Development and Testing of Advanced Cork Composite Sandwiches for Energy-Absorbing Structures.

Paweł Kaczyński,Fábio A O Fernandes,Mariusz Ptak,Ricardo J Alves De Sousa,Johannes Wilhelm,Leszek Chybowski

doi:10.3390/ma12050697

Abstract

Cork is a sustainable material with remarkable properties. In addition to its main application as wine stoppers, it has also been employed as a sound and thermal insulator in facades, building roofs, aeronautical applications, and, more recently, in impact energy absorption systems. In its natural form, cork is mainly used in wine stopper manufacturing, but for other applications, cork compounds are usually employed, which makes it possible to manufacture complex geometries with nearly isotropic behavior. In this work, an attempt was made to merge the desirable properties of two different cork materials (agglomerated and expanded black) into cork composite sandwich structures. These structures were tested according to impact conditions typically experienced by energy-absorbing liners used in personal safety devices. Additionally, the performance dependency on the working temperature was analyzed. The sole black, expanded cork (EC159) and agglomerated cork (AC199A and AC216) were tested in 500 J impacts. It was found that black cork was characterized by superior thermal stability, while expanded cork allowed absorbing high energies. In the second stage, the composites consisting of both tested materials were tested in 100 J impact scenarios. The combination of two materials of different properties enabled reduction of the peak force exerted on a helmet user’s head during the impact by about 10% compared to agglomerated specimens. Additionally, it was proved that there was no influence of the glue used to join different cork types.

Highlights

Many human activities carry a high risk of hard impacts and require the responsible use of special safety equipment
In addition to testing the specimen out of one micro-agglomeration, the authors decided to examine a combination of different cork materials and selected five different cork types based on the knowledge acquired from earlier studies [35,48]
As was previously reported by the authors in [35], the crashworthiness of agglomerated cork is greatly influenced by temperature

Summary

Introduction

Many human activities carry a high risk of hard impacts and require the responsible use of special safety equipment. Cellular materials like foams are well-known for their excellent energy-absorbing capabilities and are commonly used in industry to manufacture passive safety devices [9,10]. When compressed, their cellular structure exhibits elastic and plastic bending and/or crushing of the cell walls [11,12,13]. Their cellular structure exhibits elastic and plastic bending and/or crushing of the cell walls [11,12,13] During this phase, energy can be absorbed at a near-constant stress level (plateau stress). Aside from the absolute amount of energy absorbed, isotropic behavior of a material is preferred to ensure a uniform behavior under varying loads [14,15,16,17]

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Results

Conclusion