Current Issue : July-September Volume : 2026 Issue Number : 3 Articles : 5 Articles
Sandwich structures are increasingly employed in high-performance applications due to their excellent strength-to-weight ratio. However, their mechanical reliability often depends on the structural core, which remains susceptible to failure under shear and flexural loads. Additive manufacturing (AM) enables the design and fabrication of complex, bio-inspired core architectures, such as those derived from Voronoi tessellations, which can potentially enhance energy absorption and mechanical performance. This study investigates the mechanical behavior of PLA-based cellular cores, produced via Fused Filament Fabrication (FFF), under quasi-static and intermediate strain rates (up to 33 s−1). Two infill geometries were compared: a standard cubic pattern and an open Voronoi-based structure inspired by biological morphologies. The results demonstrate strain-rate sensitivity in both configurations, characterized by increased stiffness and peak stress at higher loading rates. While the Voronoi structure exhibited lower maximum strength compared to the cubic pattern, it demonstrated a more gradual post-peak softening, indicating potentially superior energy dissipation capabilities. These findings support the potential of bio-inspired, additively manufactured structures in energy-absorbing applications....
Laser-directed energy deposition (DED) using wire or powder feedstock is a promising way to fabricate prototypes in rapid time, including complex metal parts for advanced engineering applications. In this work, AISI 316L stainless steel—a well-known, weldable alloy model—was used to perform a foundational comparative study of wire-fed (LWDED) and powder-fed (LP-DED) processes, establishing a baseline before progressing to high-temperature alloys. Hollow cylindrical specimens were fabricated and characterized microstructurally and mechanically. LP-DED produced a refined cellular–dendritic structure with primary dendrite arm spacing of 3.29 ± 0.49 μm and slightly higher average hardness (226 ± 8 HV0.2), accompanied by fine, spherical porosity inherent to the powder feedstock. LW-DED generated coarser epitaxial columnar dendrites (5.15 ± 0.69 μm) and slightly lower hardness (206 ± 10 HV0.2) but achieved nearly full density and high material catching efficiency. The results indicate that both methods yield comparable deposits when parameters are controlled, with LP-DED offering enhanced microstructural refinement and LW-DED providing faster deposition and higher build volume. These findings provide practical guidance for the additive manufacturing of high-performance parts and establish a baseline for the application of DED processes to advanced alloys....
Welded joints in API 5L X70 pipeline steel represent critical locations for pipelines intended for hydrogen service because welding can create microstructural inhomogeneity, stress concentrations, and uneven mechanical properties that can promote hydrogen-assisted degradation. In hydrogen-containing environments, these effects may manifest as reduced ductility, loss of fracture resistance, and increased cracking susceptibility, particularly in the weld metal and heat-affected zone. Therefore, welding procedures for X70 intended for hydrogen applications must be evaluated using systematic mechanical testing and microstructural characterization under defined hydrogen exposure conditions. The study investigates the detrimental effects of hydrogen on the mechanical integrity of pipeline materials, focusing on welded joints of the API 5L X70 steel, a candidate material for use in hydrogen-containing environments. The weldability and structural performance of the X70 pipeline steel joints in hydrogen environments, produced using automated multi-pass metal active gas (MAG) welding, was experimentally studied. Welding was performed on a DN800 pipe with precise control over welding parameters. Comprehensive analyses were conducted on the welded joints, including microstructure examinations, hardness measurements, slow strain rate testing in high-pressure gaseous H2 with a N2 baseline and fracture toughness testing. In high-pressure hydrogen SSRT showed a moderate reduction in ductility relative to nitrogen, with reduction of area decreasing from 81.2% (N2) to 69.1 and 71.5% (H2), while time-to-failure remained comparable (475 min in N2 vs. 497 and 496 min in H2) Ultimate tensile strength was not reduced (579 MPa in N2 vs. 609 and 597 MPa in H2). Secondary surface cracks were observed only on specimens tested in hydrogen. Fracture mechanics testing after hydrogen exposure yielded KIH values of 58–59 MPa √ min the weld metal and 57–61 MPa √ min the HAZ, exceeding the 55 MPa √ m acceptance threshold applied in this study. The results highlight the necessity of optimized welding techniques and targeted material analyses to ensure the safety and durability of pipelines in hydrogen-rich environments, thereby contributing to the development of reliable infrastructure for sustainable energy systems....
Pitch bearings are critical components in wind turbines, serving as the connection between blades and hub. Grease leakage and raceway edge damage are common failure modes of pitch bearings in engineering applications. Based on a practical engineering example, this paper presents a Finite Element Analysis (FEA) model of a pitch bearing system, in which contacts between steel ball rollers and raceways are simulated using nonlinear spring elements. This approach accounts for the flexibility of the entire pitch bearing system. Based on the FEA results, sealing capability of the sealing ring under system deformation is analyzed, revealing that the root cause of grease leakage in field applications is relative displacement between inner and outer rings, as well as breath effect. Additionally, contact loads and angles for each ball are derived from the FEA model and 3D solid local FEA models are constructed to investigate the impact of ellipse truncation on raceway load carrying capacity. The results highlight that ellipse truncation, caused by bearing deformation under flexible support structures, is a key factor in raceway edge damage....
This paper presents the results of a two-year innovative teaching project in the Vehicle Theory course, a fourth-year Mechanical Engineering subject at Universidad Carlos III de Madrid. The project explored the integration of generative artificial intelligence (GenAI) tools, particularly ChatGPT, to enhance student engagement, support project work, and promote ethical academic use. Key strategies included a flipped classroom approach, where students summarized previous lessons with GenAI assistance, and the use of AI to aid in the design and optimization of a tubular chassis project. Survey results and course observations indicate high student adoption of GenAI, with positive impacts on understanding theoretical concepts, completing exercises, and generating project outputs. Students reported that GenAI facilitated idea generation, technical problem-solving, and the creation of more effective and visually appealing presentations. Limitations included information bias, overreliance on GenAI, and variability in response quality depending on prompt formulation. Overall, the project improved attendance, engagement, and academic performance, highlighting the potential of GenAI as a complementary educational tool. Additionally, by requiring students to critically evaluate the GenAI responses, the project encouraged the development of judgment and decision-making skills, which are essential competences for future engineers....
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