1.1. Introductory remarks
It is well understood and documented in the literature that three-dimensional (3D) braided preforms provide unique structural features and performance characteristics to composites. Among those are: full delamination suppression, improved damage tolerance, impact resistance, fatigue life, exceptional torsional resistance, excellent bolt bearing strength, superior skin-stiffener pull-off strength, etc. Complementing these structural performance advantages, the usage of 3D braided integral, seamless, complex near-net-shape or net-shape preforms eliminates a number of labor-intensive operations from the manufacturing cycle, such as cutting and stacking multiple thin (2D) prepreg or fabric plies, tape slitting, or prepregging. In addition, additional manufacturing steps such as through-thickness stitching, z-pinning, etc., become unnecessary. All of the previous should allow for substantial preform cost reductions. After all, combining fully integrated 3D braided preforms with advanced resin infusion techniques such as resin transfer molding (RTM), vacuum-assisted RTM (VARTM), or pultrusion, should make it possible to radically simplify the composites' manufacturing cycle and significantly increase the cost effectiveness. As emphasized by Andrew Head (1998) in regard of the future of 3D braids, “The possibilities are limited only by the imagination!”
After reading the previous, one may reasonably ask: (1) why 3D braids are still not produced in high industrial volumes and (2) why are they still viewed as kind of “curiosity items,” not the prime candidates, when different concurrent composites' designs are evaluated for specific structural applications? It is not easy to answer these questions without a proper understanding of the uniqueness of 3D braided fabrics (regarding their manufacturing methods, dimensions, shapes, fiber architectures, and resulting performance characteristics) within the entire scope of all known textile materials, because that uniqueness determines both the strengths and weaknesses of 3D braids. In this chapter, the author attempts to address some fundamental accomplishments and persisting problems of 3D braiding technology with the primary focus on 3D braiding processes, machines, as well as existing and potential fabric products. Several decades of academic and industrial experience in the field of braiding in general, and 3D braiding in particular, help the author to take a broader look at both positive and negative aspects, and analyze them from different angles and perspectives. The ultimate hope is that this overview will help to understand the history and interconnections, assess the state of the art, and project future developments.
The chapter starts with establishing principal distinctions between 3D braiding on one side, and 2D braiding on the other, which results in a simple differentiation principle between respective braided structures. Then, a detailed overview of the historic origins and major developments in the field of 3D braiding processes and machines is presented. This first addresses what is known as “row-and-column 3D braiding,” mainly in retrospect, but emphasizing those accomplishments and persistent issues which are of a general value for any branch of 3D braiding technology. That category of 3D braiding methods has been flourishing from the late 1960s till the late 1990s, as is evident from the number of issued patents, conference publications, and journal articles, summarized in the book chapters cited in this chapter. During that period, the other principal direction, known under the names “3D rotary braiding” and “3D horngear braiding” (we prefer using the former name here), has been in relative obscurity with only a few valuable patents issued, such as Tsuzuki et al. (1991) as probably the most prominent example. That may look surprising because this direction of 3D braiding has a much longer history and also deep roots in the traditional Maypole-braiding and lace-braiding technologies. Those roots and interconnections are analyzed in detail further in the chapter. In fact, 3D rotary braiding has emerged again only in the early 2000s.
The second part of the chapter is focused on recent 3D rotary braiding developments, which have resulted in a breakthrough of 3D braiding technology and applications. A novel 3D rotary braiding method, machine concept, and control principle have been introduced in 2002 and patented in Mungalov and Bogdanovich (2002). Then, 3TEX, Inc., designed and built two automated 3D braiding machines, in which a bedplate was allowed to be fully populated by fiber carriers. The first machine had 16 horngears and 64 carriers plus 16 axials, and the other had 144 horngears with 576 carriers plus 144 axials. Those two machines opened new horizons for the future 3D braiding technology in several aspects. The first machine demonstrated a reliable ...