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Concrete is a brittle material, especially under tension. Intensive researches have been reported to add various types of fibres into concrete mix to increase its ductility. Recently, the authors proposed a new type of steel fibre with spiral shape to reinforce concrete material. Laboratory tests on concrete cylinder specimens demonstrated that compared to other fibre types such as the hooked-end, deformed and corrugated fibres the new fibres have larger displacement capacity and provide better bonding with the concrete. This study performs drop-weight impact tests to investigate the behaviour of concrete beams reinforced by different types of steel fibres. The quasi-static compressive and split tensile tests were also conducted to obtain the static properties of plain concrete and steel fibre reinforced concrete (FRC) materials. The quasi-static tests were carried out using hydraulic testing machine and the impact tests were conducted using an instrumented drop-weight testing system. Plain concrete and concrete reinforced by the commonly used hooked-end steel fibres and the proposed spiral-shaped steel fibres were tested in this study. The volume dosage of 1% fibre was used to prepare all FRC specimens. Repeated drop-weight impacts were applied to the beam specimens until total collapse. A 15.2 kg hard steel was used as the drop-weight impactor. A drop height of 0.5 m was considered in performing the impact tests. The force-displacement relations and the energy absorption capabilities of plain concrete and FRC beams were obtained, compared and discussed. The advantage and effectiveness of the newly proposed spiral-shaped steel fibres in increasing the performance of FRC beam elements under impact loads were examined.

Studies of strain gradient plasticity theory have achieved considerable achievements in recent years. However, the combination of the mechanisms of the pressure-sensitive yielding and the size dependence of plastic deformation still remains an open challenge, especially in the relevant numerical simulation. In this paper, the finite-element formulation based on the flow theory of MSG plasticity for pressure-sensitive materials is set up. The elastic indentation response of the single crystal copper is computed using a user-defined eight-node isoparametric element through the USER-ELEMENT interface supported by the commercial software ABAQUS. The results of the numerical simulation show that the indenter load and the hardness have been slightly enhanced when the strain gradient is taken into account, compared to the results obtained from the CAX8R element.