Examining the Relationship Between Ballistic and Structural Properties of Lightweight Thermoplastic Unidirectional Composite Laminates
Abstract : The pursuit for lightweight personal protection (helmets, body armor, etc.) has been a key issue for the Army in recent years. Previous efforts have shown that the variation of orientation and architecture in ultra-high molecular weight polyethylene (UHMWPE) composite panels can significantly affect ballistic performance characteristics. In our experiments, an architecture now referred to as ARL X Hybrid emerged as the clear leader in the compromise between ballistic performance and back face deformation (BFD). For this work, thermoplastic unidirectional materials (both aramid and polyethylene based) were evaluated using 17 grain FSP V50 and 9 mm BFD testing in both typical ([0 deg/90 deg]) and X Hybrid architectures, at an areal density target 27% lighter (7.8 kg/sq m) than the currently fielded state of the art. Digital Image Correlation (DIC) was employed to characterize the materials during testing and to help elucidate the panel response as a function of architecture. Polyethylene materials in the X Hybrid architecture were shown to retain 96-99% of the [0 deg/90 deg] architecture's V50 ballistic performance, while also reducing the BFD by 36-41%. Higher fiber involvement, increased interaction area, and increased membrane stress and through-thickness compression are proposed as factors for this phenomenon.
Materials, manufacturing, and enablers for future soldier protection
The traditional approach for advancing soldier protection has historically relied on a balance of materials and design with knowledge and characterization of the types of threats likely to be encountered. While this approach is still viable and indeed encouraged, future trends advocate for a more aggressive and comprehensive assessment that informs the development of materials in new and strategic ways. In this context, protection (and materials that enable protection) is part of a broader “survivability” perspective, and soldier survivability, mobility, and lethality are linked in a dynamic and evolving relationship. This linked relationship can thus influence materials across multiple length scales and challenge material developers to conceive of mass-efficient multifunctional materials that not only resist ballistic penetration, but mitigate transmission of adverse stress waves, store energy, enable situational awareness, and so on. Equally important are the advances in other technology areas, such as exoskeleton development and the exploitation of robotic and autonomous systems to augment soldier protection and performance. Both exoskeleton and autonomous ground and air platforms enable unprecedented potential to “unburden the soldier” while providing entirely new modes of enhancing soldier survivability and mobility. The materials opportunities are largely undefined for autonomous systems, and as such present exciting incentives for the academic, industrial, and government research communities to develop and deliver new, disruptive capabilities to ensure soldier survivability in the face of evolving threats and future operational environments.
Ballistic impact of fibre composite armours by fragment-simulating projectiles
Tests have been conducted in which 1.1 g fragment-simulating projectiles (FSPs) were fired at nylon 6,6/ ethylene vinyl acetate composite laminates. The laminates were manufactured at two pressing loads and two values of areal density (mass per unit area). V50 penetration velocities were measured and microscopic examination was conducted to gain an insight into the mechanics of penetration. This showed that the penetration is initiated by a combination of shear cutting and tensile failure that can be related to the shape of the FSP. The subsequent phase of penetration involves delamination of the composite and tensile failure of the fibres. There is a trend for laminates manufactured at a lower pressing load to absorb more impact energy.