Effect of Adhesive Type and Surface Preparation on the Debonding Behavior of Glass and Carbon Fiber Reinforced Epoxy Adhesive Joints

In this work, the debonding behavior under quasi-static Mode I fracture loading of adhesive joints made on two types of composite materials with the same epoxy matrix and unidirectional carbon or glass fiber reinforcement was analyzed. Standard DCB tests were used to quantify the influence of adhesive type and substrate surface preparation on interlaminar fracture toughness. For the fabrication of the joints under study, three commercial structural adhesives from different manufacturers were selected, two epoxy-based and one acrylic-based. Substrate surface preparation was carried out using three different procedures: manual abrasion, sanding with P220 Al2O3 sandpaper, grit blasting with Al2O3, and peel ply PA80 polyamide fabric. The experimental results revealed the same trend for both epoxy-based adhesives: sanding provided the best results, regardless of the substrate used. Surface preparation by grit blasting proved highly sensitive to the applied parameters, generally yielding poorer results than manual sanding. Surface preparation using PA80 peel ply fabric may be a viable option. However, its main drawback is that it must be incorporated during composite manufacturing. The results demonstrate that fracture performance is governed by the interaction between adhesive chemistry and surface morphology rather than by surface roughness alone.