Free-edge effects in curved composite laminates: analysis, optimization and test

在许多应用情况下，由于曲率引起的层间剥离应力引发的分层导致弯曲层合结构失效。此外，在层合复合材料结构中，局部和潜在的奇异应力场出现在自由层合板边缘附近，这增加了复合材料层合板的分层临界性。到目前为止，只有纯粹的数值分析方法可以用来评估弯曲层合结构中的自由边缘应力场。因此，本研究计划致力于发展用于分析弯曲复合材料层合板自由边缘效应的封闭形式解析和半解析方法。封闭形式的解析近似方法可以通过使用各种策略来开发，其中以分层力和力矩形式评估应力结果是最简单和直接的方法。此外，也可以采用所谓的力平衡法形式的分层应力方法。最后，它打算使用基于分层位移的分析方法。所有的分析方法都将通过比较有限元模拟来验证。此外，所有的分析方法将通过实验结果进行验证。一旦近似闭型解析方法建立，弯曲层合结构中的自由边效应将被视为一个优化问题。通过使用数学规划的方法，将探索在弯曲层合结构的情况下可以利用哪种优化潜力，以及自由边缘效应是否可以最小化。开发的分析方法的质量和优化程序的结果将通过对弯曲层压板试样进行测试来评估。

In many application cases, curved laminated structures fail by delaminations which are triggered by interlaminar peeling stresses that arise due to the curvature. Further, in laminated composite struc-tures localized and potentially singular stress fields arise in the vicinity of the free laminate edges which add to the delamination criticality of a composite laminate. As of today there are only purely numerical means of analysis available by which free-edge stress fields in curved laminated struc-tures can be assessed. Consequently, this research proposal is devoted to the development of closed-form analytical and semi-analytical methods for the analysis of free-edge effects in curved composite laminates. Closed-form analytical approximate methods can be developed by using various strategies where the assessment of stress resultants in the form of layerwise delamination forces and moments is the most simple and straightforward one. Furthermore, layerwise stress based approaches in the form of the so-called force-balance-method can be employed as well. Lastly, it is intended to use layerwise displacement based analysis approaches. All analysis methods will be verified by comparative finite element simulations. Furthermore, all analysis methods will be validated by means of experimental results. As soon as approximate closed-form analytical methods have been established, the free-edge effect in curved laminated will be considered as an optimization problem. By using the methods of mathematical programming it will be explored which optimization potential can be exploited in the case of curved laminated structures and if free-edge effects can be minimized. The quality of the developed analysis approaches and the results of the optimization procedures will be assessed by tests performed on specimens of curved laminates.