How to Improve the V50 Value of Bulletproof Helmets

Core Definition and Industrial Significance of V50 Value The V50 value (Velocity at 50% Probability of Penetration) is a key indicator for measuring the protective performance of bulletproof helmets. It refers to the average velocity at which a projectile of a specific mass penetrates the helmet with a 50% probability. A higher V50 value indicates stronger resistance of the helmet to high-speed impacts.

In accordance with domestic and international standards such as NIJ STD 0106.01 and GA 293, the V50 value requires test conditions to be set based on projectile types (e.g., 9mm Para, 5.56mm SS109) and projectile masses (e.g., 8g, 4.01g). The improvement of the V50 value is directly related to the helmet’s ability to protect the user’s life, making it a core performance assessment indicator in fields such as military and police equipment, and security protection.

Core Technologies for Improving the V50 Value

1、Material System Upgrade: Consolidating the Foundation of Protection Selection of High-Performance Fibers: Priority is given to advanced bulletproof fibers such as ultra-high molecular weight polyethylene (UHMWPE) and aramids (Kevlar, Twaron). Their tensile strength (≥3.5GPa) and modulus (≥120GPa) far exceed those of traditional glass fibers. For example, the specific strength of UHMWPE fiber is 15 times that of steel; it can absorb projectile kinetic energy through fiber fracture and slippage, significantly improving the V50 value. It is recommended to select products with a fiber linear density of ≤1500dtex and an elongation at break of 1.5%-3% to ensure energy absorption efficiency.

2、Optimization of Fiber Pretreatment: Plasma modification and coupling agent treatment (e.g., silane coupling agent KH-550) are used to enhance the interfacial bonding force between fibers and the matrix, preventing fiber-resin detachment during projectile impact and reducing protection failure. After pretreatment, the surface roughness of the fibers should increase by more than 30%, and the interfacial shear strength should be ≥8MPa.

3、Improvement of Matrix Resins: Modified matrices such as epoxy resins and polyurethane resins are adopted, with fillers (e.g., nano-silica, carbon fiber powder) added at a dosage of 5%-10% to enhance the impact toughness and heat resistance of the resin. The resin curing process is optimized (temperature: 120-150℃, pressure: 0.8-1.2MPa) to ensure no pores or delamination inside the composite material.

Structural Design Optimization: Enhancing Energy Buffering

1、Layered Structure Design of Helmet Shell: A "fiber-reinforced composite material + buffer layer + inner liner" sandwich structure is adopted. The outer layer uses 3-5 layers of UHMWPE fiber fabric laminates (fibers arranged in crossed directions, e.g., 0°/90°/45°) to improve penetration resistance; the middle buffer layer uses EVA foam or polyurethane foam (density: 0.3-0.5g/cm³) with a thickness of 5-8mm, which absorbs projectile impact energy through foam compression and deformation; the inner liner uses nylon mesh or sponge with good energy absorption performance, balancing comfort and secondary buffering.

2、Optimization of Curvature and Thickness: The curvature of the helmet shell is designed according to the contour of the human head (top arc radius: 120-150mm, side arc radius: 80-100mm) to avoid concentrated stress when projectiles hit vertically. The thickness of key protection areas (e.g., forehead, sides) is increased by 10%-15%, while the thickness of non-key areas is optimized to control the overall weight (military helmet weight ≤1.8kg).

3、Edge Protection Design: The edges of the helmet shell are treated with edge wrapping (e.g., wrapped with aramid webbing) to prevent fiber cracking at the edges during projectile impact; anti-ricochet structures (e.g., micro-arc edge design) are installed to guide projectile deflection and reduce the penetration probability.