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Despite the advantages of thermoplastic resin, pultrusion process has struggled to create bidirectional laminates, resulting in weaknesses in joint connections and transverse properties. To tackle this issue, the study focuses on developing a methodology for pultruding bidirectional laminates. Initially, two types of sheet thermoplastic prepreg of glass fiber and polypropylene were produced: one with transverse (90°) orientation of fibers and another with longitudinal (0°) orientation of fibers. These sheets are then integrated into a single pack where fibers are oriented both transversely and longitudinally, and fed into the pultrusion machine. The resulting strip profiles (75 × 3.5 mm) demonstrate threefold increase in pin-bearing strength and transverse properties, showing a considerable promise for applications that demand robust joint connections and dimensional stability. The addition of transversely reinforced plies makes it possible for the pultruded profile to meet the EN 13706-3 requirements to mechanical performance. The bidirectional thermoplastic profiles produced in this study demonstrated high mechanical properties and are suitable for use in composite structures with bolted joints.

Considering the poor accessibility of the current finishing process for parts with complicated geometries, a novel bidirectional composite vibratory finishing (BCVF) approach was proposed, which combined the power actions on abrasive particles and processed workpieces. To examine the feasibility and effectiveness of the BCVF approach, comparative simulations based on discrete element method (DEM) and experimental validation were performed on a cylindrical workpiece simplified by a gear. Moreover, the effects of container size (or wall effects), media amount, workpiece position, and vibration parameters (including vibration amplitude and frequency) on the media-component interaction were systematically studied by DEM. The results show that the BCVF had the highest polishing efficiency, resulting in a workpiece surface roughness reduction rate up to 57% within 15 min. The distance between the container wall and the workpiece surface along the container width direction can be reduced to 4 d ( d is the abrasive particle diameter) with little effect on the finishing effect. Meanwhile, with the enhancing one-dimensional horizontal vibration, particle impact and shear effects are subsequently strengthened. In contrast, the media amount above the workpiece and the vibration along the workpiece axial direction are mainly effective for the shear effect. This BCVF approach provides reference for the finishing of various complex-shaped components including gears.

The bidirectional composite vibratory finishing (BCVF), which is a novel high efficiency collaborative surface finishing technology of structure shape and surface integrity, is expected to solve the problem of poor machinability in grooves, slits, corners, and intricate profiles of the workpiece. The basic research was carried out to expand its engineering applications. Based on the discrete element method (DEM), the particle flow behavior and velocity distribution were analyzed, it is found that the particle temperature can explain the changes of the normal and tangential cumulative contact energy on the workpiece surface. In addition, the normal contact force on the container sidewall and the pressure distribution on the workpiece surface were measured under different process parameters. The comparison with the simulations reveals that DEM model accurately predicted the particle–wall normal contact force frequency content, and the dominant frequencies are the container driving frequency and its multiplication. Meanwhile, the pressure-sensitive film can intuitively demonstrate the integrated action behavior of particles, including normal impact, inclined impact, rolling, scratching, and ploughing. Moreover, the axial uniformity and machining efficiency were enhanced by the rise in the frequencies and amplitudes of both horizontal and vertical vibration. For the combined effect of vibration frequency and amplitude, it was verified that the dimensionless vibration velocity amplitude was linearly and positively correlated with the normal contact force and the tangential cumulative contact energy on the workpiece surface. As a result, the simulations using spherical particles can predict some critical properties in non-spherical processing, and provide reference for the popularization of the BCVF process.

Alkali treatment on bamboo fibers were reported to improve the interface strength with epoxy resin as formed to a composite. In order to reduce the process time of alkali treatment, bamboo fibers were treated in alkali with different concentrations under the room temperature. The alkali treatment process for the bamboo fibers, which results in a higher tensile strength, was used for the subsequent studies. Unidirectional and bidirectional BF preforms were constructed in our laboratory. The unidirectional (UD) and bidirectional (BD) BF/EP composites were fabricated using the bamboo fibers treated with the selected BF alkali treatment process. Tensile properties were measured in both the longitudinal and transverse directions for the UD and BD BF/EP composites with different fiber volume fractions. The UD BF/EP composite has good reinforcement effect in the fiber direction and the tensile strength is compatible to the reported results. However, the transverse strength of UD composites is weaker than the pure epoxy. For BD BF/EP composites, tensile strengths in both the longitudinal and transverse directions all show some improvement as compared to the pure epoxy.

Replacing synthetic fibers with natural ones as reinforcement in polymeric composites is an alternative to contribute to sustainability. Pineapple leaf fibers (PALF) have specific mechanical properties that allow their use as reinforcement. Further, graphene oxide (GO) has aroused interest due to its distinctive properties that allow the improvement of fiber/matrix interfacial adhesion. Thus, this work aimed to evaluate the ballistic performance and energy absorption properties of PALF-reinforced composites, presenting different conditions (i.e., GO-functionalization, and variation of fibers volume fraction and arrangement) through residual velocity and Izod impact tests. ANOVA was used to verify the variability and reliability of the results. SEM was employed to visualize the failure mechanisms. The Izod impact results revealed a significant increase in the absorbed energy with the increment of fiber volume fraction for the unidirectional configuration. The ballistic results indicated that the bidirectional arrangement was responsible for better physical integrity after the projectile impact. Furthermore, bidirectional samples containing 30 vol.% of GO non-functionalized fibers in a GO-reinforced matrix showed the best results, indicating its possible application as a second layer in multilayered armor systems.

The aim of this in vitro study was to investigate the compressive strength and the bulk porosity of a bidirectional (bFRC) and an experimental bidirectional spiral winding reinforced fiber composite (bswFRC). Cylindrical-shape specimens were prepared for each material group and processed for the evaluation of compressive strength after different storage conditions (dry, 1 and 3 months) in distilled water at 37 °C. The specimens were also assessed for the degree of bulk porosity through X-ray tomography. A scanning electron microscope (SEM) was used to determine the fracture mode after a compressive strength test. Data were statistically analyzed using Two-Way Analysis of Variance (ANOVA). A significantly lower compressive strength was obtained in dry conditions, and after 1 month of water immersion, with the specimens created with bFRC compared to those made with bswFRC (p < 0.05). No significant difference (p > 0.05) was found between the two groups after 3 months of water immersion. However, the presence of water jeopardized significantly the compressive strength of bswFRC after water storage. The type of fracture was clearly different between the two groups; bswFRC showed a brutal fracture, whilst bFRC demonstrated a shear fracture. The bswFRC demonstrated higher pore volume density than bFRC. In conclusion, bswFRC is characterized by greater compressive strength compared to bFRC in dry conditions, but water-aging can significantly decrease the mechanical properties of such an innovative FRC. Therefore, both the novel bidirectional spiral winding reinforced fiber composites (bswFRC) and the bidirectional fiber reinforced composites (bFRC) might represent suitable materials for the production of post-and-core systems via CAD/CAM technology. These findings suggest that both FRC materials have the potential to strengthen the endodontically treated teeth.

In recent years, bidirectionally reinforced composite foundations have been widely used in highway, railway, and bridge engineering with notable results. The key mechanism is the soil-arching effect, which arises from the self-adjustment of the soil and directly affects the bearing capacity of the foundation. In this study, numerical simulation was employed to analyze the vertical stress in the subgrade soil and the transfer of particle contact forces from the macro and micro perspectives. The existence of the soil-arching effect was confirmed, and its variation under loading was revealed. To quantify the degree of the soil-arching effect, the stress transfer efficiency of the soil between piles was introduced. Subsequently, a bidimensional theoretical model was established based on the coordinated deformation among the embankment, the horizontally reinforced cushion, the vertical piles, and the soil. In this model, the combined effects of the embankment soil-arching, the reinforcement of cushion net, and the stress diffusion were incorporated. A method for the calculating of the pile–soil stress ratio of bidirectionally reinforced composite foundation was proposed, and the influence of various factors on this ratio was explored. The results indicate that the soil-arching effect can be divided into three stages according to the height of the subgrade fill: no-arch stage, transition stage, and soil-arching stage. Reducing pile spacing or increasing cushion thickness can improve the stress transfer efficiency. When the pile length is appropriate, the stress in the foundation soil at 0.55 times the pile depth was contoured, enhancing stability. The pile–soil stress ratio decreases with the increase in filling weight and pile spacing, increased first and then decreased with increasing internal friction angle of filling materials, and increased with the increasing height of embankment, the number of geogrid layers, and the cohesion of filling materials.

When creating polymer-based composites, plain weave fabrics and micron-sized fillers offer bidirectional strength and reduced voids/inhomogeneity. In the present work, It was investigated how glass fabric reinforced epoxy composite (G-E) performed during three-body abrasive wear with and without ceramic fillers (SiO2, Al2O3, graphite, and fly ash cenospheres). In experiments, loads of 20 N and 40 N were applied at various abrading distances of 500 m, 1000 m, 1500 m, and 2000 m. According to the results of sand abrasive wear test, the specific wear rates of G-E based composites are sensitive to fibre and filler/matrix adhesion. Under all tribo-test settings, the SWR for all particulate G-E composites decreases in the following order: G-E > Gr/G-E > SiO2/G-E > Al2O3/G-E > fly ash cenosphere/G-E. Furthermore, the specific wear rate of the fly ash cenosphere filled G-E composites were found to be lower than the G-E and other filler materials filled G-E composites. There was 38.7% reduction in the specific wear rate at 40 N, 2000 m in fly ash cenosphere filled G-E composite. As per the evidence of scanning electron microscope images of worn-out surfaces, mechanisms such as ploughing, fibre breakage, fibre pull-out, fibre thinning, and a network of microcracks caused the wear in composites.

At present, materials obtained from nature are adopted with high priority due to exploitation of natural resources ofthe materials. This work is focused on the use of natural fibre with nano-silica as reinforcement in epoxy resin as a matrix. The polymer composites were developed by mixing an appropriate amount of nano SiO 2 with bamboo fibres. After composite fabrication, specimens of standard size were prepared, and tests related to mechanical properties were performed. 32H compositesperformed best in the tensile test. The flexural test value for 32G composite was the highest. We found that the 32H composite had better energy absorption capacity. Response surface methodology (RSM) was used to find the optimum composition of composites, and the effects of fibre and nano-SiO 2 on their mechanical properties were investigated. A central composite design was employed to analyse the composite properties. A second order polynomial model was used for predicting strength of the composites. It has been found that the composite was best fit by a quadratic regression model with an excessive co-efficient to determine the R 2 value. Effects of bamboo fibre and nano-SiO 2 were examined using analysis of variance (ANOVA).Experiment found that two-layer natural bamboo fibre with 2 wt.% of silica is of high quality. Nano composites of fabricated natural fibre reinforced polymer has numerous uses in automotive, aircraft, aerospace, sporting, structural, and home appliance industries.

To overcome the poor mechanical properties of biomass aerogels in oil/water separations, three different freeze-casting methods were used including direct freezing, unidirectional freezing, and bidirectional freezing with sodium alginate (SA) aerogels reinforced with cellulose nanofibrils (CN). After chemical crosslinking and silane modification, compression testing revealed that the SA/CN aerogels with parallel lamellar microstructures prepared by bidirectional freezing exhibited super-elasticity with the minimal energy dissipation of ~ 0.04 in each cycle, a maximum compressive stress of 80.4 kPa, and minimal plastic deformation at ~ 4.15%. Additionally, the water and oil contact angle of the surface of the lamellar SA/CN aerogel was 148.7° and 0°, respectively. By combining the super-elasticity and hydrophobicity/superoleophilicity, the lamella SA/CN aerogels could be reused for the separation of oil/water mixture with oil absorption capacities up to 34 times its weight. Furthermore, the lamellar SA/CN aerogel could continuously separate oil/water mixtures with the assistance of a pump. Therefore, the present study offers a simple and environmentally friendly method for fabrication of super-elastic and hydrophobic/superoleophilic biomass aerogels that are applied to continuous removal of oil from water. Graphical Abstract