Evaluation of the Wedge Cleavage Test for Assessment of Durability of Adhesive Bonded Joints.

The Boeing wedge test was applied to joints of aluminium alloy made with three adhesives differing widely in toughness. Bonding pretreatments chromicsulphuric acid pickle, chromic acid anodise and wet alumina grit blast were compared for two of the adhesives, and clear differences in crack length appeared after exposure to 50 C and 96 r.h. Rates of crack growth were determined in both ambient and warm humid environments, and suitable times are suggested for measurement of crack length. Wedge driving speed can affect results and should be standardised. Results are more informative if shown as fracture energies rather than crack lengths, and the approximations involved are discussed. Practical aspects of the test are described and possible errors quantified. Fracture energies typically showed coefficients of variation of 5-20.