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 vario us 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 surfa ce using roughness and wettability measurements, and this investigatio n shows the influence of substrate roughness characteristics on wettab ility and on the mechanical properties of adhesive joints. The micro-g eometry of the substrate surface needs to be taken into account if one is interested in the influence of the roughness. We have tested adhes ive joints that were made using different sheets under high strain rat es. The surface of sheet was either untreated or modified by a chemica l or mechanical treatment. The results showed that the shear strength of the adhesive joint is maximal when the sheet possesses an optimum s urface 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.