对轴向冲击杆动力屈曲性能的影响，揭示了含阻尼结构的动力屈曲现象，定义了动力屈曲准则及确定阻尼杆临界载荷参数的方法．     

基于屈曲准则的瓦楞纸板强度仿真分析

分别建立了典型的A、C、B楞型单瓦楞纸板的有限元模型,计算了3种瓦楞纸板的临界屈曲载荷。以临界屈曲载荷为纸板抗压能力的判定准则,定量分析了3种瓦楞纸板的抗压能力,同时研究了材料与结构对瓦楞纸板抗压能力的影响及每种瓦楞纸板的材料抗压效率。分析结果表明,大瓦楞有更好的抗压能力,其抗压能力的提高主要是依靠其结构实现的,约束条件能够极大地改变瓦楞纸板的抗压效率。     

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。     

湿热环境对航空复合材料加筋板压缩屈曲和后屈曲性能的影响

使航空复合材料加筋板在湿热环境中(70°C、水浴)达到吸湿饱和状态,对普通加筋板(A型)和吸湿饱和加筋板(B型)进行压缩实验。两类加筋板的破坏形貌相似,主要是筋条的断裂、脱粘和壁板的分层、撕裂,但破坏位置显著不同,A型加筋板的破坏位置均在加筋板中部附近,而B型分别在靠近两端的部位破坏,表明B型加筋板的破坏位置具有不确定性。两类加筋板的屈曲形式均为筋条间壁板的屈曲和中间2根筋条的屈曲,但两类加筋板相同位置的失稳壁板的弯曲方向相反,说明湿热环境对失稳壁板的弯曲方向影响较大。B型加筋板在压缩载荷下仍存在后屈曲过程,湿热环境对加筋板的屈曲载荷影响较小,对破坏载荷影响较大,较A型加筋板相比两者分别下降了3.1%和22.2%。     

复合材料帽型加筋板轴压试验及承载能力预测

随着复合材料的广泛使用,复合材料帽型加筋板在飞机结构上的使用也越来越多。为研究复合材料帽型加筋板承受轴向压缩的能力,首先对不同蒙皮半径、蒙皮厚度及长桁间距的复合材料帽型加筋板进行了轴压试验,得到了局部屈曲载荷、破坏载荷与加筋板曲率系数、长桁间距的关系,然后,通过引入曲率修正系数,修正了现有加筋板屈曲载荷的工程估算公式;最后,利用分段处理法结合有效宽度概念改进了加筋板轴压极限承载的工程算法。结果表明:帽型复合材料加筋板局部屈曲载荷及最终破坏载荷与曲率系数正相关;改进的方法能对复合材料加筋板的极限承载进行准确预测。所得结果表明该方法为复合材料加筋板结构设计及载荷估算提供了一种新方法,具有一定的工程应用价值。      

Inertia effects in axisymmetrically deformed cylindrical shells under axial impact

The axisymmetric buckling of elastic–plastic cylindrical shells subjected to axial impact are studied using a finite element analysis. This study reveals that shells, subjected to axial impact, are both velocity and mass sensitive, so that larger energies can be absorbed by a shell for high-velocity impacts when decreasing the striking mass. It is shown that the inertia characteristics of the shell, together with the material properties, determine particular patterns of the axial stress wave propagation, thus, causing either dynamic plastic or dynamic progressive buckling to develop during the initial phase of the shell response. Domains of the load parameters, where the different buckling phenomena develop, are obtained for two particular shells. Strain rate effects are also considered when discussing the energy absorbing properties of the shells.     

Buckling of FGM cylindrical shells subjected to pure bending load

In this paper, buckling behaviors of composite cylindrical shells made from functionally graded materials (FGMs) subjected to pure bending load were investigated. The material properties were assumed to be graded along the thickness. The non-uniform bending force on the shell section was considered in the buckling government equation of FGM cylindrical shells based on the Donnell shallow shell theory. The prebuckling deformation of the FGM cylindrical shells was neglected and the buckling mode was assumed to occur non-uniformly in local district along the shell circumferential direction. The eigenvalue method was used to obtain the buckling critical condition. The theoretical results were in excellent agreement with those of ABAQUS code. Results show that the inhomogenity of the materials is significant for buckling of FGM cylindrical shells.     

Nonlinear dynamic buckling of functionally graded cylindrical shells subjected to time-dependent axial load

This paper is presented to solve the nonlinear dynamic buckling problem of a new type of composite cylindrical shells, made of ceram/metal functionally graded materials. The material properties vary smoothly through the shell thickness according to a power law distribution of the volume fraction of the constituent materials. The dynamic axial load is set in a linear increase form with regard to time. By taking the temperature-dependent material properties into account, the effect of environmental temperature rise is included. The nonlinear dynamic equilibrium equation of the shell was obtained by applying an energy method, and was then solved using the four-order Runge–Kutta method. The critical condition was eventually determined using B-R dynamic buckling criterion. Numerical results show the dynamic buckling load is higher than its static counterpart. Meanwhile, various effects of the inhomogeneous parameter, loading speed, dimension parameter, environmental temperature rise and initial geometrical imperfection on nonlinear dynamic buckling are discussed.     

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.     

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.     

Performance of a fiber reinforced polymer web core skew bridge superstructure. Part I: field testing and finite element simulations

An analytical method is presented to investigate hydrothermal effects on locally buckling for an elliptical delamination near the surface of cylindrical laminated shells. The critical strain of non-linear buckling for a locally elliptic delamination of cylindrical laminated shells is obtained by considering transverse displacements of the elliptically sub-laminated shells. The stacking sequence of sub-laminated shells may be multilayer and asymmetric. The geometrical axis of sub-laminated shells may be arbitrary. The Young's modulus and the thermal and humidity expansion coefficients of the material are considered as functions of temperature change in base-laminated shells. The critical strains of locally buckling for cylindrical laminated shells subjected to hydrothermal effects are extracted for different stacking sequences, and different radii of base-laminated shells, by applying Rayleigh–Ritz method based on second variation of potential energy. From results carried out, it is found that the critical strain from the non-linear buckling for a locally elliptic delamination near the surface of a cylindrical laminated shell presents a lower value than that from linear considerations.     

Postbuckling of pressure-loaded FGM hybrid cylindrical shells in thermal environments

A postbuckling analysis is presented for a functionally graded cylindrical shell with piezoelectric actuators subjected to lateral or hydrostatic pressure combined with electric loads in thermal environments. Heat conduction and temperature-dependent material properties are both taken into account. The temperature field considered is assumed to be a uniform distribution over the shell surface and varied in the thickness direction and the electric field considered only has non-zero-valued component E_Z. The material properties of functionally graded materials (FGMs) are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and the material properties of both FGM and piezoelectric layers are assumed to be temperature-dependent. The governing equations are based on a higher order shear deformation theory with a von Kármán–Donnell-type of kinematic nonlinearity. A boundary layer theory of shell buckling is extended to the case of FGM hybrid laminated cylindrical shells of finite length. A singular perturbation technique is employed to determine the buckling pressure and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling behavior of pressure-loaded, perfect and imperfect, FGM cylindrical shells with fully covered piezoelectric actuators under different sets of thermal and electric loading conditions. The results reveal that temperature dependency, temperature change and volume fraction distribution have a significant effect on the buckling pressure and postbuckling behavior of FGM hybrid cylindrical shells. In contrast, the control voltage only has a very small effect on the buckling pressure and postbuckling behavior of FGM hybrid cylindrical shells.     

Delamination buckling and postbuckling in composite cylindrical shells under combined axial compression and external pressure

A series of finite element analyses on the delaminated composite cylindrical shells subject to combined axial compression and pressure are carried out varying the delamination thickness and length, material properties and stacking sequence. Based on the FE results, the characteristics of the buckling and postbuckling behaviour of delaminated composite cylindrical shells are investigated. The combined double-layer and single-layer of shell elements are employed which in comparison with the three-dimensional finite elements requires less computing time and space for the same level of accuracy. The effect of contact in the buckling mode has been considered, by employing contact elements between the delaminated layers. The interactive buckling curves and postbuckling response of delaminated cylindrical shells have been obtained. In the analysis of post-buckled delaminations, a study using the virtual crack closure technique has been performed to find the distribution of the local strain energy release rate along the delamination front. The results are compared with the previous results obtained by the author on the buckling and postbuckling of delaminated composite cylindrical shells under the axial compression and external pressure, applied individually.     

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。