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The objective of this research was to examine the bamboo fiber preforming procedures and the effects of preforming on the mechanical properties. The bamboo fibers were bent to an angular shape by using mold compression. Different moisture contents were applied to the bamboo fibers before bending. Next, tensile tests were conducted on the preformed bent fibers to investigate the strength degradation caused by fiber damage during the forming process. Additionally, the vacuum preforming method, limited to a pressure of 1 atm, was used for bamboo fiber bending preforming. Different fillet radii of the angled shapes were used in the experiments to investigate the impact of the angle curvature at the bending points on the strength of the bent bamboo fibers. Unidirectional bamboo fiber mats were manually woven using polyester fiber lines and preformed with a closed mold. The fabrication of the unidirectional bamboo fiber/epoxy resin composites was conducted by vacuum-assisted resin transfer molding (VARTM). In this study, valuable insights into the design of the bamboo fiber preforming and composite manufacturing processes are provided, and our results can be used to contribute to the progress and utilization of the bamboo fibers in composite materials.

Non-precious iron-based catalysts (Fe–NCs) require high active site density to meet the performance targets as cathode catalysts in proton exchange membrane fuel cells. Site density is generally limited to that achieved at a 1–3 wt%(Fe) loading due to the undesired formation of iron-containing nanoparticles at higher loadings. Here we show that by preforming a carbon–nitrogen matrix using a sacrificial metal (Zn) in the initial synthesis step and then exchanging iron into this preformed matrix we achieve 7 wt% iron coordinated solely as single-atom Fe–N 4 sites, as identified by 57 Fe cryogenic Mössbauer spectroscopy and X-ray absorption spectroscopy. Site density values measured by in situ nitrite stripping and ex situ CO chemisorption methods are 4.7 × 10 19 and 7.8 × 10 19 sites g −1 , with a turnover frequency of 5.4 electrons sites −1  s −1 at 0.80 V in a 0.5 M H 2 SO 4 electrolyte. The catalyst delivers an excellent proton exchange membrane fuel cell performance with current densities of 41.3 mA cm −2 at 0.90 V iR -free using H 2 –O 2 and 145 mA cm −2 at 0.80 V (199 mA cm −2 at 0.80 V iR -free ) using H 2 –air. Single-atom catalysts consisting of isolated iron sites on a nitrogen-doped carbon matrix (Fe–N–C) are very promising cathode catalysts for proton exchange membrane fuel cells (PEMFC), but it is challenging to achieve a high density of single iron sites. Now, a synthetic approach is introduced to afford high-density Fe–N–C catalysts with a high PEMFC performance.

Hot press preforming of unidirectional prepreg composites plays a key role in the manufacturing of aerospace components. However, defect prevention remains challenging due to complex fiber reorientation and inter-ply friction phenomena that occur during the forming process. To address these challenges, this study proposes an integrated modeling approach comprising three key components: (1) a simplified linear friction model for characterization of inter-ply slip behavior, (2) a fiber-tracking algorithm that accounts for anisotropic deformation characteristics, and (3) a coupled linear shell–membrane formulation for simultaneous modeling of in-plane and out-of-plane deformation behaviors. The proposed approach is validated through comprehensive material characterization, finite element simulation, and experimental comparisons based on a 2 m Ω-stringer geometry. Simulation results align well with experiments, showing the model’s ability to predict defects. Parametric analysis also identifies temperature as a key factor in controlling interfacial friction and improving formability, with optimal results at 75 °C. This integrated modeling approach provides an effective approach for defect prediction and process optimization, contributing to reduced material waste and improved efficiency in aerospace composite manufacturing.

An application of a temperature control strategy based on a trust fuzzy clustering method (TFCM) and improved Wang-Mendel (WM) fuzzy rules extraction for a hot diaphragm preforming equipment is experimentally studied. This approach significantly improves both the accuracy of thermoset composite temperature control and the dynamic responsiveness of the thermal regulation system. The TFCM is adopted to extract the sample trust degree from the actual running data of equipment. And then on this basis, the improved method is adopted to extract fuzzy control rules from data which is developed in previous works. The temperature control of the equipment is realized by using the constructed fuzzy controller. The controller is composed of two input variables and one output variable. The temperature deviation and l temperature deviation rate of the composite material are the input variables, and the infrared (IR) lamp power is the output variable. To validate the proposed solution, experiments were conducted in practical engineering application scenarios. The method enables precise thermal gradient management with 94.5% fewer overshoot incidents compared to PID-based systems. The results show that the method has good robustness and high accuracy.

Wrinkles are urgent problems to be solved in the process of hot diaphragm preforming. Inter-ply slipping resistance is one of the causes of wrinkles. In this paper, based on the vertical inter-ply slipping test system, the inter-ply slipping behaviors of carbon fiber-reinforced epoxy resin composite prepregs were characterized. The mechanism of wrinkles caused by inter-ply slipping resistance was analyzed. According to the different characteristics expressed by the fiber and resin during the slip process, the inter-ply slipping behaviors of the prepregs were divided into three stages. The effect of temperature on the inter-ply slipping stresses was shown. The temperature will affect the viscosity of the prepregs. When the viscosity of the prepregs is low, the inter-ply slipping resistance will decrease. Based on the Coulomb friction law and the hydrodynamic equation, the inter-ply slipping kinetic equation of the prepregs was established. The inter-ply slipping kinetic equation was introduced into the ABAQUS main program by the ‘vfriction’ subroutine. The introduction of inter-ply slipping dynamics improved the accuracy of predicting the shape and position of wrinkles.

In this work, a novel five-step cold extrusion forging technology was proposed for fabricating a shaped charge liner with hyperboloid structure feature, in which three steps forming to develop the macroscopic hyperboloid shape and two steps annealing treatments to improve the microstructure and property of the liner. Besides, the preforming process was the focus of this investigation because the size structure, microstructure, and texture of the preform play a crucial role in the manufacture of the final forming process due to the heredity of dimension and microstructure, which also provides powerful process reference with the following forming steps. Based on the ABAQUS finite element (FE) platform, the cold extrusion process of the shaped charge liner preform was simulated, and the influences of forming parameters such as the initial billet size and friction coefficient between billet and dies on forming load, cavity filling, and strain distribution of the preform were investigated, respectively. The simulation results show that the optimal parameters of initial billet diameter and friction coefficient between dies and billet in cold extrusion preforming of shaped charge liner are 50 mm and 0.1, respectively. Additionally, the strain distribution of the shaped charge liner in the cold forming process was analyzed in detail. Finally, the experiment of the cold extrusion of the shaped charge liner preform was carried out to verify the feasibility of the cold extrusion process and the correctness of the simulation results.

Binders, or tackifiers, have become widespread in the production of new composite materials by liquid composite molding (LCM) techniques due to their ability to stabilize preforms during laying-up and impregnation, as well as to improve fracture toughness of the obtained composites, which is very important in aviation, automotive, ship manufacturing, etc. Furthermore, they can be used in modern methods of automatic laying of dry fibers into preforms, which significantly reduces the labor cost of the manufacturing process. In this article, we review the existing research from the 1960s of the 20th century to the present days in the field of creation and properties of binders used to bond various layers of preforms in the manufacturing of composite materials by LCM methods to summarize and synthesize knowledge on these issues. Different binders based on epoxy, polyester, and a number of other resins compatible with the corresponding polymer matrices are considered in the article. The influence of binders on the preforming process, various properties of obtained preforms, including compaction, stability, and permeability, as well as the main characteristics of composite materials obtained by various LCM methods and the advantages and disadvantages of this technology have been also highlighted.

An enhanced process for shaping thermoset fiber-reinforced composites using Modified Double-Diaphragm Forming (mDDF) in Prepreg Compression Molding (PCM) is proposed to address limitations in conventional forming quality. To minimize surface defects, prepregs were pre-cut to reduce wrinkle formation and trimmed after preforming. Complex geometries were managed through draping analysis, which enabled identification and mitigation of wrinkle-prone regions. A challenging layup configuration (±45/0/90/0/90/0/±45) was selected, and temperature-dependent behavior of the prepreg—such as resin fluidity and wrinkle characteristics—was evaluated from room temperature to 80 °C. Material characterization included tensile, bias extension, bending, friction, and density tests. Forming simulations using AniForm Suite 3.0 incorporated fitted material parameters for predictive analysis. Experimental validation confirmed that the mDDF process significantly improved fiber alignment and eliminated wrinkle defects, especially in 16 previously identified critical zones. The final parts exhibited superior surface quality and dimensional accuracy compared to conventional PCM, highlighting the potential of mDDF for precision manufacturing of complex thermoset composite structures.

A high percentage of folding defects were more easily introduced into the outer area of the sleeve hole during the mass production of track link forgings. In this study, it could be found that the folding defects were induced by the end-surface quality of the billet with the streamline characterization and the points tracking simulation. A defect elimination method based on the preforming design was proposed according to the numerical simulation and the experiment. The outer wall of the sleeve hole in the die cavity was shrunk inwards a certain distance to extrude the surface defects of the billet into the flash during the pre-forging. And then, the original flat shape punching wad of the sleeve hole was designed as an oblate-frustum of a cone shape to compensate the shortage of the material volume. The shrinkage range and the justified height of the oblate-frustum preform were recommended by the numerical simulation. As a result, the experiments showed that the proposed preforming design method completely eliminated the folding defects of the track link forgings.

The inter-ply sliding behavior is one of the important factors affecting the quality of carbon fiber composite products. In this paper, the inter-ply sliding behavior of the unidirectional prepreg was investigated for the preforming process. The inter-ply sliding resistance of prepreg under different conditions was measured by the homemade measuring device and the lubricating effect of inter-ply resin was identified by the micromorphology. The effect of fiber orientation was quantified by the combined roughness. With the increase of sliding distance, the inter-ply sliding resistance initially increased significantly, and finally maintained a constant value. A phenomenological model of the inter-ply sliding resistance was developed to explain the effects of pressure, velocity, and fiber orientation. This model can accurately describe the inter-ply sliding behavior of prepreg, which can be used for numerical simulation and the optimization of preforming process.