Influence of Thermal Shocks on Residual Static Strength, Impact Strength and Elasticity of Polymer-Composite Materials Used in Firefighting Helmets.

Daniel Pieniak,Jarosław Selech,Marcin Oszust,Renata Kamocka-Bronisz,Robert Piec,Grzegorz Dzień,Krzysztof Przystupa,Dariusz Ulbrich,Agata Walczak

doi:10.3390/ma15010057

Abstract

The article presents results of experimental studies on mechanical properties of the polymer-composite material used in manufacturing firefighting helmets. Conducted studies included static and impact strength tests, as well as a shock absorption test of glass fiber-reinforced polyamide 66 (PA66) samples and firefighting helmets. Samples were subject to the impact of thermal shocks before or during being placed under a mechanical load. A significant influence of thermal shocks on mechanical properties of glass fiber-reinforced PA66 was shown. The decrease in strength and elastic properties after cyclic heat shocks ranged from a few to several dozen percent. The average bending strength and modulus during the 170 degree Celsius shock dropped to several dozen percent from the room temperature strength. Under these thermal conditions, the impact strength was lost, and the lateral deflection of the helmet shells increased by approximately 300%. Moreover, while forcing a thermal shock occurring during the heat load, it was noticed that the character of a composite damage changes from the elasto-brittle type into the elasto-plastic one. It was also proved that changes in mechanical and elastic properties of the material used in a helmet shell can affect the protective abilities of a helmet.

Highlights

According to the Directive 89/656/EEC [1] that defines the main design, technological and maintenance rules of personal protective equipment, a firefighting helmet is a piece of personal protective equipment that is to protect health and provide safety at the highest possible level
Considering the above and the fact that there have been few studies concerning damages that occur during the maintenance of firefighting helmets, the test results presented in the article are of great significance; 2
Thermal shocks in the extent compatible with thermal hazards that occur during fire and rescue operations cause significant changes in strength and elastic properties of the composite that the studied helmet is made of

Summary

Introduction

According to the Directive 89/656/EEC [1] that defines the main design, technological and maintenance rules of personal protective equipment, a firefighting helmet is a piece of personal protective equipment that is to protect health and provide safety at the highest possible level. Regulations concerning firefighting in Poland and other European countries allow using Type-B EN 443 helmets [2]. Such helmets are supposed to protect the head and the neck of a firefighter. The superior function of a firefighting helmet is to absorb the mechanical impact that the firefighter’s head is exposed to, redistribute absorbed kinetic energy from the direction that constitutes the greatest danger, and, in turn, to dissipate it in a way that does not cause any excessive harm to a firefighter and, if possible, does not damage a helmet itself [3]. The main role of a helmet is to protect a firefighter against mechanical risks that occur during firefighting operations and action exercises. A dynamic load is related to a short and impulsive impact of a large amplitude [5]

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