Study on Preparation of Triangular Melt-Spinning Poly (Vinyl Alcohol) Fibers and Its Fabric Strengthening and Toughening Epoxy

Fiber-reinforced epoxy materials have the advantages of light weight, high strength and designability, which are widely used in high-technology fields. In this paper, triangular poly (vinyl alcohol) (PVA) fibers prepared by melt spinning were used for the first time in reinforcing and toughening epoxy resins. Based on intermolecular complexation and plasticization, the triangular PVA fibers were successfully prepared via melt spinning and hot drawing. The thermal properties, crystallinity, morphology and mechanical properties of the triangular fibers with different draw ratios were characterized by DSC, FTIR, XRD, SEM and tensile testing. The results show that the comprehensive performance of the triangular fibers increased with the increase in the draw ratio. The tensile strength of triangular fibers increased from 0.3 to 4.22 cN/dtex. Then, the triangular PVA fiber and circular PVA fiber-reinforced and toughened epoxy materials were prepared, respectively. The mechanical properties of triangular PVA fiber/epoxy composites were higher than that of circular fiber-reinforced and toughened epoxy materials. Furthermore, the single-fiber pull-out test was used to analyze the interface capability of fibers and epoxy. The pull-out force of the circular fiber was 1.24 N, while that of the triangular fiber was 2.64 N. The specific surface area of the triangular PVA fiber was larger than that of the circular PVA fiber, which better made its contact with epoxy and was not easily pulled out. Experiments prove that triangular PVA fiber is an ideal material for strengthening and toughening epoxy resin.

Influence of Fiber Shape and Volume Content on the Performance of Reactive Powder Concrete (RPC)

This research studied the influence of three types of open (short-straight, long-straight, semicircular) and three different shapes of closed steel fibers (triangular, rectangular, circular) with different fiber contents by volume (0, 0.5%, 1%, 1.5%, and 2%) on the working and mechanical performance of reactive powder concrete (RPC). The results indicated that (1) the number of steel fibers and the enclosed area formed by closed steel fibers would remarkably impact the performance of RPC; (2) the semicircular fiber improves RPC’s strength the most among the three open shapes; (3) the short-straight fiber works more effectively than the closed steel fibers; (4) the circular fiber works the most efficiently in improving RPC’s mechanical performance while the triangular ones have the least effect among the three closed steel fibers; (5) both the closed and open steel fibers improve their compressive strength more than their flexural strength; (6) the closed steel fiber works more efficiently in improving the flexural strength but less efficiently in improving the compressive strength; (7) the open steel fibers enhance the mechanical performance of RPC via their anchoring performance while the closed steel fibers work by confining the concrete; (8) the hybrid utilization of steel fibers improves RPC’s mechanical performance to a higher level via combing the advantages of open and closed steel fibers.

Overlap-Stiffened Panels for Optimized Buckling Performance Under Minimum Steering Radius Constraints

Recent research on variable stiffness laminates have shown both numerically and experimentally that further improvement on the buckling behaviour is possible by incorporating overlaps that result in variable thickness profiles, with the thickness non-linearly coupled with the local steering angle. We present the concept of overlap-stiffened panels, developing a design method that allows for incorporating higher-stiffness regions into individual plies of a variable-angle tow (VAT) laminate, taking advantage of the non-linear coupling between the tow steering angles and the local thickness. The proposed method naturally copes with minimum steering radius constraints of different manufacturing processes, and the present study considers two tow steering processes: automated fiber placement (AFP) and continuous tow shearing (CTS). The minimum radius constraint is satisfied by connecting two transition regions of thickness specified on each ply by means of circular fiber tow arcs, of which the radius of curvature always exceed the minimum manufacturing constraint. Each individual ply exploring the overlap-stiffened design is described using 5 design variables. Laminates made up of these overlap-stiffened plies are optimized for a maximum volume-normalized buckling performance under bi-axial compression, measured through FEM, by a genetic algorithm and benchmarked against a straight fiber panel optimized for the same load case. The conclusion can be drawn that both AFP and CTS overlap-stiffened VAT panels can at least achieve the double of the volume-normalized buckling performance of an optimized straight fiber panel, demonstrating the potential of the proposed design method.

Study on filtration performance of elliptical fiber with different arrangements

The fibrous media composed of elliptical fibers is widely used owing to the high filtration efficiency. However, there are few studies on the arrangement of non-circular fibers, although the single non-circular fiber has been clearly investigated. In this article, two-dimensional numerical geometries of fibrous media with different elliptical fiber arrangements, namely, random distribution structure, dense–sparse structure, and bimodal structure, are developed for studying filtration performance. The results show that the large aspect ratio and solid volume fraction represent low particle penetration. When the particle diameter ( Dp) is small, the quality factor of bimodal structure is higher than the dense–sparse structure, especially at Dp = 50 nm. For the large Dp, the opposite is true. Meanwhile, reducing fiber diameter ( Df) is more significant than increasing solid volume fraction in terms of improving penetration. As for dense–sparse structure, replacing the elliptical fibers in sparse layers with circular fibers can comprehensively improve the quality factor of fibrous media. However, if the replacement between elliptical fiber and circular fiber occurs in dense layer, it will result in high quality factor at Dp ⩽ 500 nm, while low quality factor at Dp > 500 nm.