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Two-dimensional braided composite materials consist of an impregnated and cured braided fiber structure. The braid angle, which describes the orientation of fibers on the mandrel, affects the material properties of the composite part. Furthermore, braid production is often inaccurate, requiring quality assurance measurements of the fiber orientation. In this study, a frequency domain machine vision algorithm was applied to tubular braided preforms to measure fiber alignment during production. Several approaches to compensate for the tubular mandrel shape were tested and the fiber distribution in both the spatial and frequency domains was compared. The developed machine vision system allowed braid angle measurements to be made in real-time and in-line during the braiding process. The integration of such a system eliminates the need to make manual quality assurance measurements of the braided fiber structure, it further automates the braiding process, and it decreases production error. [ABSTRACT FROM AUTHOR]

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]

Three-dimensional braided composites have a skin-core structure and can be divided into three kinds of regions: interior, surface, and corner, which have different mechanical properties. Based on the structure characteristics and stiffness average volume formula, a new approach for testing and predicting longitudinal tensile modulus of three-dimensional braided composites is proposed in this paper. This approach can not only provide a basis to establish test standard for three-dimensional braided composites but also predict the longitudinal tensile modulus of three-dimensional braided composites. It is verified by an application example. Additionally, the effects of the number of rows and columns of yarns in preforms on longitudinal tensile modulus of three-dimensional braided composites are discussed here. [ABSTRACT FROM PUBLISHER]

This article reports the bending fatigue behavior of a four-step 3-D rectangular braided composite at different stress levels. The S–N curve and the stress vs. deflection history were recorded to investigate the bending fatigue behaviors of the braided composite. Specifically, the area of the stress hysteresis loop in each loading cycle and the accumulated area of the whole loading cycles were calculated from the stress vs. deflection history curves. All the integral areas were compared at different stress levels for analyzing the energy absorption. Then, the energy absorptions during the bending fatigue were compared to analyze the energy dissipation mechanisms taking place during the fatigue process. The stiffness degradation was also calculated to show the fatigue damage. The damage morphologies of the 3-D braided composite specimens were photographed to compare the failure modes under different stress levels. [ABSTRACT FROM PUBLISHER]

Braided and filament wound CFRP were fabricated with varied fiber orientations. These composites exhibited not only similar trends in their experimental strength and stiffness properties but also good correlations with predictions made by CLT. [ABSTRACT FROM PUBLISHER]

Microstructure of four-step 3D braiding preform with 1 x 1 pattern and complex rectangular cross-sections is studied by means of the control volume method. The complex rectangular configuration refers to the geometrical shape jointed by two or more rectangles together. Following the formation rule of the braiding process, the paths of the carriers are traced, particularly in the joint region where two rectangles join together. According to the formation procedures, three unit cell models, both topological and geometrical, are developed corresponding to the microstructure of the interior, surface, and corner in the joint region. The study shows that, in the joint region, the control volume of the unit cell is a cube in the interior, a hepta-prism in the corner, and a penta-prism in the surface, respectively. In addition, the study is able to demonstrate the difference in the braiding pattern and the spatial orientation of braiding yarns in the unit cells between those in the joint region of a complex rectangle and the corresponding region of a simple rectangle by four-step braiding process. [ABSTRACT FROM AUTHOR]

This paper proposes a method of deriving the engineering and strength properties of unidirectional lamina from laminate properties. Simple straight-sided untabbed tension and compression specimens are used to obtain the laminate properties. The derivation approach is an extension of existing methods that use cross-ply or angle-ply test specimens and back-out factors (also known as cross-ply factors) to derive unidirectional lamina strengths in the fiber direction. This method may reduce the cost of testing and improve the accuracy of strength predictions. It may be used to characterize some newer material forms such as two-dimensional braids. [ABSTRACT FROM AUTHOR]