An investigation on the flexural properties of balsa and polymer foam core sandwich structures: Influence of core type and contour finishing options

Abstract

Polymer foams are frequently used as core materials in sandwich structures for applications such as aerospace, naval, and wind industry. It is known that the core material contributes to the overall mechanical properties of these sandwich structures up to a remarkable extent. In addition, due to the curvature and geometrical complexities of several applications, these cores are available with special cuts/grooves (finishing options) to provide bendability and better resin infusion during processing. The goal of this study is to investigate the mechanical performance of synthetic polymer foams as core materials for sandwich structures. Balsa wood, which is the most common traditional structural core, was used as reference material. Glass fiber reinforced epoxy was employed as face sheets. End-grain Balsa wood, commercially available polyvinyl chloride and polyethylene terephthalate, and experimental grades of polyurethane foams were chosen as alternative core materials. Quasi-static flexural tests were carried out using a four-point bending setup according to ASTM C 393. Sandwich properties such as stiffness, core shear strength, and energy absorption were determined and compared. The contour cuts filled with resin show a reinforcing effect against transverse shear stresses leading to higher shear strengths. Digital image correlation was used to study the yielding and permanent strain of the foam core sandwich beams.

Mechanical properties of multifunctional foam core materials

“…PET foams are becoming more attractive as sandwich core materials due to some key advantages and therefore could compete with more traditional foams of PVC, PU, and PS [54]. Although PET foams could possess good fatigue resistance [67], their static strength and moduli are usually lower than those of PVC foams at comparable densities. In addition, PET foam cores can be thermally bonded to thermoplastic face sheets to make full thermoplastic sandwich structures with improved impact properties.…”

“…There are a few works [13,[67][68][69], though, which make correlations between foam cell structure and the resulting compression and shear properties. There are a few works [13,[67][68][69], though, which make correlations between foam cell structure and the resulting compression and shear properties.…”

Quasi-static and fatigue properties of a balsa cored sandwich structure with thermoplastic skins reinforced by flax fibres

“…One of its main advantages is its ability to absorb energy. Balsa wood is also among the most frequently studied bio-based cores due to its high specific compressive and shear properties [10][11][12]. It has often been used in marine applications reinforced with GFRP [13].…”

Effects of the core density on the quasi-static flexural and ballistic performance of fibre-composite skin/foam-core sandwich structures

“…The deformation and failure characteristics of the foam core play a very important role in determining the mechanical performance of the sandwich structure. Hence, many research studies [9][10][11][12][13][14][15][16][17][18] have explored new types of sandwich structures by changing the type and density of the material used for the core.…”

“…Juntikka and Hallstrom [12] reported that the shear modulus, shear strength and shear strain at failure of sandwich structures were all affected by the choice of the density for the core material. Fathi et al [13,14] investigated the effect of the type of core material employed on the flexural properties of the sandwich structure for four different core materials made from PVC, poly(ethylene terephthalate) (PET), polyurethane (PU) and balsa wood, with skins of GFRP. All of these different types of sandwich structures were evaluated under four-point bend loading and it was found that the balsa-wood core imparted the highest shear strength.…”