Free-edge effects at circular holes in composite laminated structures

复合材料层合结构中圆孔处的自由边缘效应

• 批准号: 417731066
• 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
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/417731066?language=en
• 关键词: Free; edge; effects; circular; holes

Stress concentration problems in composite laminated structures such as the so-called free-edge effect consist of significant and potentially singular interlaminar stresses in the vicinity of free laminate edges which often leads to according failure modes such as edge delaminations. While the rather classical situation of a straight free laminate edge has been under scientific investigation for nearly 50 years, related stress concentration problems such as the free-edge effect at circular holes in composite laminates have been treated at much lesser depth. This project is devoted to the closed-form analytical and semi-analytical investigation of the free-edge effect in the vicinity of circular holes in plane composite laminated structures. Besides the rather straightforward determination of delamination forces and moments, several approximate layerwise analysis approaches shall be developed which can be subdivided into methods that work with adequate shape functions for the stresses and those that use layerwise approximations of the displacement field. A further analysis method that shall be employed is the so-called Boundary-Finite-Element-Method (BFEM) that uses a 2D discretization of the hole surface while in the radial direction semi-analytical formulations for all state variable can be derived from a variational principle. Consequently, the BFEM incorporates the distinct advantages of the Finite Element Method and the Boundary Element Method and thus is an attractive analysis approach for sophisticated stress concentration problems such as the free-edge effect. Lastly, the free-edge effect problem shall be transformed into an optimization problem by employing the means of the methods mathematical programming in order to clarify which optimization potential can be exploited when free-edge stresses at circular laminate holes are the focus of the investigations.

复合材料层合结构中的应力集中问题，如所谓的自由边缘效应，是指在层合板自由边缘附近存在显著的、潜在的奇异层间应力，这往往导致相应的失效模式，如边缘脱层。虽然相当经典的情况下，一个直的自由层合板边缘已经在科学研究了近50年，相关的应力集中问题，如在复合材料层合板中的圆孔的自由边缘效应已被处理在更小的深度。本计画致力于平面复合材料层合结构圆孔附近自由边效应之解析与半解析研究。除了相当直接地确定脱层力和脱层力矩外，还应开发几种近似的分层分析方法，这些方法可细分为使用适当的应力形状函数的方法和使用位移场的分层近似的方法。应采用的另一种分析方法是所谓的边界有限元法（BFEM），其使用孔表面的2D离散化，而在径向方向上，所有状态变量的半解析公式可以从变分原理导出。因此，边界有限元法结合了有限元法和边界元法的独特优点，因此是一个有吸引力的分析方法，复杂的应力集中问题，如自由边缘效应。最后，利用数学规划的方法，将自由边效应问题转化为优化问题，以阐明当层合板圆孔处的自由边应力为研究重点时，可以利用何种优化潜力。