New Sandwich Structures Consisting of Aluminium Foam and Thermoplastic Hybrid Laminate Top Layers

Abstract

Sandwich structures consist of one light core layer and two top layers, which form the load-bearing structure. These layers have to be stiff and strong and have to protect the structure against indentations. The main task of the core layer is to keep the top layers in place and to generate a high shear stiffness. In order to obtain the required space between the top layers, the core layer has to have a high specific volume. Different sandwich materials with aluminium or steel top layers and cores of aluminium combs, corrugated aluminium sheets or aluminium foams are already known. In order to obtain better properties in terms of strength fibre-reinforced plastics (FRP) are utilised as top layers; this is the focus of numerous of the current research studies. The sole use of these materials leads to negative effects regarding the damage and impact behaviour. New top layers with high strength and high stiffness characteristics as well as good damage tolerances are to be expected by utilising metal layers in combination with endless fibre-reinforced plastics, so called hybrid laminates. These hybrid laminates combine the positive properties of metals (e.g. ductility) and fibre-reinforced plastics (e.g. tensile strength). The focus of this investigation lies on the production and characterisation of sandwich structures with aluminium foam core layers and hybrid laminate top layers. The foam cores consist of closed pore aluminium foams produced by utilising ingot and powder metallurgical techniques. The top layers consist of glass fibre-reinforced thermoplastics and aluminium layers. The production of the sandwich materials is realised by means of thermal pressing.

Sandwich Structures Consisting of Aluminum Foam Core and Fiber Reinforced Plastic Top Layers

“…Different ways of composite manufacturing were tested and compared according to DIN 53292: "testing of sandwiches; tensile test perpendicular to the faces". For the manufacturing of the sandwiches, the following approaches were investigated: 1) compression molding with heating of both components 2) compression molding with heating only the foam 3) compression molding with preheating by infrared 4) adhesive bonding without inducing heat (for comparison).…”

“…Later additional researches regarding the influences of fiber bridging by aramid fibers could be approached. In a previous study, Nestler et al [4] conducted investigations regarding the combination of even foam plates with thermoplastic composite sheets and hybrid laminates. This included the production and determination of the mechanical properties.…”

Failure mode maps for four-point-bending of hybrid sandwich structures with carbon fiber reinforced plastic face sheets and aluminum foam cores manufactured by a polyurethane spraying process

“…In crash events, honeycomb structures which are specifically aligned in (or even designed for) the crash direction can absorb energy, otherwise the failure is sudden [5]. Foam cores, especially made from metallic foams [4,12–24], can absorb energy without the need of alignment and induce “benign” failure [9]. As a downside, metal foams often possess a higher density, resulting in a slightly lower stiffness-to-weight-ratio [25].…”

“…Manufacturing sandwich panels usually requires a separate joining step to create the connection between face sheets and core using an adhesive film [8,20]. The elimination of this bonding step can be performed in various ways.…”

“…For the mechanical characterization of sandwich panels, three-point [5–10,12–19,30–33] and four-point [4,6,7,20–23,27,30] bending tests are common testing procedures. The failure of sandwich panels under bending load is induced by its weakest constituent, which is determined by the component properties and the loading conditions.…”