Fethi Abbassi

Additive manufacturing enables the fabrication of architected materials with geometries unattainable through conventional processes. Among these, auxetic metastructures, characterized by a negative Poisson's ratio, have attracted considerable interest owing to their unusual deformation mechanisms and superior energy absorption and dissipation. This study investigates the mechanical behavior of a tetrachiral tubular structure made of AA7075-T651 aluminum alloy under axial compression, focusing on the influence of boundary conditions at the part–machine interfaces. Finite element simulations accounted for frictional contact, geometric nonlinearity, and the rotational kinematics of tetrachiral cells. The results reveal that friction governs the onset and magnitude of the auxetic response. Under highly constrained contact (μ = 0.8), ligament rotation is suppressed, and the structure deforms conventionally, exhibiting a positive effective Poisson's ratio (ν ≈ +0.28), limited twisting (two turns), and a maximum compressive load of 3.877 kN. Reducing friction to μ = 0.2 with a fixed base promotes in-plane node rotation, activating the tetrachiral mechanism and yielding ν ≈ −0.25, four turns, and a higher load of 3.883 kN. The most pronounced auxetic response arises when both ends are free to slide under low friction, producing ν ≈ −0.32, five turns, and an 8.2% contraction of the outer diameter. Across the investigated configurations, the effective Poisson's ratio varies by 0.60. These findings demonstrate that the auxetic behavior of tetrachiral tubes is highly sensitive to frictional and kinematic constraints, which must be carefully controlled to ensure reproducible mechanical performance.

This study presents a novel approach to blend natural flax and chopped glass fibers. The fiber blends were in the form of mats with the composition as follows: 25% glass/75% natural fibers (G25/N75), G50/N50, and G75/N25. Mats of 100% natural fiber (N100) and glass fiber (G100) were prepared as benchmark samples. Fiber metal laminates (FMLs, 3/2)—based on hybrid fiber—were fabricated via autoclave method; metallic sheets from aluminium alloy 2024 were used. Quasi‐static mechanical tests including tensile and flexure tests were carried out whereas the Charpy impact test was conducted to represent the low‐velocity impact test. The results confirmed that chopped glass fibers enhance the mechanical performance of FMLs based on natural fibers. The tensile, flexural, and impact strengths of the 100% natural fiber FML (N100) were 109.9, 193.9 MPa, and 196.9 kJ/m ² , respectively. With the incorporation of glass fibers, the mechanical properties steadily improved across hybrid ratios G25/N75, G50/N50, and G75/N25; the maximum values of mechanical properties are recorded for G75/N25‐based FML including 198.5 MPa for tensile strength, 223.2 MPa for flexural strength, and 254.8 kJ/m ² for impact strength. Moreover, a finite element model of the 3‐point bending test for G50/N50‐based composite was developed. Both experimental and numerical models show the fracture in hybrid glass/natural fiber‐based FMLs was due to fiber breakage, matrix/fiber debonding, and plastic deformation extended to the fracture of metal layers. The study promotes manufacturing sustainable composites through the strategic blending of natural and glass fibers, reducing the environmental impact of glass fiber.

Interfacial strength at the metal‐adhesive joint is a pivotal parameter to define adhesive bond reliability and its overall mechanical performance. This study systematically investigates and optimizes sulfuric acid anodizing (SAA) parameters to promote the interfacial strength between aluminum Al2024 (Al) alloy and polyurethane (PU). Response surface methodology (RSM) was employed for the design of experiments by altering acid concentration, anodizing current, and time. Surface roughness and contact angle were measured to assess the effect of these parameters, while scanning electron and atomic force microscopies were employed to elucidate structure‐property relationships. SAA exceptionally enhanced the interfacial strength by increasing the contact area by creating a micro‐ and nano‐porous oxide layer, resulting in a 920% and 15 100% improvement in the single lap shear strength (SLSS) and fracture energy, respectively, after 45 min anodizing. By maximizing SLSS and minimizing cost through time, electric current, and concentration, RSM defined the optimum SAA conditions at 0.4144 M concentration, 1.0907A current, and 5.505 min; experimental measurements validated the optimized outcomes, showing respective increases of 600% and 6700% in SLSS and fracture energy. Also, the failure mode shifted from adhesive to predominantly cohesive mode. Additionally, different machine learning (ML) algorithms were trained using various combinations of anodizing and surface topography features; the most influential parameters were identified while mitigating overfitting despite the limited dataset. Among all tested ML models, support vector regression showed the highest accuracy, achieving a remarkable mean absolute percentage error of ≈11%. The study highlights the effectiveness of SAA to enhance Al/PU interface strength.