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

• Applicant: Professor Dr.-Ing. Christian Mittelstedt
• Subject Area: Lightweight Construction, Textile Technology
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 427624054

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.

• DFG Programme: Research Grants