Processing and Cutting of Low-Modulus Aramid (e.g., R&G Aramid Fabric Ballistics): Challenges and Recommendations

Low-modulus aramid fibers, such as those used in protective clothing (e.g., bulletproof vests, helmets, motorcycle clothing) and hard ballistics, are characterized by their high toughness and flexibility. These properties make them particularly resistant to abrasion and offer high elongation at break while maintaining a low tensile modulus. However, these fibers are more difficult to process than high-modulus aramids, presenting several technical challenges.

Challenges in Processing

The processing of low-modulus aramid laminates can be problematic due to poor resin uptake and the dense structure of the fabric. Aramid has a lower adhesion to resins, resulting in weak bonds between the layers. This makes laminating difficult, and the materials are prone to delamination at the edges, especially during mechanical cutting processes.

Another issue arises when cutting: attempting to cut low-modulus aramid with a circular saw yields poor results. The material is hard to control, and the cut edges tend to fray or splinter. Much better results are achieved with an oscillating saw, as the non-rotating motion of the blade reduces fraying and creates a cleaner edge.

Recommended Cutting Methods

1. Oscillating Saws: These are particularly well-suited for cutting aramid laminates because they provide smooth cutting action without the risk of "over-turning" the blade. This reduces fraying at the edges and minimizes the risk of delamination.
2. Water Jet Cutting: This method is particularly effective for cutting aramid laminates cleanly and precisely. The water jet produces a clean cut without fraying or delamination and can handle materials up to about 10 mm thick with ease.
3. Laser Cutting: For laminate thicknesses up to 10 mm, laser cutting can be a good option as it allows for precise cuts. However, high temperatures can affect the material structure, potentially causing changes to the cut edges. For thicker laminates, water jet cutting is generally preferred.
4. Mechanical Processing: When using circular saws or other rotating tools, special precautions should be taken, such as reducing the speed to protect the material. These methods are less suitable and can lead to heavily frayed edges and delaminations.

Additional Notes on Adhesion and Delamination

The low adhesion of low-modulus aramid to resins is another challenge in processing. Ballistic fabrics are woven very densely to prevent penetration (e.g., by projectiles). However, resins do not adequately impregnate the layers, and the individual fibers are not fully surrounded by resin. The interlayer adhesion is therefore relatively low, and under high stress, the layers may delaminate. Our own experiments showed that although laminate exhibited delaminations during ballistic testing, it still reliably stopped projectiles of various calibers.

Depending on the application, preliminary tests are absolutely necessary. A general statement cannot be made, as besides the projectile speed, factors such as caliber, shape, and material of the projectile play a significant role. Small calibers with high velocity and hard projectile materials penetrate more easily than, for example, copper-coated lead projectiles in calibers like 9 mm, .40 S&W, or .45 ACP.

Conclusion

Despite the challenges in processing, low-modulus aramid remains a preferred material for many applications in soft ballistics and protective clothing due to its toughness and flexibility. The choice of the right cutting technique, such as using oscillating saws, is crucial to fully exploit the benefits of aramid laminates in practice.