Numerical simulation of the shock spalling failure of bonded fibre–epoxy strengthening systems for metallic structures

• Shock spalling of bonded strengthening systems for metallic structures are considered.
• FE models of shock spalling of fibre–epoxy systems are validated against experiments.
• Models then consider other blast environments, geometric and material properties.
• Iso-damage curves of shock spalling damage and failure are provided for design.

Fibre–epoxy strengthening systems have been identified as a suitable approach for metallic structures subjected to explosive loads, to increase the structural performance of existing structures and/or create high performance hybrid structures. However, experimental studies have shown that when subjected to the blast pressures resulting from the detonation of explosives, the epoxy bond material may fail by shock spalling, substantially reducing the performance of the strengthening system. Shock spall failure involves tension fracturing of the epoxy material, resulting from tension stress waves generated as the shock wave moves through the composite structure, creating wave reflections and interactions at the constituent boundaries. The experiments investigated a limited range of blast environments due to the limitations of laboratory testing. The present study validates numerical models of the experimentally observed shock spalling failures, and then extends the models to investigate the effect of a broad range of blast environments, metal geometric and material properties, epoxy bond material properties and fibre layouts on the shock spalling failure of the epoxy bond. The numerical results are used to provide generalised considerations for the design of bonded fibre–epoxy strengthening systems for metallic structures, in the form of iso-damage curves for the spall damage and spall failure of such systems in a variety of practical blast environments.