Surface morphology optimization of thermoplastic composites for structural bonding using Abrasive Waterjet texturing
Topic(s) : Industrial applications
Co-authors :
Pierre FREQUELIN (FRANCE), Rédouane ZITOUNE , Julien JUMEL (FRANCE), Agathe JAILLON (FRANCE)Abstract :
Surface modification of thermoplastic polymers is gaining attention with the increasing proportion of high-performance thermoplastic composites in the transportation industry. Although appreciated for their impact resistance, recyclability, and low manufacturing constraints, their weak adherence to most adhesive substances is slowing down their development. Without chemical affinity to form strong bonds, it is generally recommended to increase substrate roughness to favour mechanical anchoring of the adhesive [1]. Techniques such as grit blasting or sanding are often employed to prepare surfaces before adhesive application. However, they can be challenging to industrialize, notably because of harmful particles and waste management issues.
Abrasive Waterjet (AWJ) is a possible alternative for reliable surface functionalization, as the water flux accompanying the particles impedes heating of the material, cleans the surface, and contributes to reducing the number of embedded particles [2]. Some optimal surface morphology is to be found, as overpronounced asperities will not allow for a good penetration of the adhesive and lead to voids [3]. In fact, a parabolic relationship seems to exist between the crater volume generated on 3D woven CFRP by AWJ texturing and the critical energy release rate of CFRP/CFRP bonded assemblies [4].
As the abrasive particles in the jet reach the target-surface, they form micro-craters whose average geometry and number density will vary with the process parameters (i.e., pump pressure, particle size, jet travel velocity). After a characterization of the crater formation process on Poly-Ether-Ketone-Ketone for a wide range of jet parameters, we derive new parameters with physical meaning, such as average crater spacing, as well as predict the topological properties of textured surfaces. In order to study the influence of surface topology on the adhesive performance of carbon fibre reinforced thermoplastic samples with an epoxy adhesive, the single lap joint tensile strength associated with 24 relevant AWJ configurations has been assessed and then compared to 3 industrial reference states.
Key findings:
•AWJ texturing improved the strength of CFR-PEKK/FM300M bonds for a wide range of parameters and with good repeatability. Fracture surfaces showed predominantly cohesive failure inside the adhesive.
•Roughness indicators (Sa, Sq, Sz, etc.) of tested textured surfaces are correlated with process parameters in a consistent and physically expected manner. As of yet, no clear link could be made between morphology and bond strength, as the values are all very close to the strength of the adhesive.
Abrasive Waterjet (AWJ) is a possible alternative for reliable surface functionalization, as the water flux accompanying the particles impedes heating of the material, cleans the surface, and contributes to reducing the number of embedded particles [2]. Some optimal surface morphology is to be found, as overpronounced asperities will not allow for a good penetration of the adhesive and lead to voids [3]. In fact, a parabolic relationship seems to exist between the crater volume generated on 3D woven CFRP by AWJ texturing and the critical energy release rate of CFRP/CFRP bonded assemblies [4].
As the abrasive particles in the jet reach the target-surface, they form micro-craters whose average geometry and number density will vary with the process parameters (i.e., pump pressure, particle size, jet travel velocity). After a characterization of the crater formation process on Poly-Ether-Ketone-Ketone for a wide range of jet parameters, we derive new parameters with physical meaning, such as average crater spacing, as well as predict the topological properties of textured surfaces. In order to study the influence of surface topology on the adhesive performance of carbon fibre reinforced thermoplastic samples with an epoxy adhesive, the single lap joint tensile strength associated with 24 relevant AWJ configurations has been assessed and then compared to 3 industrial reference states.
Key findings:
•AWJ texturing improved the strength of CFR-PEKK/FM300M bonds for a wide range of parameters and with good repeatability. Fracture surfaces showed predominantly cohesive failure inside the adhesive.
•Roughness indicators (Sa, Sq, Sz, etc.) of tested textured surfaces are correlated with process parameters in a consistent and physically expected manner. As of yet, no clear link could be made between morphology and bond strength, as the values are all very close to the strength of the adhesive.