The Effect of Surface Preparation and Exposure Environment on the Bond Failure Processes in Adhesively Bonded Sheet Molded Composite (SMC)

Abstract The durability of adhesively-bonded composites has been investigated using a wedge-type specimen. Polyester-resin, fiberglass sheet molded composite (SMC) was bonded with a commercial two-part poly-urethane adhesive. The SMC composite received one of four different surface preparations: no treatment, abrasion, priming, or abrasion and priming. The wedge test was used to study the durability of the samples which were exposed to air and to the vapor above water, concentrated ammonium hydroxide, or methanol at 60[ddot]C. The crack length was measured during the experiments. The crack growth rate as a function of surface treatment varied in the manner: untreated ≈ abraded > primed ≈ abraded and primed. The crack growth rate as a function of vapor changed in the manner: methanol > ammonium hydroxide > water ≈ air. The samples were removed at the conclusion of the test and the failure mode was determined visually, by scanning electron microscopy (SEM), and by X-ray photoelectron spectros-copy (XPS). Initial insertion of the wedge resulted in substrate failure (delamination of the composite). Exposure of untreated and abraded samples under stress to the test vapors promoted adhesive failure. Primed and abraded/primed samples under stress and exposed to methanol vapor debonded via cohesive processes.