Effect of laser treatment on strength of moisture-degraded epoxy adhesive joints and microscopic observation of treated surface

We examined the effect of laser processing surface treatment on the mechanical strength of adhesion.In addition to laser processing, double cantilever beam (DCB) and lap joint (LJ) specimens were prepared using an epoxy adhesive on aluminum plates that underwent acid etching, sandblasting, and acetone wiping.The open face method was employed to accelerate moisture degradation, and the tensile-shear strength and energy release rate of the specimens were measured.Laser processing resulted in remarkably high values of the measured energy release rate, even when the adhesive deteriorated.To examine the reason for the high strength, we performed a detailed fracture surface analysis and electron microscopic observation of the adhesive interface.When the interface of the fractured surface was observed, the laser treated surface was densely formed with fine filamentous protrusions that held the adhesive well.These filaments exhibited high oxidation resistance and achieved strong adhesion even when the adhesive and adherend deteriorated because of moisture.The laser treated adherend surface exhibited two strong anchoring effects owing to a significant increase in the surface area and the microfilamentous structure on the surface.However, the type of surface treatment did not have a significant effect on the LJ adhesion strength.