The physicochemical characteristics of carbon fiber reinforced polymer (CFRP) surfaces are critical for structural bonding. Achieving optimal adhesion remains challenging, as conventional treatments often involve aggressive chemicals or toxic residues. Plasma treatments offer an environmentally friendly alternative, inducing surface modifications such as increased roughness, enhanced hydrophilicity, incorporation of high-energy functional groups, and reactive sites formation. This study investigates argon, nitrogen, and oxygen plasma treatments on unidirectional carbon fiber/epoxy composites (CYCOM 5320-1) at varying power (20 and 50 W) and durations (600, 1200, 1800 s) to evaluate effects on surface activation, hydrophobic recovery, temporal stability, and bulk viscoelastic properties. Results show plasma effectively cleans and decontaminates surfaces while improving roughness and wettability. Argon plasma at low power and short duration increased roughness by ∼ 17% and enhanced existing functional groups. Nitrogen plasma at low power and longer durations increased roughness by 140% and introduced nitrogen-rich groups, improving wettability. Oxygen plasma produced the most substantial effects even at low power, with ∼200% roughness increase and incorporation of highly energetic oxygen-containing groups, favorable for structural adhesion. FTIR, XPS, SEM, and DMA analyses supported these findings, providing detailed insights into surface activation mechanisms.

The Plasma Electrolytic Oxidation (PEO) process was investigated to enhance the adhesion of AA2024-O aluminum alloy with a polyetherimide (PEI) matrix composite, using oxy-fuel welding (OFW). A Central Composite Design (CCD) statistical model was used to optimize three independent parameters in PEO: immersion time (s), duty cycle (%), and electrolyte concentration (Na₂B₄O₇·10H₂O), aiming to achieve a maximum value of shear strength of the hybrid joint (in MPa). The hybrid joint without PEO treatment presented a resistance of 2.2 MPa while the best condition presented a resistance of 9.5 MPa, resulting in a value 4× higher than the untreated material, due to the characteristics of the coating, which presented a more hydrophilic surface, allowing better mechanical interlocking with the polymer matrix and resulting in mixed-mode failure (adhesive, cohesive, and light fiber). In addition to improving adhesion, the PEO treatment provided better corrosion resistance to the alloy, forming an inert aluminum oxide (Al₂O₃) coating, with an improvement of approximately 99.84% compared to the untreated alloy. The statistical design covers about 77.15% of the total variability of the PEO + welding process, with independent factors influencing around 48.4% of the variability.

In this study, the AA1100 aluminum alloy underwent the plasma electrolytic oxidation (PEO) process to enhance its adhesion to a thermoplastic composite of polyetherimide (PEI) reinforced with glass fiber, following ASTM D1002:10 standards. A 2³ factorial design was employed, varying three parameters in the oxidation process: immersion time, applied electric potential, and electrolyte concentration (Na₂B₄O₇). The joining of aluminum and thermoplastic composite samples was achieved through oxy-fuel welding (OFW), using oxygen and acetylene gases. For the characterization of the joined samples, a universal tensile testing machine was utilized with a displacement speed of 1.5 mm/min. The analysis of the oxide coating involved scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FT-IR). Through variance analysis, it was determined that the statistical model encompasses approximately 80% of the variability in the adhesion process between materials. An improvement of up to 104% in adhesion between the materials was observed with the process, indicating an effective bond due to the presence of the thermoplastic matrix in the treated aluminum sample. This improvement is attributed to the morphology of the oxide coating, resembling corals, with micro-pores and recesses that facilitated mechanical anchoring.

This work aims to characterize the influence of hygrothermal conditioning on the mechanical and thermal behavior as well as the fractographic aspects of the interface of poly(ether imide) and glass fiber composite joints welded by electrical resistance using 400 mesh of AISI 304 stainless steel. The composites were mechanically characterized by Lap Shear Strength (LSS) and End Notched Flexure (ENF) testing to investigate maximum shear stress and energy from mode II interlaminar fracture toughness. Fractography was performed by SEM, while the influence on glass transition temperature and working temperature were evaluated by Dynamic-Mechanical Analysis and thermogravimetry. In the conditioned samples, the mechanical properties reduced 23% in the LSS test and 28% in the ENF test, while the fractography studies revealed elements of interlaminar and intralaminar fracture in both conditions. Thermal properties did not change significantly to disqualify this composite when applied to welding.

Resistance welding of thermoplastic composites critically depends on the quality of the metal–polymer interface formed between the heating element and the polymer matrix. However, the intrinsic chemical incompatibility between metallic heating elements and high-performance thermoplastics often limits joint strength and fracture resistance. In this study, we investigate the use of plasma-engineered siloxane coatings to tailor the interfacial properties of AISI 304 stainless-steel heating elements and enhance the performance of resistance-welded glass fiber/poly­(ether imide) (GF/PEI) joints. Thin films based on hexamethyldisiloxane (HMDSO) were deposited by plasma-enhanced chemical vapor deposition (PECVD), followed by oxygen plasma post-treatment to promote surface functionalization via the formation of polar groups. The modified interfaces were characterized by contact angle measurements, FTIR, XPS, and atomic force microscopy, revealing a transition from hydrophobic to highly polar surfaces driven by the incorporation of oxygen-containing species. Mechanical performance was evaluated by single lap shear strength (LSS) testing combined with detailed fractographic analyses using optical microscopy and scanning electron microscopy. The plasma-engineered interfaces exhibited an increase of approximately 48% in lap shear strength compared to untreated joints, accompanied by a clear transition in fracture mode from interfacial failure to intralaminar and mesh wire rupture mechanisms. These results demonstrate that plasma-deposited siloxane coatings provide an effective strategy to bridge the chemical gap in metal–polymer interactions, offering a versatile route for the design of high-performance welded interfaces in structural composite applications.

This study investigates the mechanical behavior of water-washable photosensitive resins used in masked stereolithography (mSLA) 3D printing, evaluating the effect of post-curing time (0, 5, 10, 30, and 60 min) and printing orientation (Flat [XY], Vertical [Z], and On-edge [XZ]) on the material characteristics. Specimens were manufactured according to ISO 527-2 type 1B and ISO 178 standards for tensile and bending tests, respectively. A Matlab algorithm was developed to automate the processing of experimental data. This tool enabled the extraction of parameters to fit distinct mathematical models for the elastic (linear) and nonlinear (polynomial) regimes, allowing the material response to be characterized at different curing times and print orientations. These models were implemented in Ansys Workbench for comparison with experimental results. The results show that increasing the post-curing time from 0 to 60 min raises the elastic modulus from 964.5 to 1892.4 MPa in the Flat [XY] orientation and from 774 to 1661.2 MPa in the Vertical [Z] orientation for tensile testing. In bending testing, the Flat [XY] orientation presented the best mechanical properties, while the Vertical [Z] and On-edge [XZ] orientations showed similar behavior. The numerical simulations adequately reproduced the experimental results, validating the developed constitutive models. Finally, a stress–strain correlation model is presented that enables estimation for any post-curing time between 0 and 60 min. This study provides essential data for optimizing 3D printing processes and developing structural applications with photopolymer resins.