Hollow structural parts made from fiber-reinforced plastics (FRP) which are used, for example, in a flap of an aircraft wing usually need complex metallic mandrels for their manufacturing. Due to changes in thickness as well as undercuts these metallic mandrels are usually built out of several individual parts in a very complex design, for easy demolding after manufacturing. A solution promising simplicity is the use of hollow FRP-cores which could stay in the component and carry structural loads. These so-called structural cores are being researched at IVW within the network program Next-Move. First off, the manufacturing-processes for structural cores are developed in RTM- as well as in Prepreg-Technology and later integrated in a structural aircraft component.
In a first step the manufacturing of structural cores takes place. For this, a customized bladder process is being developed. A unique part of this process is the draping directly on the bladder. The draped cores are placed in an existing tooling and supported with internal air pressure through a tube leading to the outside. Thereby different dimensions can be realized to offer lightweight solutions for varying applications.
For an optimal load transfer, the bonding between the structural cores and the structure is essential. For a maximized bonding strength the FRP-cores are cured to a defined degree of cure and then inserted in the structural component. Partial cure is carried out to produce cores with sufficient strength and at the same time guarantee a good bonding to the surrounding structure. Strength of the core is necessary for handling and integration purposes. Full cure of the structural cores then takes place in the following injection process together with the circumjacent structure. Bonding strength depends on the degree of cure and is higher for partially than for fully cured cores. Based on detailed investigations of the chemical reaction process and mechanical experiments of joining partners at different degrees of cure, the optimum configuration for the manufacturing process is defined. At the same time virtual parameter studies are conducted employing Finite Element Simulations for the stacking sequence and an optimized bonding. The results from experiments on coupon level are used thereby as input data. With help of simulation the realization of designs in components in varying geometries can be analyzed and their applicability benchmarked.
The joint project is funded by the German Federal Ministry of Economics and Energy as part of the aviation research program.
Dipl.-Ing. Thomas Rief
Institut für Verbundwerkstoffe GmbH
Telephone: +49 (0) 631/2017 415