Ballistic impact on multi-layered ceramic armour: a numerical study of adhesive effects

<p dir="ltr">The high-velocity impact (100-1000 m/s^-1) of multi-layered ceramic armour is modelled numerically with a particular focus on high strain rate behaviour of adhesives. This work aims to enhance the understanding of the physical behaviour of multi-layered armour systems, aid in designing armour against small arms fire, and examine how adhesive selection influences stress wave reflection and transmission at interfaces. A robust, validated, numerical modelling methodology is developed using LS-DYNA to simulate the high-velocity impact of multi-layered ceramic armour with epoxy and silicone adhesives, capable for use with limited computing power such as a desktop PC. To the author's knowledge, this is the first published numerical study of its kind. Novel material model parameters for silicone adhesives at high strain rates are introduced. The essential role of the adhesive selection in ballistic impact is demonstrated numerically for the first time. Additionally, the study reveals the effects of stress wave propagation and interference within armour systems.</p><p dir="ltr">To avoid mass loss, accurately simulate inertial forces and momentum conservation, and model debris fields, hybrid Lagrange-smoothed particle hydrodynamics (SPH) techniques are used. Lagrangian elements decompose into SPH particles to prevent severe mesh distortion, which often occurs during high velocity impact and adversely affects solution accuracy and stability. This methodology is validated through comparison with experimental results from monolithic and bilayer plates. Modelling of split Hopkinson pressure bar (SHPB) tests is used to validate material models for epoxy adhesive and develop novel material model parameters for silicone adhesive.</p><p dir="ltr">Ballistic impact testing using a light gas gun at Loughborough University provides validation cases for the methodology. Layered samples of alumina ceramic and aluminium, bonded with different thicknesses of epoxy or silicone adhesive, are tested. Simulations of these experiments demonstrate the full capability of the methodology to capture the effects of different adhesives, including visualisations of impact progression and initial stress wave propagation with transmission and reflection at interfaces. A well-correlated result is achieved for modelling epoxy at a suitable thickness for armour, however, limitations in the material model for silicone adhesive at the highest strain rates are identified. The expected trend in results when comparing epoxy to silicone is present, confirming the effectiveness of the approach.</p><p dir="ltr">The key limitations lie in the developed silicone material model, particularly due to the absence of a damage model and the limited range of strain rates used in its development from available SHPB test data. Further material testing and model development for silicone would enable the methodology to accurately predict armour performance with silicone adhesive.</p><p dir="ltr">This research lays the foundation for more accurate and reliable designs of multi-layered armour systems, particularly those involving silicone adhesives. By developing a robust numerical modelling methodology, the findings contribute to a deeper understanding of how adhesive properties influence armour performance, which can directly inform future materials engineering and armour design strategies. The potential applications of this work extend to both military and civilian sectors, where improved ballistic protection is crucial. In particular, the methodology developed in this study could lead to enhanced armour systems that are more cost-effective, durable, and efficient in real-world applications. Additionally, the novel insights into adhesive behaviour at high strain rates open new avenues for research into advanced materials for a wide range of protective technologies.</p>