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In this paper, a method for designing a two-dimensional (2D) braiding machine to braid preforms with special-shaped cross-sections is proposed. By means of splicing the running tracks of a traditional flat braiding machine's carriers, the 2D braiding machine can produce various structures with special-shaped cross-sections such as thin-walled cross-shaped, H-shaped, U-shaped, and T-shaped cross-sections, greatly expanding the application of 2D braiding. This paper studies the collisions of carriers after track splicing, dividing the collision problem into two categories, and putting forward a method to analyze whether the carriers collide. The judging method can not only verify whether there are collisions between carriers but also guide designers to change the layout of horn gears to avoid collisions. The mapping relation between the common arrangements of the carriers and the number of slots of the horn gears is also summarized, providing a theoretical basis for a future customized 2D braiding machine according to the practical needs. [ABSTRACT FROM AUTHOR]

This work examines the flexural and impact behavior of self-reinforced poly(ethylene terephthalate) (srPET) composites, which were produced by film stacking from fabrics composed of braiding commingled yarns with high-tenacity PET (serving as the reinforcements) and copolymerized PET (mPET) (serving as the matrix). The influence of the hybrid yarns, fabric architectures, and processing conditions on the mechanical properties of srPETs were studied. [ABSTRACT FROM AUTHOR]

Three-dimensional viscoelastic properties of four-step three-dimensionally (3D) braided composites are studied in this paper. Based on the three-cell division scheme, a multi-scale model for 3D braided composites is proposed. A periodic boundary condition is applied to characterize the periodic structure of 3D braided composites and yarns. Given the viscoelastic parameters of resin matrix and the elastic constants of fibers, the viscoelastic properties of yarns are obtained by the finite element method and Prony Series fitting. The three-dimensional viscoelastic constitutive relationship of interior cells is derived based upon the viscoelastic properties of yarns and resin matrix. Moreover, the viscoelasticity of 3D braided composites is studied by creep experiment. The viscoelastic deformation obtained from the multi-scale method agrees well with the experimental results. The influence of the two independent micro-structural parameters, braiding angles, and fiber volume fractions, on the viscoelastic properties of 3D braided composites is investigated in detail. [ABSTRACT FROM AUTHOR]

Three dimensional braided composite materials exhibit better performance in terms of structural integrity, through-thickness strength and impact resistance, than laminated composites. Other advantages regarding production are the ability to produce composite structures with intricate geometries close to the near-net-shape, and also with continuous changes in its cross-section. These properties are a consequence of the internal geometry of the 3D braided composites, in which yarns are interlaced following specific patterns programmed on a braiding machine. In this article, the operation of a typical rotary braiding machine is emulated in order to automatically obtain the geometry of a braiding unit cell. Once the geometrical description is obtained, a finite element model has been developed in order to carry out virtual testing of 3D composite materials. An AS4/epoxy braided material system has been virtually tested and a theory-experimental correlation has been performed for the longitudinal modulus and yield strength compression, using a failure criterion based on constituents and interface failures. [ABSTRACT FROM AUTHOR]

Abstract: A new parameterized finite element model (FEM) is established for 3-Dimensional (3D) five-directional rectangular braided composites. The model precisely simulates the spatial configuration of the braiding yarns and the axial yarns with consideration of the cross-section deformation as well as the surface contact in the braiding process. Moreover, this model orients in the same reference frame as the composites and the relationships among the structural parameters, particularly the braiding angle and the interior braiding angle, are investigated. A prediction of the effective elastic properties and the meso-scale mechanical response of 3D five-directional braided composites have been presented to verify the validation of the FEM. The effects of the braiding parameters on the mechanical properties are investigated in detail in this study. The results indicate that it is convenient to predict all the elastic constants of 3D five-directional braided composites with different parameters simultaneously using the FEM. Moreover, the FEM can successfully predict the meso-scale mechanical response of 3D five-directional braided composites containing periodical structures. In the mean while, the geometric characteristics and the mechanical properties of 3D five-directional and 3D four-directional braided composites have been compared. [Copyright &y& Elsevier]

Fibers are the basic structure in yarns, and yarns are the basic structure for fabrics. Although the approach described can be applied easily and naturally to fibers, especially when dealing with composite-material fabrics, the applications presented are thought of primarily as yarn-based assemblies. Hence, when talking about the developed model, 'yarn' and 'fiber' can be thought of as interchangeable. In general, fabric models assume underlying yarns to be of zero thickness. Those who have looked at yarns as three-dimensional structures have limited themselves to simple geometric arrangements of the yarns or have used assumptions which are non-geometric in order to simplify the model. A basic model is proposed which treats a yarn as a true three-dimensional solid object. This approach is first applied to three yarns twisted together to form a rope-like bundle. Next, the technique is used to model a woven fabric; the Peirce geometry is analyzed, and then the model is extended to look at fabric shear. An approach for a three-yam braid is presented as the most recent work. [ABSTRACT FROM AUTHOR]