Performance Requirements of Metallic Foam Cores for Blast-Resistant Doors

The metallic foam core inside blast-resistant doors primarily functions to absorb detonation wave energy, dissipate impact kinetic energy, provide auxiliary thermal insulation and flame retardancy, and block flying debris generated after an explosion. Nickel-chromium or nickel-chromium-aluminum alloy foam is the preferred material, while pure nickel foam and pure copper foam are not recommended.

Ⅰ. Mechanical Energy Absorption Performance (Most Critical Index)

● High ductility and extended yield plateau: Under blast impact loading, the material shall feature a wide and stable compression plateau to convert most shockwave energy into plastic deformation, rather than undergoing brittle fracture.

● Appropriate porosity and pore size: Excessively large pores lead to insufficient energy absorption; overly tiny pores result in excessive rigidity and poor buffering performance. The typical porosity range is 80% to 92%, striking a balance between energy absorption capacity and structural strength.

● High-speed impact resistance: Capable of withstanding instantaneous high-pressure detonation loads without shattering into secondary fragments that may cause secondary injuries.

● Residual strength after loading: Partial structural integrity shall be retained following blast impact. Even after deformation, the core can still maintain thermal insulation and flame retardant properties.

Ⅱ. High-Temperature Resistance, Ablation Resistance and Fire Safety

● High-temperature oxidation resistance: Explosions generate instantaneous temperatures up to 1000 °C. Nickel-chromium-aluminum based foam forms a dense protective oxide layer at high temperatures to resist melting and burn-through. Pure copper and pure nickel tend to melt under blast fire conditions, making them unsuitable for severe blast-fire service environments.

● Flame quenching capacity: The interconnected porous structure extinguishes flames and prevents high-temperature flue gas and hot gas from penetrating through the door core.

● Thermal shock resistance: Tolerates drastic temperature fluctuations without developing thermal cracks or pulverization.

Ⅲ. Corrosion Resistance & Long-Term Durability

● Resists corrosion from humidity and industrial atmospheres; avoids rusting and pulverization during long-term factory service to prevent performance degradation.

● Anti-aging property: Unlike polymer foams, metallic foams do not harden or degrade over prolonged service life.

Ⅳ. Structural & Machinability

● Easy to cut and form into sheets or assembly blocks for cavity filling inside blast-resistant doors; weldable to prevent detachment under impact.

● Controllable lightweight weight: Low mass avoids overloading door hinges and door frames.

Ⅴ. Auxiliary Functional Properties

● Vibration and noise attenuation: Absorbs equipment vibration and operational noise under normal working conditions.

● Moderate thermal conductivity: Restricts heat transfer through the door body and limits temperature rise on the non-fire side.

Ⅵ. Material Selection Summary

● First choice: Nickel-chromium-aluminum metallic foam, delivering optimal comprehensive performance in blast resistance, high-temperature tolerance and oxidation resistance.

● Alternative option: Nickel-chromium alloy foam.

● Not recommended: Pure copper foam, pure nickel foam; prone to melting under blast-fire conditions with poor reliability.

Note: Higher density does not equal superior performance. Materials with excessively high density become rigid with limited deformability and low energy absorption capacity; excessively high porosity triggers premature structural collapse. Porosity and thickness shall be matched according to the specified blast-fire pressure rating.