Effect of dry abrasion treatments on composite surface quality and bonded joints shear strength

Abstract

In order to enhance the adhesion properties of composites for further use in structural bonding applications, the effect of different surface treatments on flax/epoxy composite surface topography, surface arithmetic mean height (Sa), surface free energy ( γ s ) and composite to composite bonded joints shear strength (τ) was studied in this research. The main goal of this work was to evaluate the efficiency of abrasion surface treatments, such as sandblasting and sanding in enhancing composites’ adhesion quality compared to traditional mechanical surface treatments such as peel ply. Surface topography was evaluated using an optical microscope. Surface arithmetic mean height (Sa) was estimated via a mechanical surfscan. Surface free energy ( γ s ) was determined using the contact angle method along with the two-component Owens-Wendt model. Composite bonded joints shear strength was evaluated using the single lap shear joint test (SLJ). Trials revealed that specimens treated with sandblasting presented the highest composite bonded joints shear strength (τ). These specimens were characterized by a non-homogeneous surface topography, the highest surface arithmetic mean height (Sa) along with the highest surface free energy ( γ s ) and surface free energy dispersive component ( γ s d ).Unlike peel ply, sandblasting and sanding caused fiber exposure at the surface level. Sand granulometry used for sandblasting had an effect on the composite surface quality and its bonded joints shear strength. Linear regression revealed that composite bonded joints shear strength increases with the increase of the surface free energy dispersive component ( γ s d ). Abrasion treatments such as sandblasting significantly enhanced the adhesion properties of the composite compared to peel ply. Yet it did cause some side effects such as flax fiber damage and sand residue. These side effects could be reduced by opting for less harsh abrasive sand and more sophisticated cleaning processes.