含单分层损伤复合材料层合梁的动力屈曲研究

采用有限差分（FDM）方法求解了含初始缺陷和单个分层损伤复合材料层合梁的轴向刚性质量块撞击的脉冲动力屈曲问题。基于Hamilton原理导出了考虑所有惯性影响以及一阶横向剪切变形（FSDT）影响时单个分层损伤复合材料梁的非线性动力屈曲控制方程；采用B—R准则判断梁动力屈曲时刻，同时确定刚性质量块的临界冲击速度。重点研究脱层、冲击速度、初始几何缺陷等因素对复合材料层合梁脉冲动力屈曲的影响。     

含脱层单向铺设层合梁非线性后屈曲分析

采用四分区模型,将含脱层单向铺设复合材料层合板梁分为4个子梁,根据复合材料层合理论,考虑后屈曲路径上位于脱层界面上、下子梁之间的局部受力与变形机制,建立了子梁之间接触力与变形之间的非线性定量关系。在此基础上,结合可伸长梁的几何非线性理论,推导出了计及接触效应的各子梁的非线性后屈曲控制方程。设定简支板梁的边界条件以及脱层前沿处各子梁之间力和位移的连续性条件,通过对控制方程和定解条件归一化,采用小参数摄动法求解,并根据梁的平衡微分方程的特点,解析其通解与特解的构造,获得了含脱层单向铺设层合梁受轴向压力作用的临界屈曲荷载及后屈曲平衡路径的理论解。通过对含脱层单向铺设的复合材料层合梁进行数值分析,综合讨论了脱层长度和深度等对层合板梁的临界屈曲载荷及接触性能的影响,并将所得的理论解与ABAQUS有限元分析得到的结果进行对比,结果表明二者高度吻合。研究发现梁的屈曲模态包含宏观的整体失效模态和界面的微观屈曲模态。梁的屈曲荷载和接触性能都是其固有属性,前者受梁的几何参数和材料参数的影响较显著,而后者则主要受脱层的位置和大小影响。     

冲击载荷下复合材料层合杆的动力屈曲

研究复合材料层合杆被一质量块以某一速度沿轴向进行碰撞而导致的动力屈曲现象,采用不同的横向剪切理论,并用差分方法对杆的动力屈曲方程进行求解。文中考察了冲击块质量、初挠度、应力波、横向剪切等因素对临界冲击速度以及屈曲模态的影响。     

含环向贯穿脱层的轴压圆柱层壳屈曲分析:I——基本方程与定解条件

复合材料层合圆柱壳是一种常用的承载结构,在其制造、运输和使用过程中可能会出现脱层,这将影响圆柱壳的承载能力,因此,建立正确的分析模型来研究脱层壳的承载能力是非常有必要的。首先将含任意位置环向贯穿脱层的轴压圆柱壳分成多段子壳,用厚度的三次多项式和环向的三角级数模拟脱层壳屈曲时子壳的轴向和环向位移;然后利用变分原理导出了脱层壳的屈曲方程和定解条件;最后,将控制方程和定解条件写成状态空间形式并在轴向用状态空间方法进行求解。     

含脱层纤维增强复合材料层合板在湿热环境下的屈曲分析

依据复合材料细观力学研究了含脱层的正交各向异性复合材料层合板的力学性能与温度和湿度的关系,在宏-细观力学模型框架下建立了考虑湿热效应的屈曲控制方程,利用空间上分离变量的方法求解了控制方程,得到满足连续性条件和边界条件的控制方程的解。通过含脱层的复合材料层合板的屈曲数值算例,综合讨论了几何参数、材料参数和湿热环境等多方面的参数变化对含脱层的正交对称铺设复合材料层合板的临界屈曲载荷的 影响。     

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。     

轴向碰撞弹性直杆动力后屈曲有限元分析

利用显式动力学有限元方法对弹性直杆的动力后屈曲进行了分析;模拟了弹性直杆轴向碰撞动力屈曲的变形及发展过程。分析中将碰撞杆视为无初始缺陷的理想直杆,将弹性直杆动力屈曲双特征参数的解答作为非线性动力后屈曲求解的初始条件,实现了对无缺陷理想直杆的动力后屈曲分析。计算结果与文献中的实验数据获得了很好的一致。计算结果同时也揭示了直杆动力屈曲变形发展的机理,以及轴向应力波和屈曲变形的相互作用规律。     

应力波作用下弹性直杆动力分叉屈曲研究

对弹性直杆在应力波作用下动力分叉屈曲进行分析与探讨,提出求解应力波作用下直杆动力屈曲数值方法。该方法统一双特征参数法与最优模态法思想,可用于解决时变动载荷作用下屈曲问题,且对阶跃载荷及时变动载荷引起的应力波作用下屈曲问题具有统一屈曲判别形式,与实验数据对比表明该方法准确、可行。     

含内埋矩形脱层板屈曲分析的传递函数方法

研究了含任意内埋矩形脱层复合材料层合板的屈曲问题。采用一种基于Mindlin一阶剪切理论的条形传递函数方法,将含内埋矩形脱层的复合材料层合板分成含脱层和不含脱层的两种矩形超级单元,然后由各超级单元之间连接结点处的位移连续和力平衡条件得到脱层板屈曲的特征方程,进而得到脱层板的屈曲载荷和屈曲模态。进行参数分析发现,脱层大小、深度、位置以及脱层板的边界条件和复合材料铺层方向对脱层板屈曲载荷的影响较显著。     

弹性压应力波下直杆分叉动力失稳特征值有限元分析

运用有限元特征值分析方法对弹性压应力波作用下直杆分叉动力失稳问题进行了研究。基于应力波理论和相邻平衡准则导出了直杆动力失稳时的有限元特征方程,把弹性直杆的动力失稳问题归结为特征值问题。通过引入直杆动力失稳时的波前约束条件实现了此类问题的有限元特征值解法。     

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.     

Buckling of composite plates by global–local plate theory

The bifurcation buckling problem of laminated composite plates is formulated within the framework of a multilength scale plate theory. This theory is a combination of single-layer and layer-wise theories. It is generated by representing the displacement as the sum of global and local effects that introduce a coupling between the two length scales.Comparisons between the presently predicted buckling loads of homogeneous and orthotropic laminated plates and the exact solutions show a very good correlation. Furthermore, the theory accurately predicts the buckling load of symmetric cross-ply plates as compared with the results of a layer-wise approach. This accuracy is achieved with reduced computation expense.The global–local plate theory is general enough to incorporate delamination effects. As a result of the inclusion of these effects, the buckling loads of plates with imperfect interlaminar bonding are predicted.     

Numerical analysis of delamination buckling and growth in slender laminated composite using cohesive element method

In this article, the finite element method (FEM) using cohesive element is applied to predict the delamination buckling and growth in slender laminated composite with embedded delamination under compressive load. In particular, the study is focused on the significant effects of delamination buckling for various parameters in slender composite laminate, such as model length–width ratio, delamination shape, delamination size, and delamination depth position. Furthermore, the delamination growth is assessed to investigate the influence of some key parameters (delamination size and delamination depth position) on the delamination growth load, growth shape and direction.     

基于弯曲刚度最大分层临界载荷的层压板局部屈曲预测

提出了一种预测含特定分层损伤层压板发生局部屈曲时整体应变的方法。认为含分层子板的局部屈曲载荷由其弯曲刚度最大的分层决定, 因而含有相同最大弯曲刚度分层的不同子板具有相同的屈曲载荷。在已知弯曲刚度最大分层的屈曲载荷的情况下, 根据层压板的轴向刚度公式, 计算出发生局部屈曲时弯曲刚度最大的分层与完好的基板分别承受的载荷, 即得到总载荷, 进而得到层压板的整体应变。用ABAQUS有限元分析软件建立含分层损伤的层压板模型, 使用准静态加载进行了多种分层深度和分层位置下的局部屈曲仿真, 所得局部屈曲载荷符合上述推论。用所提方法预测发生局部屈曲时的整体应变, 结果与有限元结果吻合较好, 此方法可用于建立分层参数识别的参照样本库。     

Stability analysis of delaminated composite beams

This study describes the dynamic stability of composite cantilever beams subjected to periodic axial loading with delaminations at pre-set locations. A computer code based on the finite element method is developed to calculate the natural frequencies, critical buckling loads and dynamic instability regions of the woven and laminated composite beams with different stacking sequences ([0]₄, [0/90]_s and [90]₄), corresponding to this peculiar delamination case. The results of the developed code for the natural frequencies are compared with the natural frequencies obtained experimentally and numerically with commercial FEA (ANSYS). The critical buckling loads are also compared with the ones obtained from ANSYS simulations.     

双参数冲击荷载作用下弹性压杆的动力屈曲研究

作用在实际结构上的冲击荷载往往是相当复杂的,冲击荷载形式对结构动力屈曲有较大影响。对双参数冲击荷载作用下的弹性压杆动力屈曲进行研究,采用等价矩形脉冲对荷载进行简化。分别对理想的和初始几何缺陷的弹性压杆冲击屈曲进行分析和计算,并以两端简支和两端固定轴心压杆冲击屈曲作为算例,初步揭示了冲击荷载形式对轴心压杆动力屈曲的影响规律,获得了有价值的结论。     

A higher order plate theory for dynamic stability analysis of delaminated composite plates

A higher order shear deformation theory is used to investigate the instability associated with delaminated composite plates subject to dynamic loads. Both transverse shear and rotary inertia effects are taken into account. The procedure is implemented using the finite element method. Delamination is modeled using the penalty parameter approach. The natural frequencies are computed and compared with NASTRAN 3D results and available experimental data. The effect of delamination on the critical buckling load and the first two instability regions is investigated for various loading conditions, plate thickness and boundary conditions. As expected the natural frequencies and the critical buckling load of the delaminated plate are lower than those of the nondelaminated plate. They decrease with increase in delamination length. Increase in delamination length causes instability regions to be shifted to lower parametric resonance frequencies and the normalized width of the instability regions to increase.     

含椭圆分层损伤复合材料层合板分层前缘接触效应研究

采用基于Mindlin 一阶剪切理论的四节点板单元, 分析了分层前缘闭合接触效应对含椭圆分层复合材料层合板前后屈曲行为的影响。通过在分层区域内引入虚杆单元来防止上、下子板发生相互重叠, 并假设接触区内没有摩擦。结果表明, 分层前缘的闭合接触效应受分层几何形状的影响很大, 当椭圆分层子板的长轴与压缩载荷方向一致时, 闭合接触效应对含分层层合板前后屈曲行为最大。