Flexural Behavior of Sandwich Panels with Bio-FRP Skins Made of Flax Fibers and Epoxidized Pine-Oil Resin

Structural sandwich panels with fiber-reinforced polymer (FRP) skins are becoming an increasingly popular system because of their remarkable light weight, ease and speed of installation, and high thermal insulation capabilities. This paper looks into the potential for replacing conventional glass fiber-reinforced polymer (GFRP) skins with bio-based skins made of unidirectional flax fibers and a resin blend consisting of epoxidized pine oil. A comprehensive material testing program was first carried out on 70 standard tension and compression coupons. Then, 36 sandwich panels of 1,000 x 150 x 75 mm were tested under four-point loading. The number of flax fiber-reinforced polymer layers of skin was varied from one to five [in comparison to one layer of GFRP, an epoxidized pine oil resin blend to epoxy, and the wet layup (WL) fabrication method to vacuum bag molding]. Sandwich panels with three layers of flax fibers provided equivalent strength and stiffness, but better deformability, compared to panels with one layer of glass fibers. Epoxidized pine oil-based skins decreased strength by up to 23% compared to epoxy-based skins. Vacuum-bagged panels decreased strength by up to 27% compared to WL as a result of thinner skins. As the number of flax layers increased from one to five, failure modes transitioned from skin wrinkling in the constant moment region to core shear failure or compression skin crushing in the shear span. (C) 2015 American Society of Civil Engineers.