This work proposes a novel solution for manufacturing hybrid metal-composite joints, in which different pin shapes are evaluated for their capability to penetrate long carbon fiber epoxy composites successfully and for the mechanical behavior determined by each configuration. On the metal side, pins are manufactured by Laser Powder Bed Fusion (LPBF), downsizing the currently adopted solutions and, at the same time, developing new blocking features aimed at enhancing the mechanical properties of the joint. The different configurations were evaluated in two distinct experiments: the first to evaluate the induced defects in the composite substrate and the second to characterize the mechanical behavior of the joint. It emerges that smaller pins produce much less damage and misalignments in the composite structure with respect to the conventional pin solution, whereas the new “blocking features” configurations consistently increase maximum pullout load and energy with respect to the conventional pin solution, with the same level of fiber damage.

This work proposes a novel manufacturing solution to locally reinforce a Sheet Molding Compound (SMC) with continuous fiber prepreg in a single-step compression molding operation. An adapted SMC process allowing for the manufacturing of continuous carbon fiber-reinforced SMC was successfully implemented, and a layer of fabric was added to mitigate the waviness induced during processing. Plates with different stacking sequences were manufactured and used for mechanical characterization to understand the effect of hybridization over tensile and flexural properties. It emerges that hybridization led to a 137% increase in tensile strength and up to 147% rise in flexural modulus compared to the standard SMC baseline. Additionally, the hybridization process helped reduce the variability in elastic and strength properties.

Interleaving elastomeric films into polymeric composite materials is a promising technological solution to manufacture components with localized functionalities. To optimize processing time and reduce testing costs, there is an urgent need for modeling strategies to predict the effect of hybridization based on the fundamental properties of singular constituents. In this work, three different laminates with varying numbers and positions of elastomeric layers were manufactured and mechanically tested in flexural configuration. The digital image correlation (DIC) technique is employed to evaluate the displacements and the strain field on the surface of the sample. A numerical framework for the prediction of the mechanical response, including damage initiation and evolution, was developed and validated against experimental data. The numerical results showed significant agreement with the experiments, reporting a maximum mismatch of about 10% in strain distribution and about 2% in the ultimate load. Additionally, degradation trends in the load vs. deflection curves were always consistent. Analysis of the fractured surface and predicted failure modes further demonstrated the reliability of the method.

Carbon fiber reinforced polymers (CFRP) are widely recognized for their exceptional strength-to weight ratio, making them ideal for advanced applications requiring superior mechanical performance and low weight. However, their heterogeneous composition poses challenges in both processing and surface treatment, which are crucial to improve the strength of bonded joints involving CFRP adherends. Laser processing technology offers several advantages in the processing of CFRPs, such as the effective removal of contaminants (e.g. mold release compounds) which hamper adhesion to structural adhesives. In this work, a UV picosecond laser is used to perform surface preparation of CFRP compression molding laminates. The proposed treatment not only cleans the matrix of release agents but also enables selective matrix removal without damaging the carbon fibers. Pre- and post-treatment surface morphology and chemistry are analyzed using a stereomicroscope, a digital microscope, a scanning electron microscope, and X-ray spectroscopy. The results are an improvement in the ultimate tensile strength of CFRP/CFRP single lap joints by more than 300% compared to the baseline untreated material. Furthermore, the fracture mode for laser-treated samples changes from adhesive to cohesive/fiber tearing, since the adhesive penetrates between the bare fibers.