Adhesive Through-Reinforcement Improves the Fracture Toughness of a Laminated Birch Wood Composite

Wenchang He,Philip D Evans

doi:10.1155/2017/5637248

Abstract

In this paper we test the hypothesis that adhesive through-reinforcement in combination with glass-fibre reinforcement of adhesive bond lines will significantly improve the fracture toughness of a laminated birch wood composite. We test this hypothesis using a model composite consisting of perforated veneer that allowed a polyurethane adhesive to penetrate and reinforce veneers within the composite. Model composite specimens were tested for mode I fracture properties, and scanning electron microscopy was used to examine the microstructure of fracture surfaces. Our results clearly show that through-reinforcement, and also reinforcing adhesive bond lines with glass-fibre, significantly improved fracture toughness of the birch wood composite. Our results also indicate that improvements in fracture toughness depended on the level of reinforcement. Improvements in fracture toughness were related to the ability of the reinforcement to arrest crack development during fracture testing and the fibre bridging effect of glass-fibre in adhesive bond lines. We conclude that through-reinforcement is an effective way of improving the fracture toughness of laminated wood composites, but further research is needed to develop practical ways of creating such reinforcement in composites that more closely resemble commercial products.

Highlights

Fracture toughness is an indicator of the stress required to propagate a preexisting flaw and is a critical property for materials such as laminated composites used in demanding structural applications [1]
The addition of glassfibre to adhesive bond lines was more effective at improving the fracture toughness of the birch composite containing through-reinforcement than it was at improving the fracture toughness of the control
Our results support our hypothesis that introduction of through-reinforcement across veneers increases the fracture toughness of a laminated birch wood composite and show that improvements in fracture toughness depend on the level of reinforcement

Summary

Introduction

Fracture toughness is an indicator of the stress required to propagate a preexisting flaw and is a critical property for materials such as laminated composites used in demanding structural applications [1]. Delamination of laminated composites reduces their stiffness and strength and can lead to loss of structural integrity [2]. There is significant interest in improving the fracture toughness of laminated composites, those used for aircraft construction [1, 3]. The glue lines of plywood and other laminated wood composites such as laminated veneer lumber (LVL) and glue-laminated lumber (glulam) often contain flaws and they can fail by delamination [7]. There has been interest in improving their fracture toughness [8]

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Conclusion