Braid is most commonly manufactured and used as a freestanding fabric with a constant braid angle (the acute angle measured from the axis of the braid to the axis of the bias yarns) for a given diameter.
Braided-fiber architecture resembles a hybrid of filament-wound and woven material. Like filament winding, tubular braid features seamless fiber continuity from end to end of a part. Like woven materials, braided fibers are mechanically interlocked with one another, but because the fibers are also continuous, braid has a natural mechanism that evenly distributes load throughout the structure.
This efficient distribution of load also makes braided structures very impact resistant. Since all the fibers in the structure are involved in a loading event, braid absorbs a great deal of energy as it fails. This is why braid is used as fan blade containment in commercial aircraft and for energy-absorbing crash structures in Formula One racing cars.
Braided fibers are coiled into a helix just like wire in a spring. The difference, however, is the mechanical interlocking. As a structure is exposed to high fatigue cycles, cracks will propagate through the matrix of filament-wound or unidirectional prepreg laid-up structures. While micro-cracking will occur in a braided structure, the propagation is arrested at the intersections of the reinforcing yarns. This is why braid is the reinforcement choice for aircraft propellers and stator vanes in jet engines.
Braid also greatly improves interlaminar shear properties when nested together with other braids. While interlaminar adhesion is no different from other reinforcement products, the layers move together. As a result, it is very rare for cracks to form and propagate between layers of braided reinforcement. Since braids are woven on the bias, they provide very efficient reinforcement for parts that are subjected to torsional loads. Braid is therefore an ideal reinforcement for drive shafts and other torque transfer components, such as flanged hubs.
Braid can also easily and repeatedly expand open to fit over molding tools or cores, accommodating straight, uniform cross-section forms as well as non-linear, irregular cross-section components, much like a sock conforms easily to a foot. This ability to slip onto tools and cores with speed, ease, and a high degree of repeatability, makes braid the ideal solution for products with changing geometries like prosthetics and hockey sticks.
Virtually any fiber with a reasonable degree of flexibility and surface lubricity can be economically braided. Typical fibers include aramid, carbon, ceramics, and fiberglass, as well as various natural and synthetic fibers and thermoplastics. A hybrid braid can also be formed using different raw materials to tailor the ultimate properties and optimize the reinforcement costs. Hybrids can be made using different yarns to create aesthetically pleasing patterns within the fabric that complements braid's naturally attractive symmetry. Braid can also be made in a virtually infinite variety of diameters or widths, fiber angles and areal weights.
