3-D Weaving: Applications And A Range Of Possibilities
Part two of a two-part series about 3-D weaving and its current and potential applications
There is a growing range of possibilities for 3-D woven fabrics in composite applications. To begin
talking about these applications, it first may be helpful to define the term "composite."
According to Chris Pastore, Ph.D., professor and co-director of the Engineering and Design Institute at Philadelphia University, "composite" is defined as "a product composed of two or more distinct components, one usually being fibrous in nature, that behave as a uniform, monolithic material."
Aaron Tomich, program manager, Woonsocket, R.I.-based TEAM Inc. — specialists in textile engineering and weaving 2-D and 3-D fabrics and preforms — says that development of composite applications often involves collaboration between the end-product customer and the manufacturer: "We work closely with our customers to match the fiber placement and properties of our 3-D woven fabrics with the resin or matrix systems used to ensure that the individual components work together as one in the end-product."
3-D woven fabrics in composite form can be used in a wide range of products and applications.
Several key attributes drive 3-D woven fabric performance and, consequently, its attractiveness for composite applications. Such attributes include:
- inherent delamination resistance;
- improved damage tolerance;
- design flexibility and versatility;
- ability to tailor composite properties to the application;
- near net shape preform capabilities;
- reduced lay-up complexity and handling time; and
- weight reductions vis-à-vis most metal counterparts.
Because the 3-D weaving process is versatile, it can support a wide array of raw materials, weave patterns, shapes, widths and thicknesses. Accordingly, composite applications incorporating 3-D woven structures fall mainly into one of two rather broad categories: woven billets and flat panels; or complex near net shape preforms.
3-D Woven Billets And Flat Panels
3-D woven billets and flat panels, as the names imply, are commonly woven with a consistent thickness and density across their length and width. Woven thicknesses can range from less than 0.125 inches, or 3 millimeters (mm), to 5 inches, or 125 mm, or greater. In general, these fabrics are infused with a resin system and molded, then cut or machined to a desired shape. Applications include precision-machined parts for military, industrial, marine and infrastructure components — typically as replacements for heavier metal versions in applications in which significant weight savings provide additional benefits. The primary drivers promoting 3-D woven composites usage in these applications are their intrinsic delamination resistance and improved damage tolerance. The adverse effects of delamination and the lower damage tolerance of 2-D composite laminates in some applications continue to raise concerns for design engineers.
Two examples of military applications for which 3-D woven composite panels show great promise are heavy-duty ballistic panels for armoring military vehicles and sabots used to fire high-velocity projectiles.
Comparative photos of a 2-D laminated panel (left) and a 3-D woven panel (right) after ballistic testing show a significantly larger damage area, as indicated by the dark gray areas, on the 2-D panel.
Ballistic testing of comparative composite products made from 2-D laminates and 3-D woven panels show the 3-D woven panels to have approximately 5- to 15-percent lower V50 results than 2-D laminated panels for two threat levels and weights studied. A V50 result is derived from a military test procedure that determines the average velocity at which 50 percent of shots pass through and 50 percent are stopped by the armor being tested. However, the quantifiable damage to the 3-D panel was 200- to 300-percent less than that of a comparable 2-D laminate. The 3-D panel is able to absorb the initial shock and dissipate the forces of ballistic impact more efficiently, without the delamination that is observed in 2-D laminate structures. This distinction is important in multi-hit scenarios in which the 3-D panel maintains a greater degree of integrity and is able to perform at a higher level than the 2-D counterpart. The distinction is even more critical in applications in which the composite panel is designed and incorporated to serve in both armor and structural capacities.
For similar reasons, 3-D woven billets are being evaluated for use as sabots in military applications. Sabots are used as a means to increase the muzzle velocity of certain categories of projectiles. The 3-D composite billets, designed and woven to conform to the desired arc shape of the sabot, are relatively lightweight while maintaining the inter-laminar strength and damage tolerance needed to withstand the intense pressure and torsional stresses generated when propelled from a rifled barrel. Next-generation railguns also present similar opportunities for 3-D woven ceramic preforms.
Complex Near Net Shape Preforms
Near net shape preforms are fabric structures designed and woven to a close approximation of the actual final molded composite shape. Given the close approximation of the preform to the final part, machining time, material costs, handling time and subsequent assembly costs can be reduced. Advances in design software, computer-aided-design tools, and finite element analysis are fostering the production of complicated shapes and profiles that feature targeted fiber orientation and application-specific mechanical properties more accurately than in the past. These design tools combined with the flexibility and versatility inherent to 3-D weaving provide the design engineer with a kaleidoscope of options to tailor the shape and properties to each unique application. A variety of shapes can be produced, which, in addition to solid structures such as billets and panels, also include hollow structures, non-linear or shell shapes, and nodal structures, or some combination thereof.
Several manufacturers currently produce an array of cross-sectional weave profiles — such as Pi, T, H, J, L, and others — from high-performance materials, which aid in reinforcing the joints of composite panel assemblies. These 3-D woven preforms can be tailored through fiber orientation and weighting to improve joint strengths and distribute the stress and forces being applied when in use. Additional cross-sectional shapes can be incorporated within joints or other areas as gap fillers to improve integrity and overall performance while also reducing lay-up time, complexity and variability.
High-performance engine components and other aerospace applications also benefit greatly from the use of 3-D woven products. These include vanes and airfoils, fan blades, fan casings and containment systems for several current and future jet engines.
A 3-D woven near net shape preform is prepared for molding to its final shape as a fan blade prototype.
Vanes and airfoils are used within the jet engine to route and compress air through the combustion chamber, thus generating thrust. As with cross-sectionals, these 3-D woven near net shape components can be tailored to target specific properties and profiles for the application. Usually tapered across both the length and width, these preforms provide continuous fibers through the most highly loaded regions of the composite part. There is also the option to weave the airfoil portion as either a solid or a tubular piece, depending on its location within the engine and the performance requirements.
Fan blades are the large blades visible when looking into the front of a jet engine. Historically, these were made from advanced metals including titanium, but 3-D woven composite blades are beginning to gain traction in new programs such as CFM International's LEAP engine series. Plans for this new engine series call for the use of 3-D woven composite fan blades, which are woven to near net shape and incorporate the root structure — the critical portion that anchors the blade to the jet engine's shaft. Because the complete blade and root are integrally woven, threats of delamination due to a bird strike decrease, while improved damage tolerance and weight savings are realized. The fan casing used in the LEAP engine also will be constructed using 3-D woven composites.
Composites incorporating 3-D woven preforms are constantly being developed and evaluated for other jet engine components as well as advanced structural assemblies in the fuselage of new commercial and military aircraft. But if jet engine components aren't quite exciting enough, there are always other military and aerospace applications under development that benefit from 3-D woven product attributes. Items like radomes, missile fins and nose cones are all being developed incorporating 3-D woven products. Or, for those with less military-oriented tastes, 3-D woven structures are beginning to find application in numerous industrial and commercial products as well. These include girders and beams for building construction, components for high-performance boats and race cars, sporting goods, and even biomedical applications for which the physical performance characteristics, design flexibility and versatility of 3-D weaves are being pushed to even higher levels, expanding further a wide range of possibilities.
Editor’s note: Jim Kaufmann is a senior engineer at TEAM Inc., Woonsocket, R.I.