CFRTP single-lap adhesive bonding and its mechanical performance enhanced by laser surface treatment: Finite element simulation and experimental validation

The outstanding mechanical properties of carbon fiber reinforced thermoplastic polymer (CFRTP) have led to its widespread application in many industrial sectors. In response to the engineering challenge of repairing large non-critical CFRTP structural components in situ, an infrared fiber laser surface cleaning technology is proposed to treat the bonding interface and enhance the tensile strength of polypropylene (PP)-based CFRTP single-lap bonded joints. Specifically, through single-factor and orthogonal experiments, the impact of different process parameters on the properties of the bonded joints was identified first. Then, online temperature monitoring was performed to elucidate the laser treatment mechanism of the CFRTP sample interface. Surface morphology of the laser-treated samples further indicates that when the temperature of the sample surface surpasses the resin decomposition temperature with extended holding time, the resin could be removed from the surface more thoroughly. Additionally, a novel three-dimensional woven finite element (FE) model, accounting for anisotropic heat transfer, was established to predict the surface temperature and cleaning quality of CFRTP. The FE model incorporates the anisotropic heat transfer characteristics of carbon fibers, thus accurately simulating the heat transfer behaviors between carbon fibers and the resin matrix. The laser ablation mechanism is elucidated by examining the surface ablation morphologies and peak surface temperatures. A comparison between experimental results and FE simulations demonstrated a notable coherence in the trend of surface morphology variations, with discrepancies in peak surface temperatures ranging from 3.29 % to 24.63 %. The experimental tests proved that the shear strength of single-lap bonded joints reaches its maximum value when the laser power is 35 W, the scanning speed is 2500 mm/s, and the number of scans is four. The enhancement of the mechanical properties of bonded joints can be attributed to the improved wettability and higher surface free energy of the laser-treated samples.