How to Improve the Anti-Dent Performance of Bulletproof Helmets

Core Definition of Anti-Dent Performance and Industry Standards

The anti-dent performance of a bulletproof helmet refers to the ability of the helmet’s shell and inner liner to avoid permanent dents when subjected to high-speed impacts (e.g., from bullets or shrapnel) or blunt force collisions. Typically, the maximum allowable dent depth is ≤15mm, in compliance with standards such as NIJ STD 0106.01 and GA 293. This performance is a critical indicator for measuring the protective integrity of the helmet, as it directly affects the survival probability of the wearer under non-penetrating impacts.

Material Upgrades: Building a Solid Foundation for Anti-Dent Protection

1. Iteration of Shell Materials

High-modulus fiber composites as the preferred choice: Select high-modulus fiber composites such as ultra-high molecular weight polyethylene (UHMWPE) and aramid (Kevlar) fibers of Grade IIIA or higher. Improve impact toughness by increasing the fiber areal density (recommended ≥600g/㎡). These fibers have a breaking strength of over 3.5GPa, which can effectively disperse impact energy and reduce local dents.

Composite ceramic interlayer design: Composite alumina (Al₂O₃) or silicon carbide (SiC) ceramic plates (3-5mm thick) on the inner side of the fiber shell. Leverage the high hardness of ceramics to prevent stress concentration at the impact point, and combine it with the toughness buffering of the fiber layer to form a dual-protection system of "hard resistance + soft absorption".

2. Optimization of Liner Materials

High-density polyurethane (PU) foam liner: Replace traditional EVA materials with high-density PU foam liners (density ≥80kg/m³). With a compression rebound rate of ≥90%, these liners can absorb energy through elastic deformation at the moment of impact, preventing dents on the shell from transferring to the head.

Innovative honeycomb aluminum core structure: Embed aluminum alloy honeycomb cores in the PU liner (honeycomb cell size: 5-8mm; wall thickness: 0.1-0.2mm). Utilize the compressive stability of the honeycomb structure to further disperse impact loads and reduce the risk of local dents.

Structural Design Innovation: Optimizing Force Transmission Paths

1. Optimization of Curved Surface Radius

Adopt a "spheroid-like" design for the helmet shell. Control the curvature radius of the top to 120-150mm and the side curvature radius to 80-100mm. This avoids impact energy concentration caused by flat or small-curvature designs, and disperses energy to the entire helmet shell through curved surface diversion.

2. Multi-Layer Composite Structure

Implement a three-layer composite structure consisting of "shell + buffer layer + inner liner":

The shell is made of fiber-reinforced composite materials;

The buffer layer uses silica gel or butyl rubber (5-8mm thick);

The inner liner is made of PU foam.

The three layers are tightly bonded through a hot-press molding process. By leveraging the differences in elastic modulus of different materials, impact energy is gradually absorbed and dissipated, preventing dents caused by insufficient rigidity of a single material.

3. Edge Reinforcement Design

Add carbon fiber reinforcement strips (15-20mm wide, 2-3mm thick) to the helmet edges. This enhances the edge’s impact resistance, prevents local dents or warping during side impacts, and improves the overall structural stability of the helmet.

Process Improvements: Ensuring the Performance of Materials and Structures

1. Precision Molding Processes

(1) Shell molding: Use compression molding for the shell, controlling the molding temperature at 120-150℃ and pressure at 2-3MPa. This ensures full impregnation of fibers with resin, reduces internal porosity (≤1%), and improves material density—avoiding reduced local anti-dent performance caused by process defects.

(2) Liner molding: Adopt an integrated injection foaming process for the liner to ensure foaming uniformity and eliminate stress concentration points caused by air bubbles or uneven density.

2. Interface Bonding Technology

Use epoxy resin-based adhesives (shear strength ≥15MPa) to firmly bond the shell, buffer layer, and inner liner through hot-press bonding. This prevents interlayer peeling, ensures effective transmission of impact energy between layers, and avoids local dents caused by interlayer loosening.