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2 2022

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Damage to inverse hybrid laminate structures: an analysis of shear strength test

Frankiewicz Mariusz, Ziółkowski Grzegorz, Dziedzic Robert, Osiecki Tomasz, Scholz Peter

Materials Science Poland

2022

Vol. 40, No. 1

130--144

Hybrid laminates with continuous fiber reinforcement, such as glass reinforced aluminium laminate (GLARE), aramid reinforced aluminum laminate (ARALL), or carbon reinforced aluminum laminate (CARALL), have been developed to increase the lightweight potential and fatigue resistance applied for aircraft structures. However, the use of thermosetting matrices imposes material limitations regarding recycling, malleability, and manufacturing-cycle times. The inverse hybrid laminate approach is based on a continuous fiber-reinforced thermoplastic matrix, in which a metal insert is integrated. For efficient manufacturing of the novel composites in high-volume production processes, conventional sheet metal–forming methods have been applied. It helped to reduce the cycle times and the costs of the forming equipment compared to currently used hybrid laminate-processing technologies. The present study analyzes the damage to the inverse hybrid laminate structures resulting from the interlaminar shear strength test. The tests were performed for eight laminate material configurations, which differed by the type and directions of the reinforced glass and carbon fibers in the polyamide matrix and the number of the fiber-reinforced polymer (FRP) layers in the laminates. Industrial computed tomography and scanning electron microscopy were used for analysis. Observed damages, including fiber–matrix debonding, fiber breakages, matrix fractures, interfacial debonding, and delamination in selected areas of the material, are strictly dependent on the laminate configurations. FRP layers reinforced by fibers perpendicular to the bending axis presented better resistance against fractures of the matrix, but their adhesion to the aluminum inserts was lower than in layers reinforced by fibers parallel to the bending axis.

The Influence of Material Configuration of Fibre-Metal Laminates with Alumina Core on Flexural Strength

Frankiewicz Mariusz, Karoluk Michał, Dziedzic Robert, Timmel Tristan, Scholz Peter

Fatigue of Aircraft Structures

2022

Iss. 14

18--28

Fibre metal laminates (FMLs) consisting of layers made of PA6 polyamide prepregs reinforced with glass and carbon fibres and an aluminium alloy core are the new variant of the other types used by aerospace FML materials such as GLARE or CARALL. By using a thermoplastic matrix, they can be shaped by stamping processes, which allows for a more efficient production process than classical laminating methods such as vacuum bagging. In addition to the improved impact energy absorption efficiency, the metallic core can be utilised to effectively bond the composite part to adjacent metallic structures. This article presents the influence of the material configuration of fibre-metal laminates consisting of continuous fibre-reinforced thermoplastic outer layers integrated with a layer of metallic aluminium alloy inserts - a number of layers, type and direction of reinforcing fibres - on the static and fatigue flexural properties. In this study, eight laminate configurations were prepared using a one-step variothermal consolidation process. The results showed that in the three-point flexural fatigue test, the samples exceeded 106 cycles at stresses <30% of the static bending strength. Laminates with predominantly longitudinally reinforced layers showed the highest fatigue strength among the FML samples analysed. The type of reinforcing fibres and the number of layers were less affected on the analysed mechanical properties.