Cost efficient manufacturing and design of sandwich structures with a polymethacrylimid foam core

Aramid paper or aluminium honeycomb cores are commonly used in sandwich structures in the field of aeronautical industry. However, production methods for those, especially the autoclave process, often require many consecutive process steps and therefore do not meet desired requirements in view of cycle time and costs. To develop a cost efficient design and manufacturing method that allows a considerable reduction of the production time and the productions steps it is necessary to develop a one-shot technology that does not require an autoclave. The vacuum infusion process, in particular the Membrane Assisted Resin Infusion (MARI), can significantly reduce those costs. A necessary requirement for this process is the usage of a core with closed cells to prevent unwanted penetration of resin into honeycomb cells. A polymethacrylimid (PMI) foam core represents a promising alternative. Structural relevant PMI foam cores that are close to airworthiness certification and enable good production results, come with a higher density at the same strength compared to e.g. honeycomb cores. This project aims to develop a methodology for the design and implementation of PMI foam cores in sandwich structures. To compensate for the high foam density, an optimized core structure has to be found. The design will be validated with a single aisle spoiler serving as a demonstrator. Two different simulation approaches are being pursued to obtain a lightweight foam structure. The first utilizes different subcomponents with optimized grid structures, to replace sections of the spoiler foam core, see Figure 1. The design of the subcomponent structures takes different load cases, relevant for aircraft spoilers, into account. To evaluate the behavior of the grid structures three-point bending simulations were performed and will be validated against experimental tests. For the second approach, regions with different foam core densities will be defined, depending on local mechanical loads and stresses, as schematically illustrated in Figure 2. Both approaches show promising results towards generating a design that is within the desirable weight tolerance while providing a sufficient strength, that allows for cost efficient manufacturing in a one-shot process. In a subsequent step, the two previous approaches might be combined to maximize the weight reduction. In addition to numerical (FE) simulations, an experimental test setup is used to demonstrate the technical feasibility of the two approaches for the entire spoiler.