The effect of elevated temperature on the mechanical properties and failure modes of GFRP face sheets and PET foam cored sandwich beams

Abstract

The influence of elevated temperatures on stiffness and strength of composite face sheet and polyethylene terephthalate foam cored sandwich beam has been experimentally investigated. Standard test methods and analytical failure models were used to determine the effect of elevated temperatures. The authors examined E-glass/epoxy cross-ply face laminates, polyethylene terephthalate foam, and sandwich beams consisting of glass/epoxy face laminates and polyethylene terephthalate foam core loaded in four-point flexure. The tensile properties of the face laminate were examined over a temperature range from 25 to 175°C. Compression and shear tests on the face laminate, polyethylene terephthalate foam, and sandwich beams were performed at temperatures up to 100°C. The face laminates exhibited moderate reductions of Young’s modulus and tensile strength, while the compressive strength, shear modulus, and shear strength substantially decreased at elevated temperatures. Similarly, the compressive and shear moduli as well as the compressive strength of the polyethylene terephthalate foam decreased substantially by exposure to a temperature of 100°C. The failure mode of the sandwich panels was observed to be highly dependent on temperature, distinguishing three basic failure modes, viz. core shear failure, indentation failure, and face wrinkling. The failure loads associated to these failure modes were calculated using models available in the literature. The failure loads were found to be consistent with the failure predictions and failure modes.

Mechanical behaviour in shear and compression of polyurethane foam at elevated temperature

“…Iosipescu and modified Arcan rig test methods, used in [7,11]) or (ii) the influence of combined stresses preventing the occurrence of 'pure' shear failure (e.g. bending tests, used in [9]).…”

“…strength and stiffness) occur [4]. Despite its scientific and practical relevance, few studies are available in the literature concerning the effects of elevated temperature on the shear [7,[9][10][11] and compressive [12][13][14][15][16] properties of polymeric foams used as core materials in sandwich construction.…”

“…In what concerns the investigation of the shear properties of polymeric foams at elevated temperatures (the most relevant mechanical properties for sandwich panels in bending), the following limitations were found in the literature: (i) in some studies ( [9,10]) the shear properties of the core materials were derived from sandwich specimens subjected to bendingthat is, the core was not subjected to a pure shear stress state (but also to bending and flatwise stresses); (ii) the lack of representativeness of foam core specimens regarding real full-scale sandwich constructions, due to their very small dimension ( [7,11]); (iii) in other studies, it was not possible to determine the shear strength at elevated temperature, because shear failure was not observed (due to limitations of the test setup [7,9] or the occurrence of different failure modes [9]). Additionally, very limited information is available for PUR foam, although it is very often used in civil sandwich applicationsno comprehensive studies were found about the influence of elevated temperature on its shear strength and compressive properties.…”

Effects of temperature and thermal cycles on the mechanical properties of expanded polystyrene foam

“…In the experimental work of Ref. 17, it was shown that the elastic and shear moduli of polyethylene terephthalate foam core decreased significantly (up to 40%). Reddy et al 18 found a significant reduction in the strength of Polyurethane foam after its exposure to hygrothermal conditions (40°C and 90% humidity).…”

“…The effects of high temperature on other polymer foams were investigated by Rezaei et al 17 Reddy et al, 18 Zhang et al, 19 Mazzuca et al, 20 and others. Small sandwich specimens are typically used in such investigations because testing the foam by itself under various loadings including tension and shear is very difficult to conduct.…”