Buckling, Postbuckling and Stress Concentration Problems of Stiffened Composite-Panels

加筋复合板的屈曲、后屈曲和应力集中问题

• 批准号: 426146527
• 负责人: Professor Dr.-Ing. Christian Mittelstedt
• 金额: --
• 依托单位: Fachgebiet Konstruktiver Leichtbau und Bauweisen
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/426146527?language=en
• 关键词: Buckling; Postbuckling; Stress; Concentration; Problems

Traditional metallic lightweight constructions are increasingly replaced by composite laminated structures. When analyzing and designing thin-walled laminated structures, the stability behavior is a predominant factor to be considered. This project is devoted to the development of according efficient and yet highly accurate analysis methods and is divided into three consecutive and inter-dependent research topics:Research topic 1:When designing the stiffeners of a stiffened thin-walled structure, it is an important criterion to pre-vent global buckling modes. Hence, the concept of the so-called minimum stiffness is employed, i.e. the determination of the elastic properties of the stiffeners in such a way that a local buckling mode is enforced. The state of the art concerning stiffened composite panels is scarce, and especially with respect to the application of shear deformation theories there are no investigations available. This project thus employs higher-order laminate theories and energy based analysis methods for the solution of the minimum stiffness problem of composite structures. Research topic 2:Stiffened panels can sustain loads beyond the critical local buckling load so that it is imperative to operate lightweight structures in the postbuckling range. For practical application purposes, closed-form analytical methods are the methods of choice due to their favorable computational efficiency. Given that the minimum stiffness requirements are fulfilled, the current research topic then focusses on the closed-form analytical treatment of the postbuckling behavior using adequate shape functions for all postbuckling degrees of freedom in conjunction with energy based analysis approaches, thus enabling the study of important postbuckling state variables such as the effective width. Research topic 3:Whenever a stiffened panel is operated in the postbuckling range, it is of utmost importance to de-termine the ultimate load carrying capacity. In the majority of cases of stiffened composite structures, the ultimate load is reached when delaminations in the vicinity of stiffener feet occur and grow in an unstable manner in the interface between panel and stiffener. The onset of delamination is triggered by the geometric discontinuity at the stiffener-panel junction and the according three-dimensional and potentially singular stress fields. Especially the interlaminar stresses play a crucial role in the onset of delaminations since these stresses act in a plane perpendicular to the fiber directions of the laminate layers. It is thus the aim to develop practically applicable analysis methods by which an efficient and reliable determination of these interlaminar stresses in the vicinity of the stiffener-panel junction is enabled. These investigations will include the development of a semi-analytical approximate method that is based on a layerwise laminate theory.

传统的金属轻量级结构越来越多地被复合层压结构所取代。在分析和设计薄壁的层压结构时，稳定性行为是要考虑的主要因素。该项目致力于开发有效但又高度准确的分析方法，并分为三个连续且相互依赖的研究主题：研究主题1：设计僵硬的薄壁结构的加强剂时，它是一个重要的标准预防全球屈曲模式。因此，采用了所谓的最小刚度的概念，即确定加强剂的弹性特性，以实施局部屈曲模式。关于僵硬的复合面板的最新技术很少，尤其是在剪切变形理论的应用方面，没有可用的研究。因此，该项目采用高阶层压理论和基于能量的分析方法来解决复合结构的最小刚度问题。研究主题2：僵硬的面板可以维持超出关键的本地屈曲负荷的负载，因此必须在弯曲后范围内操作轻量级结构。出于实际的应用目的，封闭形式的分析方法是由于其有利的计算效率而选择的方法。鉴于满足了最低刚度的要求，因此当前的研究主题将重点放在使用基于能量的分析方法结合使用的所有后弯曲自由度的适当形状功能上对后扣行为的封闭形式分析治疗，从而实现重要的研究后状态变量，例如有效宽度。研究主题3：每当一个僵硬的面板在后扎范围内运行时，脱离最终负载承载能力至关重要。在大多数僵硬的复合结构的情况下，当出现加性脚附近的分层时，达到了最终负载，并且在面板和加劲柜之间的界面中以不稳定的方式生长。分层的开始是由加强板连接处的几何不连续性以及根据三维且潜在的奇异应力场引发的。尤其是层间应力在分层的发作中起着至关重要的作用，因为这些应力作用于垂直于层压层层的纤维方向的平面。因此，它的目的是开发实际适用的分析方法，通过这种分析方法，通过这种分析方法，可以通过这种方法对加强板式交界处附近这些层间应力的有效和可靠的确定。这些研究将包括基于层次层压理论的半分析近似方法的发展。