Explicit local buckling analysis and design of fiber–reinforced plastic composite structural shapes

Pultruded fiber–reinforced plastic (FRP) composite structural shapes (beams and columns) are thin-walled open or closed sections consisting of assemblies of flat plates and commonly made of E-glass fiber and either polyester or vinylester resins. Due to high strength-to-stiffness ratio of composites and thin-walled sectional geometry of FRP shapes, buckling is the most likely mode of failure before material failure. In this paper, explicit analyses of local buckling of rectangular orthotropic composite plates with various unloaded edge boundary conditions (i.e., (1) rotationally restrained along both unloaded edges (RR), and (2) one rotationally restrained and the other free along the unloaded edges (RF)) and subjected to uniform in-plane axial action at simply-supported loaded edges are first presented. A variational formulation of the Ritz method is used to establish an eigenvalue problem, and explicit solutions of plate local buckling coefficients in term of the rotational restraint stiffness (k) are obtained. The two cases of rotationally restrained plates (i.e., the RR and RF plates) are further treated as discrete plates of closed and open sections, and by considering the effect of elastic restraints at the joint connections of flanges and webs, the local buckling of different FRP shapes under uniform axial compression is studied. The approximate expressions of the rotational restraint stiffness (k) for various common FRP sections are provided, and their application to sectional local buckling predictions is illustrated. The explicit local buckling formulas of rotationally restrained plates are validated with the exact transcendental solutions. The analytical predictions for local buckling of various FRP profiles based on the present discrete plate analysis and considering the elastic restraints of the flange–web connections are in excellent agreements with available experimental results and finite element eigenvalue analyses. A design guideline for local buckling prediction and related performance improvement is proposed. The present explicit formulation can be applied effectively to determine the local buckling capacities of composite plates with elastic restraints along the unloaded edges and can be further used to predict the local buckling strength of FRP shapes.     

Bending and Stability of a Glued Curvilinear Rod with Initial Irregularities

A differential equation has been derived for the bending of a glued curvilinear rod with initial deflections of its elements. Adhesive joints work in shear. The 2D stability, collapse and buckling are investigated for a jointed rod, and the formulas are derived to determine the critical values of its element parameters. Some separate cases are considered and examples are given. __________ Translated from Problemy Prochnosti, No. 6, pp. 114 – 123, November – December, 2005.     

Thermal buckling of cross-ply laminated composite and sandwich plates according to a global higher-order deformation theory

A two-dimensional global higher-order deformation theory is presented for thermal buckling of cross-ply laminated composite and sandwich plates. By using the method of power series expansion of continuous displacement components, a set of fundamental governing equations which can take into account the effects of both transverse shear and normal stresses is derived through the principle of virtual work. Several sets of truncated Mth-order approximate theories are applied to solve the eigenvalue problems of a simply supported multilayered plate. Modal transverse shear and normal stresses can be calculated by integrating the three-dimensional equations of equilibrium in the thickness direction, and satisfying the continuity conditions at the interface between layers and stress boundary conditions at the external surfaces. Numerical results are compared with those of the published three-dimensional layerwise theory in which both in-plane and normal displacements are assumed to be C⁰ continuous in the continuity conditions at the interface between layers. Effects of the difference of displacement continuity conditions between the three-dimensional layerwise theory and the global higher-order theory are clarified in thermal buckling problems of multilayered composite plates.     

An Evaluation of Digital Image Correlation Criteria for Strain Mapping Applications

Abstract:  The performance of four digital image correlation criteria widely used in strain mapping applications has been critically examined using three sets of digital images with various whole-field deformation characteristics. The deformed images in these image sets are digitally modified to simulate the less-than-ideal image acquisition conditions in an actual experiment, such as variable brightness, contrast, uneven local lighting and blurring. The relative robustness, computational cost and reliability of each criterion are assessed for precision strain mapping applications. Recommendations are given for selecting a proper image correlation criterion to efficiently extract reliable deformation data from a given set of digital images.     

基体非线性对单向玻璃纤维增强复合材料压缩性能的影响

通过微观测试研究单向玻璃纤维增强复合材料(FRP)的纵向压缩破坏．并建立一个与纤维体积、基体和纤维的性质有关的模型来预测FRP的纵向压缩强度．实验中，设计了一个特殊加载装置用来放在Leitz光学仪器下观察压缩破坏过程，观察到一些纤维首先弯折，然后引起相邻纤维弯折系列响应，最后导致整个试件压缩破坏．强度预测与实验结果吻合较好，结果表明当纤维有微挠度特别是有微弯曲时，压缩强度与基体的非线性有关．     

Optimization of practical trusses with constraints on eigenfrequencies, displacements, stresses, and buckling

In this paper we consider the optimization of general 3D truss structures. The design variables are the cross-sections of the truss bars together with the joint coordinates, and are considered to be continuous variables. Using these design variables we simultaneously carry out size optimization (areas) and shape optimization (joint positions). Topology optimization (removal and introduction of bars) is only considered in the sense that bars of minimum cross-sectional area will have a negligible influence on the performance of the structure. The structures are subjected to multiple load cases and the objective of the optimizations is minimum mass with constraints on (possibly multiple) eigenfrequencies, displacements, and stresses. For the case of stress constraints, we deal differently with tensile and compressive stresses, for which we control buckling on the element level. The stress constraints are imposed in correlation with industrial standards, to make the optimized designs valuable from a practical point of view. The optimization problem is solved using SLP (Sequential Linear Programming).     

单层甲板屈曲时船体极限弯矩统计特征值的计算

传统的求单层板架临界应力的方法只能处理一些对称形式的板架，用有限地克服了这一局限，可以求解任意形式平面单层板架的临界应力，算例的比较和分析表明这种做法是合理可行的，以此为基础，按Ｒｏｓｅｎｂｌｕｅｔｈ法进行一些计算了体极限弯矩的统计值，并且分析了多个基本随机变量单独变异和共同变异对极经矩统计值的影响。     

导线对输电塔体系纵向振动的影响界限及简化抗震计算方法

根据作提出的纵向振动时高压输电塔体系的简化抗震计算模型，导出了一般振动方程，编制了高压输电塔体系抗震计算考虑导线影响的计算程序。经大量的输电塔体系地震反应分析，得出了导线的影响随跨度的增加而增大的结论。分析结果表明，按现行《电力设施抗震设施规范》设计的大跨越输电塔体系在强震作用下是偏于不安全的。最后，给出了输电塔体系纵向振动时考虑导线影响的界限，提出了输电塔-导线体系纵向振动的简化抗震计算方法：     

板状结构流致振动的研究

采用二维不可压缩无粘流体模型，探讨了板状结构的流致振动问题。发现板在两端简支、中点联结松动时，结构首先出现屈曲失稳，而不会发生颤振失稳。求得了具体结构参数情况下的第一阶屈曲临界流速，计算了结构参数变化对临界流速的影响。     

Al-Mg-Si基合金方板对角拉伸临界失稳及应力应变场模拟

基于弹塑性板壳失稳理论,采用虚功原理和非线性弹塑性有限元方法,模拟了Al-Mg-Si基合金方板对角拉伸的皱曲特性,得出了方板临界失稳的物理判据和临界状态下的应力、应变场.结果表明:Uz和εx急剧变化的突发点为起皱的失稳点,拉伸失稳的临界载荷为7780牛顿.拉伸载荷达临界载荷前表现为面内变形,达临界载倚时方板发生分叉失稳.继续拉伸,演变成起皱带.临界状态下横向应变和横向应力的分布不均匀,最大值都发生在方板中心.可把失稳状态下方板中心点的横向压应力作为描述YBT模型皱曲失稳的特征值.