http://hdl.handle.net/10256/1544 2025-05-09T01:38:59Z http://hdl.handle.net/10256/26701 Cold Forming Hybrid Aluminium-Carbon Fibre-Reinforced Polymer Sheets Joined by Mechanical Interlocking Latorre Lázaro, Núria; Casellas, Daniel; Costa i Balanzat, Josep; Garcia-Llamas, Eduard; Pujante, Jaume Forming hybrid structures into complex shapes is key to address lightweighting of automotive parts. Recently, an innovative joining technique between aluminium and Carbon Fibre-Reinforced Polymer (CFRP) based on mechanical interlocking through sheet punching has been developed. However, scaling up the solution requires the assessment of challenges, such as multi-material forming and joint integrity, after forming operations. Therefore, this work proves the feasibility of forming aluminium-CFRP prepreg panels into complex omega-shaped profiles following a conventional cold-stamping process. Forming without defects was possible even in specimens featuring mechanical joints generated through punching. The effect of the CFRP position (in the inner or the outer side of the formed profile), the number of mechanical joints, the addition of a Glass Fibre-Reinforced Polymer (GFRP) intermediate layer to prevent galvanic corrosion and adequate lubrication on necking, cracking, springback behaviour and the final geometry after curing were studied. Compression tests were performed to assess the mechanical response of the hybrid profile, and the results showed that the addition of CFRP in the aluminium omega profile changed the buckling behaviour from global bending to axial folding, increasing the maximum compression load. Additionally, the presence of mechanical interlocking joints further improved the mechanical performance and led to a more controlled failure due to buckling localization in the geometric discontinuity 2025-04-24T00:00:00Z http://hdl.handle.net/10256/26572 Mechanosynthesis of Nanocrystalline Biphasic Ni-Fe Alloy Powders by Mechanical Alloying and Their Structural and Thermal Characterization Azabou, Myriam; Ben Mbarek, Wael; Wederni, Asma; Almenia, Sumaya; Khitouni, Mohamed; Suñol Martínez, Joan Josep An equiatomic Ni-Fe alloy was synthesized through mechanosynthesis, under an argon atmosphere using a planetary ball mill, after 100 h. To assess the phase stability, the alloy was subsequently annealed at 923.15 K for 2 h. At the end of mechanosynthesis, X-ray diffraction analysis revealed the formation of two distinct solid phases, FCC γ-NiFe (wt% = 90.3%) and BCC α-FeNi (wt% = 9.7%). The lattice parameter of the FCC phase stabilized at 3.5748 Å, whereas the BCC phase exhibited a lattice parameter of 2.6608 Å. The average crystallite size was determined to be around 7 nm with the lattice strains quantified as 0.48% for both phases. This significant refinement of microstructure indicates extensive plastic deformation within the grains. Scanning electron microscopy revealed an angular particle morphology with an average particle size of 8.15 µm. Differential scanning calorimetry (DSC) analysis identified an exothermic transition at 623.15 K, corresponding to the Curie temperature of nickel, and another one at 873.15 K, attributed to the Curie temperature of Ni3Fe. These results demonstrate the efficiency of mechanosynthesis in producing biphasic Ni-Fe nanomaterials with tailored properties, characterized by a dominant FCC phase with a highly deformed nanocrystalline structure. These findings highlight the great influence of mechanical milling on the structural properties of the Ni-Fe alloy in terms of a high density of stored crystalline defects 2025-02-28T00:00:00Z http://hdl.handle.net/10256/26379 Sedimentation patterns from turbidity currents associated to hydrodynamical transport modes Serra Putellas, Teresa; Soler i Ortega, Marianna; Colomer, Jordi Turbidity currents are mechanisms that transport sediment from continental landscapes into coastal areas and therefore into oceans, reservoirs and lakes. Turbulence at the head of the turbidity current maintains sediment particles in suspension provided the mixing is greater than the settling velocity of the particles being transported. However, both the depositional regimes of the particles in turbidity currents and the extent of the hydrodynamical regimes still need to be better related. Likewise, the associated sedimentary patterns need to be related to the type of particles that form a turbidity current. In this study, a set of lock-exchange experiments in a flume were conducted to determine the extent and development of a turbidity current composed of different granulometric sediments and sediment concentrations. Both the extent of the inertial regime and the onset of the self-similar regime were determined and found to be dependent on the d50 of the sediment and the Rouse number (i.e. the balance between particle sedimentation and mixing due to the gravity current development). The results obtained from the sedimentation patterns bring new knowledge in explaining the gradation of sediments in turbidites and its relationship to the longitudinal hydrodynamics of a turbidity current as it develops 2025-02-01T00:00:00Z http://hdl.handle.net/10256/25955 Analytical criterion to prevent thermal overshoot during dynamic curing of thick composite laminates Farjas Silva, Jordi; González Ruiz, Jose Antonio; Sánchez Rodríguez, Daniel; Blanco Villaverde, Norbert; Gascons i Tarrés, Marc; Costa i Balanzat, Josep Local overheating during curing of thermosetting resins is likely to occur for thick laminates or during fast curing. Overheating may lead to heterogeneous mechanical properties along the laminate thickness or even to an uncontrolled reaction. To avoid overheating, most thermoset resin manufacturers recommend a 'safe' cure cycle. However, these cure cycles can be improved to shorten cure times in thin laminates and may not be good enough to avoid overheating in thick laminates. In this paper, we propose a new analytical model to determine the critical thickness above which thermal runaway occurs when the laminate is heated at a constant rate up to a constant temperature. The model considers different thermal boundaries between the mould and the laminate, i.e., from a perfect thermal contact to a contact of infinite resistance. The analytical model was corroborated through the numerical integration of the equations governing it and experimental data from the curing process of a thick laminate composed of the commercial VTC401 epoxy resin and M55J carbon fiber system. Model predictions indicate that, under the manufacturer's recommended cure cycle, which includes an initial heating rate of 2 K/min, thermal runaway occurs in laminates thicker than 12.4 mm, aligning with experimental observations. A 20-mm-thick laminate, exceeding this threshold, was cured using a reduced heating rate of 0.3 K/min based on our criteria, successfully preventing overheating. The maximum temperature gradient recorded experimentally remained below 1 °C, confirming the model's prediction of uniform thermalization 2025-05-01T00:00:00Z