脱层复合材料圆柱壳屈曲的实验研究

脱层的存在将会大大降低层合结构的屈曲载荷.本文首先针对在轴压载荷作用下含脱层的复合材料层合圆柱壳,设计了测试其稳定性的实验方案.然后利用位移传感器、应变传感器、声发射仪器和红外热像仪等实验仪器,对含任意位置脱层与不含脱层的圆柱壳的屈曲载荷进行了实验测试,并对实验进行了精度分析.最后给出了实验结果并进行了讨论.     

激光扫描法建模在开孔圆柱壳轴压屈曲中的应用

采用激光位移传感器对开孔圆柱壳的三维形貌进行测量,基于实测数据建立有限元模型,利用ABAQUS对不同开孔率的圆柱壳进行非线性有限元分析,模拟结果显示:载荷位移曲线先线性增大,后出现突变,轴向压力迅速减小,轴压屈曲临界载荷随着开孔率增大而减小。对开孔率为5%,10%,15%的圆柱壳进行轴压屈曲试验,试验采用液压装置进行轴压,轴压数据通过称重传感器获得。对轴压屈曲临界载荷模拟值与试验值进行比较,最小的相对误差只有10.8%。说明运用激光扫描法建模进行非线性有限元分析,可以较好地预测开孔圆柱壳轴压屈曲临界载荷。     

层合多孔圆柱壳轴向压缩实验与仿真研究

使用实验测试和有限元仿真计算的方法，研究了层合多孔圆柱壳在轴向压缩荷载下的承载力性能和变形破坏模式。考虑正六边形和内凹六边形两种多孔构型，讨论了高度、直径、厚度参数对层合多孔圆柱壳轴向承载力的影响，得到了内凹多孔圆柱壳的轴压性能优于正六边形圆柱壳的结论。分析了层合多孔圆柱壳轴向压缩下的屈曲变形模式。同时，使用测试得到的材料参数仿真模拟实验结果，对照分析了仿真与实验变形特征与压缩性能。     

弹性圆柱壳的稳定性优化设计

研究任意轴对称边界条件下和受均布法向载荷作用圆柱壳的稳定性优化设计问题，即极大化屈曲临界载荷。利用能量原理分析轴对称变厚度圆柱壳的分支点屈曲，将求解屈曲临界载荷变成求解广义特征值方程，使圆柱壳稳定性优化设计成为极大化最小特征值问题。实际算例验证了本方法的有效性。研究结果可用于圆柱壳的加肋优化设计。     

轴向冲击载荷下圆柱壳动力屈曲的计算机仿真

圆柱壳是工程中最常用的结构元件之一,对圆柱壳在各种基本载荷以及在不同类型载荷的联合作用下的屈曲问题研究一直是应用力学界和结构工程界十分关注的课题,与静力屈曲相比,圆柱壳的动力屈曲问题的研究还不尽完善.文章通过有限元软件ANSYS研究圆柱壳轴向冲击下的动力屈曲问题.     

构型参数对格栅圆柱壳侧压稳定性影响研究

基于有限元参数化建模方法,开展了受侧压格栅圆柱壳的稳定性分析。在总体积相同情况下,以正交格栅、正交各向异性格栅、等格栅圆柱壳为研究对象,分析了圆柱壳包含不同体胞数、不同体胞构型以及给定体胞数时蒙皮厚度、筋骨尺寸变化对结构临界屈曲载荷、失稳模式的影响。计算结果表明:等体积下,格栅圆柱壳存在最佳匹配的体胞构型和体胞数来最大化临界屈曲载荷;侧压圆柱壳最大临界屈曲载荷发生在局部失稳与整体失稳的过渡区。     

含脱层复合材料连接件的挤压强度试验研究

脱层是复合材料层板结构中的主要缺陷形式之一,它的存在会造成脱层的局部屈曲和扩展,从而降低结构的攻刚度。本工作对含脱层的复合材料螺栓连接件在静载,疲劳载荷和湿热环境载荷的作用下进行了试验研究。测定了含脱层的复合材料连接件的局部失稳载荷,挤压强度和疲劳寿命数值。探讨了脱层尺寸对局部失稳载荷,挤压强度和疲劳寿命的影响大小,给出了疲劳寿命和脱层直径的函数曲线探讨了含脱层的复合材料连接件在湿热环境下的强度和     

纵向波纹柱形耐压壳屈曲数值分析与试验研究

采用周向或轴向波纹,增强圆柱形耐压壳(简称圆柱壳)的承载能力已备受关注。采用数值与试验结合的方法,研究等容积圆柱壳和纵向波纹柱形耐压壳(简称波纹柱壳)的屈曲特性。首先,建立波纹柱壳的几何模型和数值模型,分析均布外压作用下,波纹参数变化对波纹柱壳屈曲特性的影响规律;其次,依据承载能力进行波纹参数优化设计,并制造两组等壁厚和等容积的圆柱壳和波纹柱壳实物模型;再次,测量两种模型的实际几何数据,分别建立其数值模型,并进行屈曲特性分析;最后,对圆柱壳和波纹柱壳的实物模型进行静水压力试验,与数值结果作对比分析。结果表明:均布外压下,等容积纵向波纹柱壳的屈曲性能优于柱形壳,其平均屈曲载荷提高了56.8%,纵向波纹改善了圆柱壳的承载能力。     

正置正交加筋薄壁柱壳优化设计参数化有限元方法研究

利用有限元软件建立轴压正置正交加筋薄壁圆柱壳的参数化有限元分析模型,研究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。随着蒙皮厚度的增加,结构的屈曲模式由局部屈曲逐步变化到总体屈曲,屈曲载荷上升;随着加筋厚度或宽度的增加,由总体屈曲变化到局部屈曲,屈曲载荷上升。通过等体积时的参数变化对屈曲载荷和屈曲模式的影响研究,表明在对应某体积的设计中,只有一种设计使结构屈曲载荷达到最大,而当此最大的屈曲载荷等于设计载荷时,是最轻重量的设计。在此基础上发展一种基于APDL(Ansys parametric design language)语言的薄壁加筋圆柱壳结构优化设计方法,利用该方法给出设计算例的优化结果。     

含初始几何缺陷薄壁圆柱壳屈曲载荷的数值模拟方法研究

对3个薄壁圆柱壳试件进行了轴压屈曲试验,得到了屈曲临界载荷值和屈曲变形。基于试验结果,比较了弧长法、非线性稳定算法和显式动力算法3种有限元数值模拟方法的差异,其中非线性稳定算法的模拟结果与试验结果吻合最好,该方法可以比较准确地计算轴压屈曲临界载荷,误差在6.0%以内,且屈曲变形与试验吻合得较好。试验表明,初始几何缺陷的存在大幅降低了薄壁圆柱壳的屈曲临界载荷,试验值仅为理论值的42%左右。     

Buckling of composite beams with two non-overlapping delaminations: Lower and upper bounds

In this paper, lower and upper bounds of the buckling load of a composite beam with two non-overlapping delaminations are obtained by developing analytical models. The characteristic equation governing the delamination buckling is derived by using Euler-Bernoulli beam theory, performing proper linearization and by imposing the appropriate continuity and boundary conditions. The effects of the differential stretching and the bending-extension coupling are considered. The accuracy of the approach is verified by comparing results with previously published data and a separately carried out finite element analysis. The effects of the dimensions of the delaminations, their thicknesswise and spanwise locations on the lower and upper bounds of the buckling load are investigated in detail. The longer of the two non-overlapping delaminations dominates the buckling behavior. Composite beams with anti-symmetric non-overlapping delaminations withstand lower buckling loads than the composite beams with symmetric non-overlapping delaminations. The lower and upper bounds of the buckling load will be useful to gauge the working range of bridging and give guidelines for practical applications.     

Buckling analysis of a laminated composite plate with delaminations using the enhanced assumed strain solid shell element

The paper deals with the validation of a recently proposed hexahedral solid-shell finite element in the buckling analysis of a laminated composite plate with delaminations. The object is to study the buckling behavior of structures with delaminations using the enhanced assumed strain (EAS) solid shell element with 5, 7 and 9 parameters. The EAS three-dimensional finite element formulation presented in this paper is free from shear locking and leads to accurate results for distorted element shapes. The developed FE model is used to study the effects of some parameters in the buckling load, such as the stacking sequences, delamination size, aspect ratio, width-to-thickness ratio. The feasibility of the proposed method is confirmed by numerical examples. Results show that using hexahedral solid-shell finite element in the buckling analysis is more efficient than using the enhanced solid finite element.     

Nonlinear elastic buckling and postbuckling of axially compressed functionally graded cylindrical shells

Based on the nonlinear large deflection theory of cylindrical shells as well as the Donnell assumptions, this paper presents nonlinear buckling and postbuckling analyses for axially compressed functionally graded cylindrical shells by using the Ritz energy method and the nonlinear strain-displacement relations of large deformation. The material properties of the shells vary smoothly through the shell thickness according to a power law distribution of the volume fraction of constituent materials. Meanwhile, by taking into account the temperature-dependent material properties, various effects of external thermal environment are also investigated. Numerical results show various effects of the inhomogeneous parameter, dimensional parameters and external thermal environments on nonlinear buckling and postbuckling behaviors. There is a mode-jumping observed after buckling. The present theoretical results are verified by those in the literature.     

Theory and comparison of the effect of composite and shape memory alloy stiffeners on stability of composite shells and plates

The effects of composite and shape memory alloy stiffeners on stability of composite cylindrical shells and rectangular plates subjected to a compressive load are compared. The governing equations for reinforced cylindrical shells are developed based on the Love first approximation theory and smeared stiffeners technique. It is shown that composite stiffeners are more efficient in cylindrical shells, while shape memory alloy stiffeners may be preferable in plates or in long shallow shells. It is also proven that shape memory alloy stiffeners increase the upper and lower buckling loads, i.e. the linear buckling load and the minimum postbuckling load-carrying capacity of cylindrical shells modeled as single-degree-of-freedom systems by the same amount.     

Post-buckling and delamination propagation behavior of composite laminates with embedded delamination

Delamination occurred due to poor manufacturing process or in-service actions significantly affects the mechanical and failure behavior of laminated composite structures. In this study, the buckling and post-buckling delamination behavior of laminated composite with an embedded initial delamination under in-plane compression was studied experimentally and numerically. First, compression tests for laminated composite specimens with embeded initial delamination were performed and the buckling and delamination responses were obtained. Then the experimental test was numerically simulated using finite element methods with the progressive failure accounted for by using cohesive zone modeling. The load-displacement curve, strain behavior and delamination shapes of experimental specimens obtained from load cells, strain gages installed at different locations, and C scan images, respectively, were compared with the FEM results, and good agreements were attained. The effect of the buckling modes, laminate stacking sequence and shape of initial delamination on the buckling load and propagation behavior was studied by considering different ply stacking and shapes of initial delaminations. It was found that the buckling mode determined the growth direction of the delamination propagation, and the stacking sequence influenced the extent of the propagation area, while the orientation of the delamination affected the buckling loads.     

Deformation and failure mechanisms of lattice cylindrical shells under axial loading

The lattice cylindrical shells wound from the planar lattice plates, which have significant applications in aerospace engineering, exhibit different deformation modes with their planar counterparts because of the curvature of the cell wall. In this paper, deformation mechanisms are systematically investigated and failure analyses are conducted for the lattice cylindrical shells with various core topologies. Analytical models are proposed to predict the axial stiffness, critical elastic buckling load or effective yield strength of these shells. Finite element simulations are carried out to identify the validity of the models. The models can be employed for the optimal design. As an example, we construct the failure map for the Kagome lattice cylindrical shell made from an elastic ideally-plastic material. Various failure mechanisms, including yielding, global elastic buckling and local elastic buckling are taken into account. Moreover, optimizations are performed to minimize the weight for a given stiffness or load-carrying capacity for three types of lattice cylindrical shells. It is found that the Kagome and triangular lattice cylindrical shells have almost equivalent load-bearing capacity and both significantly outperform the hexagonal one under axial compression.     

Investigating elastic stability of cylindrical shell with an elastic core under axial compression by energy method

In this paper, the elastic axisymmetric buckling of a thin, isotropic and simply supported cylindrical shell with an elastic core under axial compression has been analyzed using energy method. The nonlinear strain-displacement relations in general cylindrical coordinates are simplified using Sanders kinematic relations (Sanders, 1963) for axial compression. Equilibrium equations are obtained by using minimum potential energy together with Euler equations applied for potential energy function in cylindrical shell. To acquire stability equation of cylindrical shell with an elastic core, minimum potential energy theory and Trefftz criteria are implemented. Stability and compatibility equations for an imperfect cylindrical shell with an elastic core are also obtained by the energy method, and the buckling analysis of shell is carried out using Galerkin method. Critical load curves versus the aspect ratio are obtained and analyzed for a cylindrical shell with an elastic core. It is concluded that the application of an elastic core increases elastic stability and significantly reduces the weight of cylindrical shells.     

三维编织复合材料高压储气瓶的屈曲分析与优化设计

通过对三维编织复合材料圆柱壳进行屈曲和应力分析，对三维编织复合材料高压储气瓶的临界载荷、强度和应力分布等进行了数值计算，结果表明，屈曲对三维编织复合材料高压储气瓶使用性能的影响非常显著。基于圆形四步法三维编织工艺及理论分析，提出了三维编织复合材料高压储气瓶的结构优化设计数学模型。算例表明，该优化设计方法效果很好。