Prévoir la durée de vie d’un adhésif dans un environnement agressif

L’utilisation du “test coin”

Use of the “wedge-test” to estimate the lifetime of an adhesive joint in agressive environment

Chef de groupe chimie - Société ASULAB SA.

Abstract

The “Boeing wedge-test” is often used in quality control to assess the conformity of an adhesive assembly procedure.

We have shown (1) that this test could be used quantitatively. Actually the wedge-test is a double cantilever stressed at constant displacement instead of a constant force. The length, lo, of the fracture induced by the wedge is related to the fracture energy through equation

[math]

where E is Young modulus of the adherend

e is the adherend thickness

h is the wedge heighth

When an adhesive bonded joint is placed in an agressive environment its resistance to fracture decreases. If the wedge-test is placed in that environment its fracture will proceed until equation (1) satisfies the new Ws value. Thus the wedge-test provides a means of measuring the resistance of an adhesive joint in a given environment. In general it is not known whether the assembly has or has not reached its equilibrium value, comparative values may then be obtained if one fixes the time after which the measurement is made. We give examples of the resistance to fracture of epoxy joints in humid environments, solvants and atmospheric pollution. These are comparable to those obtained by conventional methods which are longer and require more involved equipment.