Energy absorbing characteristics of carbon fiber sandwich composites with all-natural expanded cork core

Abstract

Natural and environmentally friendly composite materials are becoming more popular due to growing ecological and energy concerns. Expanded cork agglomerate is a 100% natural agglomerate structure created by heating cork bark granules with superheated steam while under pressure. This study investigates the use of expanded cork as a core material in sandwich composite structures. Sandwich composite structures are used in a great number of applications ranging from aerospace to athletic equipment. They are known for being strong, stiff and lightweight. However, they often fare poorly when it comes to energy absorption and dissipation, particularly in acoustics, vibrational damping, and impact. This study investigates the energy absorbing performance for sandwich composites with carbon fiber face sheets and an expanded cork core by comparing it to Rohacell 110 IG, a synthetic, cellular, polymethacrylimide (PMI) foam used often as a core in material in high-performance composites. Characterization is done on composite structures with both types of cores in acoustics, vibrational damping, and low velocity impact. To better understand the core materials themselves, the viscoelastic response of the core materials is then characterized using static and dynamic testing methods. The viscoelastic responses of the core materials are then used to model the energy absorption in sandwich composites using existing analytical models. It was observed that expanded cork core sandwich composites showed significantly increased energy absorbing capabilities including noise, vibrational damping and low-velocity impact resistance over the synthetic foam. This was determined to be a result of the viscoelastic damping and recoverability seen in the core material. The increase in energy absorption makes expanded cork an attractive all-natural replacement for synthetic foams in sandwich composites.