An analysis of the potential for gravity-induced grading in epoxy interlayers in ceramic armours

Functionally graded materials (FGMs) have great potential in controlling the passage of shock through them and in the distribution of energy through an adhesive interlayer. An adhesive FGM with specific 'grades' to match both the adherend acoustic impedances could prevent the passage of a destructive tensile wave through an armour system, ensuring the ceramic outer layer remains intact and overmatches an incoming projectile for a greater duration prior to failure. However, as FGMs are typically complex and challenging to create, they are often costly and are rarely considered for use in vehicle armours. Gravitational settling of dense powdered particles inside a comparatively viscous epoxy creates an adhesive solution that contains various but predictable quantities of powder at different layers, creating a cheap and controllable FGM. Manipulation of this process through varying powder percentage volumes, alternative materials, powder characteristics and epoxy choices allows for a wide range of FGMs to be created, providing a solution that can be applied to a range of adhesive solutions where shockwaves are a threat. Non-destructive characterisation of the created FGM can be achieved through ultrasonic testing, CT scanning and x-ray radiography. Destructive sectioning of the FGM provides further confidence in the characterisation of the gravitational segregation within the regions with a greater volume of tungsten particles present. Understanding the FGM allows for simulations to be validated, enabling the future rapid determination of the optimum FGM solution with any combination of materials, saving time and money through reducing experimental setups.