Abstract
Adhesive bonding of carbon-fiber-reinforced polymers (CFRPs) is a key enabling technology for the assembly of lightweight structures. Surface pretreatment is necessary to remove contaminants related to material manufacturing and ensure bond reliability. The present experimental study focuses on the effect of mechanical abrasion on the damage mechanisms and fracture toughness of CFRP/epoxy joints. The analyzed CFRP plates were provided with a thin layer of surface epoxy matrix and featured enhanced sensitivity to surface preparation. Various degrees of morphological modification and fairly controllable carbon fiber exposure were obtained using sanding with emery paper and grit-blasting with glass particles. In the sanding process, different grit sizes of SiC paper were used, while the grit blasting treatment was carried by varying the sample-to-gun distance and the number of passes. Detailed surveys of surface topography and wettability were carried out using various methods, including scanning electron microscopy (SEM), contact profilometry, and wettability measurements. Mechanical tests were performed using double cantilever beam (DCB) adhesive joints. Two surface conditions were selected for the experiments: sanded interfaces mostly made of a polymer matrix and grit-blasted interfaces featuring a significant degree of exposed carbon fibers. Despite the different topographies, the selected surfaces displayed similar wettability. Besides, the adhesive joints with sanded interfaces had a smooth fracture response (steady-state crack growth). In contrast, the exposed fibers at grit-blasted interfaces enabled large-scale bridging and a significant R-curve behavior. While it is often predicated that quality composite joints require surfaces with a high percentage of the polymer matrix, our mechanical tests show that the exposure of carbon fibers can facilitate a remarkable toughening effect. These results open up for additional interesting prospects for future works concerning toughening of composite joints in automotive and aerospace applications.
Highlights
Lightweight materials have played a significant role in product design since the inception of the aerospace industry
By reducing D, more matrix was removed from the carbon-fiber-reinforced polymers (CFRPs) surface with a consequent increase of exposed carbon fibers
We have investigated the effects of mechanical treatments, such as sanding and gritblasting, on the toughness of CFRP/epoxy joints
Summary
Lightweight materials have played a significant role in product design since the inception of the aerospace industry. Thermoset CFRPs have excellent properties, such as high strength, low weight, and corrosion and fatigue resistance, but the automotive industry application is limited due to the long production cycle [3]. For this reason, cured CFRP components are usually joined to the car body using a fastening method, such as riveting or bolting. The current pace of adoption in high-end products and critical load-bearing applications is still limited by the ability to join CFRPs efficiently [5]. Joining with structural adhesives emerged as a key-enabler of structural light-weighting because it allows for reduction of stress concentration and assembly cost and time, which are critical to the affordability of lightweight multimaterial structures [6,7,8,9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
