Optically Stimulated Electron Emission Analysis of Surface Contamination Levels on Epoxy Composites and Effect on Failure Mode of Adhesively Bonded Specimens

摘要

Adhesive bonding is adversely affected by contamination on the adherend surfaces. Various surface monitoring techniques have been developed to assure that surfaces are sufficiently free from those contaminants, which can be adsorbed on to the adherend surfaces prior to applying the adhesive and degrade bond performance. Contaminants, even at low concentrations, can pose a risk to adhesive bonding and the durability of the bonded structure. It remains a challenge to measure residual surface concentrations of critical contaminant molecules (e.g. molecules from mold release agents) by current surface control procedures. Recently, we have made advances in an existing technique, optically stimulated electron emission (OSEE), originally developed for detection of contamination on metallic surfaces. Improvements in instrument design and in measurement analysis have extended this measurement modality to low levels of molecular species of contaminants on carbon fiber reinforced polymer (CFRP) materials. In this work, we present the basics of the measurement analysis and give some typical measurement results on smooth and laser ablated surfaces. We confirm the mercury spectral absorption mechanism of the contaminant species polydimethylsiloxane (PDMS), a major component of silicone-based mold release agents. Effects of PDMS levels on adhesive bond performance through analysis of double cantilever beam (DCB) testing is shown. Service life implications from failure modes of adhesive bonding onto PDMS-contaminated surfaces are made.