Search Results (8)

To bridge the mechanical performance gap between polyethylene terephthalate (PET) foam cores and balsa wood in wind turbine blades, this study proposes a hierarchical groove-perforation design for structural optimization. A finite element model integrating PET foam and epoxy resin was developed and validated against experimental shear modulus data (α < 0.5%). Machine learning combined with a multi-island genetic algorithm (MIGA) optimized groove parameters (spacing: 7.5–30 mm, width: 0.9–2 mm, depth: 0–23.5 mm, perforation angle: 45–90°) under constant resin infusion. The optimal configuration (width: 1 mm, spacing: 15 mm, angle: 65°) increased the shear modulus by 9.2% (from 125 MPa to 137.1 MPa) and enhanced compressive/tensile modulus by 10.7% compared to conventional designs, without increasing core mass. Stress distribution analysis demonstrated that secondary grooves improved resin infiltration uniformity and interfacial stress transfer, reducing localized strain concentration. Further integration of machine learning with MIGA for parameter optimization enabled the shear modulus to reach 150 MPa while minimizing weight gain, achieving a balance between structural performance and material efficiency. This hierarchical optimization strategy offers a cost-effective and lightweight alternative to balsa, promoting broader application of PET foam cores in wind energy and other high-performance composite structures. Full article

The handling and fluidization of amorphous soft solids, such as emulsions, foams, or gels, is crucial in many technological processes. This is generally achieved by applying mechanical stress that overcomes a critical threshold, known as yield stress, below which these systems behave as elastic solids. However, the interaction with the walls can facilitate the transition from solid to fluid by activating rearrangements of the fluid constituents close to the wall, resulting in increased fluidity of the system up to distances greater than the spatial scale of the rearrangements. We address the impact of wedge-shaped microroughness on activating the fluidization of emulsion droplets in pressure-driven flow through microfluidic channels. We realize the micro wedges by maskless photolithography to texture one wall of the channel and measure the velocity profiles for flow directed accordingly and against the increasing ramp of the wedge-shaped grooves. We report the enhancement of the emulsion flow in the direction of the climbing ramp of the wedge activated by increasing the magnitude of the pressure gradient. A gain for the volumetric flow rate is registered with respect to the opposite direction as being to $30\%$, depending on the pressure drop. Full article

This study created ceramic preforms with a 3D network structure (TAD_3D) by using treated aluminum dross (TAD) and kaolin slurry, with 30 ppi polyurethane foam as a template via the sacrificial template method. TAD_3D/5A05Al composites were then produced via pressureless infiltration of 5A05Al aluminum alloy into TAD_3D. The corrosion behavior and resistance of TAD_3D/5A05Al in salt spray were assessed via neutral salt spray corrosion (NSS), scanning electron microscopy (SEM), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) tests. The results showed that after 24 to 360 h of NSS corrosion, the corrosion of the 5A05 matrix was primarily pitting, with pits expanding and deepening over time, and showing a tendency to interconnect. The main corrosion products were MgAl₂O₄, Al(OH)₃, and Al₂O₃. As corrosion progressed, these products increased and filled cracks, pits, and grooves at the composite interface on the material’s surface. Corrosion products transferred to the grooves at the composite interface and grew on the ceramic surface. Corrosion products on the ceramic framework and the Al matrix can form a continuous passivation film covering the composite surface. PDP and EIS results indicated that the composite’s corrosion resistance decreased by 240 h but increased after that time. After 240 h, the surface passivation film can weaken corrosion effects and enhance the composite’s resistance, although it remained weaker than that of the uncorroded samples. Additionally, grooves at the composite interface deepened over time, with loosely structured corrosion products inside, potentially leading to severe localized corrosion. Full article

Designing effective thermal management systems within transmission systems requires simulations to consider the contributions from phenomena such as hydrodynamic lubrication regions. Computational fluid dynamics (CFD) remains computationally expensive for practical cases of hydrodynamic lubrication while the thermo elasto-hydrodynamic lubrication (TEHL) theory has demonstrated good accuracy at a lower computational cost. To account for the effects of hydrodynamic lubrication in high-power transmission systems requires integrating TEHL into a CFD framework such that these methodologies can be interfaced. This study takes an initial step by developing a TEHL solver within OpenFOAM such that the program is prepared to be interfaced with a CFD module in future versions. The OpenFOAM solver includes the Elrod–Adams cavitation model, thermal effects, and elastic deformation of the surfaces, and considers mixing between the recirculating flow and oil feed by applying energy and mass continuity. A sensitivity study of the film mesh is presented to show the solution variation with refinement along the circumferential, axial and radial directions. A validation case is presented of an experimental single axial groove journal bearing which shows good agreement in the pressure and temperature results. The peak pressure in the film is predicted within 12% and the peak temperature in the bush is predicted within 5% when comparing the centerline profiles. Full article

This study optimized and proposed a Warren truss slot-hole structure with a double-sided, square shallow slot and vertical and horizontal corrugated symmetry, achieved with inclined holes based on the stability and a good bearing capacity of an inclined strut truss structure. The tetrahedral truss lattice cells were obverse and reverse-staggered in the central core of the structure. Compared with the double-sided, square shallow groove cylindrical straight hole, the resin consumption of the Warren truss slot holes was similar to that of a vacuum-assisted resin infusion; however, the external flat compression force of the Warren truss slot holes on the resin stiffener structure doubled, and its bending contact force increased by approximately 1.5 times. Furthermore, the resulting Warren truss-slotted resin structure exhibited a late failure time. Compared with the double-sided, square shallow groove cylindrical straight hole foam-core sandwich composite, the Warren truss slot resin-stiffener-reinforced sandwich composite exhibited an increase of 4.7 kN in the flat compression load, an improvement of ~40% in flat compressive strength performance, an increase of ~0.58 kN in the bending load, and an improvement of ~60% in the bending strength, demonstrating its better bearing strength performance. Full article

Composite sandwich structures are widely used in the fields of aviation, marine, and energy due to their high specific stiffness and design flexibility. Improving the mechanical properties of the cores is significant to the strength, modulus, and stability of composite sandwich structures. Two kinds of core machining configurations were designed by combining thin grooves, perforated holes, and thick contour cuts as well as non-machining plain cores. The cores and sandwich structures with these configurations were fabricated using a vacuum-assistant infusion process. Static tensile, compressive, shear, and peeling tests were conducted on the infused cores and sandwich structures. The results showed that the tensile, compressive, and shear moduli, and compressive strength of the infused cores can be greatly improved. The tensile strength changed negligibly due to stress concentration induced by irregular foam cell and the shear-lag phenomenon of the resin column/foam interface. The shear strength of the infused cores increased slightly. The thick contour cuts and perforated holes can greatly improve the face sheet/core peel capacity of the sandwich structures, whereas the thin grooves can moderately improve the peel capacity. Both infused cores with the designed machining configurations exhibited positive effects on the compressive, tensile, and shear moduli, and compressive strength, considering the material costs. The study provides a comprehensive and quantitative insight into the effects of core machining configurations on mechanical properties of infused cores and composite sandwich structures. Full article

This study provides an overview regarding enhancement of an air-cooled heat sink applicable for electronic cooling subject to cross-flow forced convection. Some novel designs and associated problems in air-cooled heat sinks are discussed, including the drawback of adding surfaces, utilization of porous surfaces such as metal foam or carbon foam, problems and suitable applicable range of highly interrupted surfaces (louver or slit) and longitudinal vortex generator. Though the metal foam may accommodate significant surface area, it is comparatively ineffective for air-cooling application due to its much lower fin efficiency, and this shortcoming can be improved by integrating with solid fin. For highly dense fin spacing (e.g., <1.0 mm), cannelure or grooved surface may be a better choice, and fin structure with periodic contraction and expansion may not be suitable for it introduces additional pressure drop penalty. The partial bypass concept, which manipulates a larger temperature difference at the trailing part of heat sink, can be implemented to significantly reduce the pressure drop. Through some certain niche operation, t the thermal resistance of the partial bypass heat sink may be superior to the conventional heat sink. The trapezoid fin surface featuring easier manufacturing and a smaller weight is shown to have competitive performance against traditional rectangular fin geometry. The IPFM (Interleaved Parallelogram Fin Module) design which combines two different geometrical fins with the odd number fins being rectangular shape, and parallelogram shape in even fin numbers, shows 8%–12% less surface than conventional design but still offers a lower thermal resistance than the conventional rectangular heat sink in lower flowrate operation. The cross-cut design shows appreciable improvements as compared to the conventional plate fin design especially in high velocity regime and the single cross-cut heat sinks are superior to multiple cross-cut heat sinks. Full article

The resin flow behavior in the vacuum assisted resin infusion molding process (VARI) of foam sandwich composites was studied by both visualization flow experiments and computer simulation. Both experimental and simulation results show that: the distribution medium (DM) leads to a shorter molding filling time in grooved foam sandwich composites via the VARI process, and the mold filling time is linearly reduced with the increase of the ratio of DM/Preform. Patterns of the resin sources have a significant influence on the resin filling time. The filling time of center source is shorter than that of edge pattern. Point pattern results in longer filling time than of linear source. Short edge/center patterns need a longer time to fill the mould compared with Long edge/center sources. Full article