Stress wave attenuation in ultra-high performance fibre-reinforced concrete during ballistic impact

Depending on material properties and boundary conditions, various waves propagate within the target, during an impact event. Stress wave attenuation during ballistic impact can be expressed in strain profiles regarding time and distance from the impact point. The design of a ballistic-resistant structure thus depends on the stress wave attenuation. This present study focused on stress wave attenuation under projectile impact in ultra-high performance fibre-reinforced concrete (UHPFRC). 3 mm strain gauges were found suitable for such measurements. Two different types (steel fibres) of UHPFRC (Single fibre (S2): 2 % of 6 mm steel fibre and Hybrid fibre combination (S0.5L1.5): 0.5 % of 6 mm + 1.5 % of 13 mm steel fibres) were used for investigation. During the ballistic impact event, strain profiles at specific distances from the point of impact on both the front and rear surfaces of UHPFRC targets were recorded. The scabbing damage due to tension was captured and analysed in this study through stress wave attenuation. The impact performance of hybrid (Short and Long fibres) S0.5L1.5 UHPFRC combinations was much better than S2 (only short fibres) UHPFRC targets. The hybrid steel fibre UHPFRC also shows higher strain attenuation (than short fibre based UHPFRC) in the range of 10-30 µε/mm. It was concluded that the efficiently designed ballistic-resistant UHPFRC should have higher wave attenuation, implying the concrete has enhanced capacity to absorb and localise energy, thereby mitigating the extent of damage inflicted upon the overall concrete slab.