Specific bending stiffness of in-mould-assembled hybrid sandwich structures with carbon fibre reinforced polymer face sheets and aluminium foam cores manufactured by a polyurethane-spraying process

Abstract

In this paper, the bending stiffness-to-weight-ratio of novel hybrid sandwich structures is investigated. The build-up of the sandwich panels consisted of face sheets made from carbon fibre reinforced polymer, aluminium foam cores and an interface of foamed polyurethane. The sandwich panels were produced in a single step, infiltrating the face sheet fibres and connecting the face sheets to the core simultaneously. By means of mechanical characterization, specimens with several variations of face sheet architecture and thickness, core structure and interface properties were examined. Quasi-static four-point bending and flatwise compression tests of the sandwich composites were conducted, as well as tensile tests of the face sheets. The results of the tensile and compressive tests were integrated in analytical models, describing the sandwich stiffness depending on the load case and the face sheet volume fraction. The effective Young’s modulus of the composite, measured in the four-point bending test, correlates well to the modelled effective bending modulus calculated from the single components face sheet and core. The model underestimates the effective density of the bending specimens. It could be shown that this underestimation results from the polyurethane foam connecting the face sheets to the core, as the mass of this polyurethane is not included in the model.

Low-Velocity Impact Properties of Sandwich Structures with Aluminum Foam Cores and CFRP Face Sheets

“…The configuration with less PUR (320w75oc, blue curve) shows a similar behavior as the standard configuration. This indicates that a large PUR quantity stiffens the core in terms of indentation rigidity-an effect not observable in quasi-static compression testing of the described materials [22].…”

“…The sandwich structures were produced using a modified PUR spraying process. Both the material combinations and the production process are also described in earlier publications by the authors [21][22][23]; however, all necessary information for the low-velocity impact properties are given here.…”

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

“…Some of the material systems used for this contribution have been investigated regarding stiffness properties in an earlier publication by the authors [25]. In the interests of clarity, all necessary information regarding the materials investigated in [25] are presented in the contribution at hand, including additional parameters and methods, which had not been previously described.…”

“…(a) CC “Alcoras,” (b) BCC “Alcoras,” (c) OC foam by m-pore, and (d) NH “ECA 9.6-48”. (a), (c), and (d) are corresponding to [25]. CC: closed-cell foam; BCC: blasted closed-cell foam; OC: open-cell foam; NH: Nomex honeycomb.…”

“…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].…”