Tapered Double Cantilever Beam Fracture Tests of Phenolic-Wood Adhesive Joints: Part II. Effects of Surface Roughness, the Nature of Surface Roughness, and Surface Aging on Joint Fracture Energy

Robert O. Ebewele, Bryan H. River, James A. Koutsky

Abstract


Tapered double cantilever beam specimens were used to test the effect of surface roughness, the nature of surface roughness, and surface aging on the fracture energy of phenolic-wood adhesive joints. The fracture energy and the failure characteristics of the joints were found to depend not only on the surface roughness but also on the method of surface preparation. The fracture energy increased monotonically with surface roughness for specimens derived from hand-sanded surfaces but exhibited a minimum for specimens obtained from machine-sanded surfaces. Generally, joints from hand-sanded surfaces had higher fracture energies than those derived from the machine-sanded surfaces. Within the joints derived from the machine-sanded surfaces, those sanded perpendicular to the direction of crack growth had higher fracture energies than those sanded parallel to the direction of crack growth. Aging surfaces prior to bonding significantly decreased adhesive joint strength.

Notwithstanding the differences in roughness, microscopic examination revealed little difference in the appearance of the sanded surfaces. Adhesive did not penetrate hand-sanded surfaces to any appreciable extent, but did deeply penetrate both the vessel and fiber lumens on the machine-sanded surfaces. Microscopic examination of the fractured surfaces did reveal significant differences that related to the fracture toughness of the bond.


Keywords


Tapered double cantilever beam;fracture energy;adhesive joints;phenol-resorcinol;surface roughness;adhesive penetration

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