The application of coherent optics to the study of adhesive joints II. Holographic interferometry

The technique of holographic interferometry is complementary to the technique of speckle photography described previously. It allows the out‐of‐plane motion to be visualized with a sensitivity of about 0.3 μm. This technique has been applied to the study of the behavior of model glass‐glass joints bonded by different adhesives under shear stress. Its high sensitivity allowed the presence of stress concentrations at the ends of the joints to be shown in the case of high‐modulus adhesives and the existence of additional torsion and/or cleavage stresses to be demonstrated in the case of lower modulus adhesives. Work in progress should lead to more quantitative data.