Kappel, Andreas (2024)
On the computational modelling, global optimization and experimental investigation of the free-edge effect in composite laminated shells.
Technische Universität Darmstadt
Dissertation, Bibliographie

Kurzbeschreibung (Abstract)

With the objective of saving material and energy by minimizing the weight of designs, lightweight engineering has been referred to as a key technology in today's society. Given the background of exceptional specific properties, especially curved composite structures in the form of fibre-reinforced plastics exhibit a significant potential to maximize the efficiency and thus, meet certain life and reliability requirements of load-bearing components. However, due to the multilayered character, theoretically weak interlaminar stress singularities in the interfaces at the traction-free edges of composite laminated plates or shells are encountered which pose a significant challenge for the analysis and design of those structures. On the other hand, three-dimensional numerical simulations which account for such problems, are computationally inefficient. This becomes in particular critical during preliminary design studies and optimization runs wherein the same computations have to be repeated several hundreds or thousands of times in order to find a solution that fulfils the requirements. In view of the current demand, this contribution tries to make a significant impact on this research field by discussing the computational modelling, global optimization and experimental investigation of stress concentration phenomena in composite laminated shell panels undergoing hygro-thermo-mechanical loads. Following introductory remarks on the current state of science, two- and three-dimensional finite element models are developed in order to assess the validity and accuracy of the novel approximate analysis methods. In this context, a stress function approach is introduced which accounts for the computation of the state variables in thick, infinitely long composite laminated shell panels subjected to uniform edge loads, transverse loads on the inner and outer surface of the shell as well as arbitrary through-the-thickness hygro-thermal loads. The introduced closed-form analytical solution is then modified by means of a higher-order displacement-based layerwise approach. Herein, different discretization schemes are discussed, and the generalized governing equations are derived by virtue of the minimum total potential energy principle and the Euler-Lagrange equations. Based on the solution of the underlying boundary-value problem, the free-edge effect and the free-corner effect in composite laminated shell panels are investigated in detail. Thereafter, the introduced semi-analytical approach is utilized in order to minimize the delamination tendency of L-shaped CFRP and GFRP cross-ply laminated beams considering a four-point bending load and various restrictions. Finally, corresponding experimental investigations have been conducted in order to assess the validity and accuracy of the developed highly efficient approximate analysis methods.

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