Laser treatment design for CFRP bonding: an innovative approach to reduce process time

Generally, the production of structural parts in fiber-reinforced polymer with complex shape or big dimensions can be difficult to achieve. Therefore, it could be preferable to produce simpler parts, which are often assembled through fastening systems or bonding with structural adhesives. In the latter case, polymer composites should be pretreated before bonding to obtain a reliable structure. For this, laser systems can represent a repeatable and very attractive solution for pretreating polymer composites. However, often the time required for realizing the pre-treatment could lead to the choice of other technologies by the manufacturer. In this article, an innovative approach to design the laser texturing for bonding CFRP is presented. Based on the assumption that only the interfaces subjected to higher stress values should be pretreated, it allows a reduction in process time. In fact, the developed method allows to design the pretreatment process as a function of the stress field on which the joint is subjected. Experimental results demonstrate a 63 % increase in shear strength for fully treated specimens compared to untreated controls, with optimized treatment yielding equivalent performance at a normalized treated area of 0.4. Numerical predictions showed strong agreement with experimental results, with a discrepancy of only 3 ÷ 4 %, validating the model's accuracy. Additionally, the treatment time was reduced by approximately 60 % without a significant loss in joint strength. This approach, transferable to complex joint geometries, enhances the efficiency and viability of laser pretreatment for CFRP bonding.