Development and Testing of Woven FRP Flexure Hinges for Pressure-Actuated Cellular Structures with Regard to Morphing Wing Applications

Abstract

Shape-variable structures can change their geometry in a targeted way and thus adapt their outer shape to different operating conditions. The potential applications in aviation are manifold and far-reaching. The substitution of conventional flaps in high-lift systems or even the deformation of entire wing profiles is conceivable. All morphing approaches have to deal with the same challenge: A conflict between minimizing actuating forces on the one hand, and maximizing structural deflections and resistance to external forces on the other. A promising concept of shape variability to face this challenging conflict is found in biology. Pressure-actuated cellular structures (PACS) are based on the movement of nastic plants. Firstly, a brief review of the holistic design approach of PACS is presented. The aim of the following study is to investigate manufacturing possibilities for woven flexure hinges in closed cellular structures. Weaving trials are first performed on the material level and finally on a five-cell PACS cantilever. The overall feasibility of woven fiber reinforced plastics (FRP)-PACS is proven. However, the results show that the materials selection in the weaving process substantially influences the mechanical behavior of flexure hinges. Thus, the optimization of manufacturing parameters is a key factor for the realization of woven FRP-PACS.

Transient Dynamic System Behavior of Pressure Actuated Cellular Structures in a Morphing Wing

“…An extended calculation approach that is presented by Pagitz et al further increases the prediction accuracy by taking the cell wall compliance into account [39]. The subject of the current work is the design of flexure hinges considering manufacturing constraints that are specific to automated textile fabrication [34]. Based on these findings, an improved modeling approach can be implemented to account for the hinge transition geometry.…”

“…This material is selected inside the group of FRP based on three reasons: (1) glass-fibers have a relatively high elongation at break and they are considerably less sensitive to compression than carbon or aramid fibers. Both is beneficial for the application as highly deflected flexure hinges; (2) the development of an automated manufacturing process for PACS made out of woven GFRP is part of a current research project [34]; and, (3) the usability of HexPly913 in the context of PACS has already been proven during the realization of the first functional demonstrator [25].…”

Thermoplastic Composites for Integrally Woven Pressure Actuated Cellular Structures: Design Approach and Material Investigation

“…The overall stiffness of the PACS is adjusted via the thickness of the cell walls. For a secure closure [ 26 ], the cell walls should simultaneously be used for screwing on appropriate closure caps. These can be realized by weaving-integrated inserts or screws directly inserted into the composite.…”

“…The purely weaving implementation of such thicknesses is not reasonable. Nevertheless, in order to represent such wall thicknesses, different strategies are available, including monolithic composite using composite inserts [ 25 , 26 ], sandwich, or hollow chamber structure. The selection was made considering the results of the numerical evaluation of the deformation behavior.…”

“…The results from the reduced-order truss model were compared with the FEA results for the two cross-sectional designs “CS-AM” and “CS-FRP”. Differences between the reduced-order truss model and the FEA on the design “CS-AM” have already been explained in [ 26 ] and arise primarily from the simplification in the reduced-order model. The hinge transition areas were not taken into account and the deformation of the cell walls was neglected, both resulting in lower deflections, compared to the FEA.…”