THE EFFECT OF SUBSTRATE ROUGHNESS CHARACTERISTICS ON WETTABILITY AND ON THE MECHANICAL-PROPERTIES OF ADHESIVE JOINTS LOADED AT HIGH-STRAIN RATES

This study describes the influence of the surface characteristics of a substrate on the joint strength in the case of a metal/polymer/metal sandwich. The objective was to evaluate the impact resistance of various adhesively bonded joints subjected to shear loading. The first part is devoted to the evaluation of the shear strength of adhesive joints at high strain rates using the Hopkinson pressure bar technique. The macroscopic approach enables us to compare different adhesive joints. The second part deals with the characterization of the substrate surface using roughness and wettability measurements, and this investigation shows the influence of substrate roughness characteristics on wettability and on the mechanical properties of adhesive joints. The micro-geometry of the substrate surface needs to be taken into account if one is interested in the influence of the roughness. We have tested adhesive joints that were made using different sheets under high strain rates. The surface of sheet was either untreated or modified by a chemical or mechanical treatment. The results showed that the shear strength of the adhesive joint is maximal when the sheet possesses an optimum surface morphology. This is related to the average roughness R(a), the width of valleys, and the dominance of valleys or peaks. Contact angle measurements confirmed the effect of roughness.