An Introduction To 3-D Weaving
Part one of a two-part series about 3-D weaving and its current and potential applications
In today's technical textiles marketplace, when people mention 3-D weaving or 3-D fabrics, they usually are referring to a growing category of products used primarily in highly performance-driven composite applications. Such applications range from jet engine components and engineered shapes to composite billets for bulkheads and ballistic armor panels. The attraction and interest in 3-D woven products specifically for composite applications stems from the following attributes:
- design flexibility and versatility;
- inherent resistance to delamination;
- improved damage tolerance;
- ability to tailor composite properties to the application;
- near net-shape preform capabilities; and
- reduced lay-up complexity and handling time.
This close-up cross section of a thick 3-D woven glass billet shows the layer-to-layer weave configuration.
Reviewing The Basics
Though composite applications are currently the primary use for 3-D woven products, there is vast potential for future applications, both within the composites marketplace and in non-composite applications as well. In an attempt to clarify and hopefully define what constitutes 3-D weaving or a 3-D woven fabric, a brief review of traditional weaving might be helpful.
According to Wikipedia.com, "weaving is a method of textile production in which two distinct sets of yarns or threads are interlaced at right angles to form a fabric or cloth." And, as many may recall from some weaving instructor in the past, the weaving process historically is defined by repeating a basic four-step cycle:
- Shed formation: An opening is created in the warp, or machine-direction, yarns for the weft, or filling, yarn to pass through. The subsequent shed changes create the weave's pattern.
- Weft, or filling, insertion: The weft yarn is inserted in the shed.
- Beat-up: The weft yarn is beaten into the fell of the cloth.
- Take-up and let-off: The resultant fabric is taken-up from the fell, and a corresponding amount of warp yarn is let-off to fill the void.
Successful repeats of this cycle result in the production of a woven fabric. Most people tend to think of and recognize conventional woven fabrics as roll goods having a clearly defined length and width, but very little discernable depth or thickness. In the composites marketplace, primarily because of their lack of discernable depth, these traditional woven fabrics, while possibly made from carbon, fiberglass, aramid, or any variety of combinations, are generally understood to be two-dimensional, or 2-D, fabrics. 3-D fabrics are the same in principle as 2-D fabrics, but possess a noticeable third dimension of significant depth or thickness created during the 3-D weaving process.
In an orthogonal, or through-thickness, weave, the weaving and connecting of lengthwise warp and crosswise fill layers generate inherent through-thickness physical properties in the fabric.
Adding A Third Dimension
The same basic four-step weave cycle applies to both 2-D weaving and 3-D weaving, but to create the third dimension, additional warp yarns are manipulated into multiple layers. This manipulation of the warp, with multiple layers woven in sync using extra filling insertions, creates the fabric's depth by weaving through the thickness — commonly referred to as through-thickness. The through-thickness weaving and connecting of warp and fill layers generates the 3-D woven fabric's highly desirable and inherent through-thickness physical properties.
Generally, 3-D fabrics are produced on customized or purpose-built weaving machines, which most likely incorporate a Jacquard unit to control the action of each warp yarn independently via computer. The Jacquards used are heavy-duty, but similar to those found weaving carpets and intricate home-furnishing fabrics. For most 3-D woven fabrics, the warp yarns are commonly woven from a creel setup instead of from traditional loom beams. This setup affords the freedom for each warp yarn to be tensioned individually throughout the weaving process. Individual tension of the warp yarn is necessary, given that many are likely to travel different lengths while weaving distinctive paths through the fabric's thickness, compared with those of their respective warp neighbors that may be weaving entirely different paths.
Combining recent improvements in weave design tools with individual tensioning and Jacquard head control of each warp yarn not only creates numerous possibilities for the design engineer, but also provides the freedom to incorporate a number of different yarns and yarn systems into the 3-D woven structure. Theoretically, it is possible, though probably not practical, to use a different yarn type for each of the warp ends in a 3-D woven fabric. It should be noted that in part because of the extensive setup and yarn-handling requirements, 3-D weaving does result in relatively higher weaving costs than traditional 2-D weaving. In many applications, however, the higher incurred 3-D weaving costs can be offset by reduced lay-up complexity and material handling time, and improved product performance.
Growing Range Of Possibilities
Given the fact that a design engineer now has access to vastly improved design technology and the added depth component of a 3-D woven structure, a wide variety of simple to rather complex shapes can be created. The growing array of 3-D woven fabric possibilities tends to fall into one of two categories: billets and fabric panels; or complex near net-shape preforms.
Billets or flat panels of consistent thickness can be as thin as 0.125 inch (3 millimeters [mm]) or as thick as 5 inches (125 mm) or more. When molded and shaped, these are used in various applications in which delamination is a concern, as structural components and possibly as replacements for heavier metallic versions. 3-D woven billets also are being evaluated in advanced ballistic armor applications, in which their inherent resistance to delamination, improved damage tolerance relative to 2-D laminated structures and significant weight savings show great promise.
Near net-shape preforms can have rather complex geometries tailored to specific applications including airfoils, fan blades, radomes, tubes, bifurcated shapes, contours and structural cross sections such as T's, Pi's and X's. Many are made from ultra-high-performance fibers and used in extreme high-temperature applications in which traditional metals are not able to withstand the operating environment. Other applications include unique cross-section components that help to improve joint strength for composite assemblies. For these applications, the flexibility of 3-D weaving allows for the orientation and positioning of fiber paths that are more in line with physical stresses, resulting in improved product design and efficiency.
It should also be noted that in many 3-D woven preforms, when compared to 2-D laminates, there is generally a trade-off of in-plane strength for through-thickness strength. As a result, each potential 3-D woven application should be evaluated specifically for that application's performance requirements. 3-D woven composite applications and their performance attributes will be discussed in more detail in part two of this series, which will be published in the next issue of Textile World.
Manufacturers of 3-D woven fabrics stand at the ready to assist engineers and developers with new applications for 3-D weaving technology.
Editor’s note: Jim Kaufmann is a senior engineer at TEAM Inc., Woonsocket, R.I., specialists in textile engineering and weaving fabrics and preforms from high-performance, difficult-to-handle fibers including carbon, glass, aramids and ceramic fibers.