Even when an armor plate or soft armor panel is entirely composed of ultra-high molecular weight polyethylene (UHMWPE), such as Adept Armor‘s ultra-light and modular Storm Foundation plate, it is still classified as a composite armor plate.
A composite, in technical terms, is a unified material created from two or more distinct constituent materials. UHMWPE fibers, similar to components made from fiberglass or carbon fiber, are always embedded within a polymer resin. These materials are categorized as fiber-reinforced plastics, where the resin acts as the plastic and plays a critical structural role.
Storm Foundation Armor Plate by Adept Armor
In ballistic systems utilizing UHMWPE, the resin serves several key functions:
- Providing stiffness
- Enhancing heat resistance and damage tolerance
- Improving abrasion resistance and mechanical durability
- Securing UHMWPE fibers to prevent them from sliding past one another upon impact
The last point is particularly significant because, unlike aramid fibers, UHMWPE fibers have an extremely low coefficient of friction and can easily slip when subjected to high strain rates during impacts or compressions.
This issue was identified through experience—woven UHMWPE fibers without a resin binder were once used in soft armor panels but delivered poor and unreliable performance. The fibers stretched upon impact, allowing bullets to penetrate through gaps, resulting in significant product failures. The inclusion of a resin binder would have mitigated this fiber slippage.
Resins are crucial overall, but the choice of specific resins differentiates various grades of UHMWPE, influences their selection, and determines their performance characteristics. A study conducted by the U.S. Army Research Laboratory at Aberdeen highlights this distinction.
U.S. Army Research Laboratory Testing
The study analyzed two types of UHMWPE composite panels with identical fiber types and fiber-to-resin ratios. Despite these similarities, differences in resin matrices produced distinct performance outcomes.
Panels with a stiffer resin matrix demonstrated reduced backface deformation (BFD), approximately 25% lower than panels with a more ductile resin matrix. Conversely, the more ductile resin absorbed impact forces better and achieved approximately 5% higher ballistic performance, as measured by V50 velocity.
Researchers also examined a self-reinforced UHMWPE composite made from extruded ribbons bound with a polymer of the same material. This composite exhibited 20 times higher in-plane shear stiffness than the fiber-reinforced panels but had lower strength and modulus, leading to inferior ballistic performance. However, it achieved lower BFD than the fiber-based composites.
These results highlight how resin matrices significantly influence UHMWPE composite performance, affecting energy absorption, deformation, and stiffness. Performance variations depend on threat type, system configuration, and processing methods, making broad generalizations challenging.
