Abstract
Protective structures subjected to intensive loads that may benefit from the use of multilayer composite structures with excellent hardness and impact resistance represent an emerging research field in recent times. In this study, low-velocity projectile impact tests were performed on Functionally-graded Preplaced Aggregate Fibrous Concrete (FPAFC) mixtures to evaluate their performance. The effects of projectile needle type, fibre type and hybridization in addition to the number of layers in the composites on projectile impact were investigated. The bioinspiration of the excellent impact strength of turtle shells was used to design an FPAFC comprising a higher amount of steel and polypropylene fibres at the outer layers. In parallel, one and two-layered concretes were also cast to assess the effectiveness of three-layered FPAFC. The tests were performed on disc specimens using non-deformable compound bevel, convex edge and hollow edge projectiles. The damage severity was quantified by the top damage area, bottom damage area and depth of penetration. In addition, a simple analytical model for predicting the composite mass expulsion was developed and implemented. Findings indicated that regardless of fiber type and distribution, the compound bevel projectile needle produced the lowest impact numbers for all single, double and triple-layer specimens compared to the convex edge and hollow edge projectiles. Repeated projectile impacts increased the penetration depth and damaged area at the top and bottom surfaces of all targets. Targets were more resistant to convex edge and hollow edge projectile penetration than the compound bevel. The experimental and analytical model results for mass expelled from the top surface are reasonably acceptable. This research gives an idea of developing advanced fibrous composite with superior impact resistance for the promising protective structures.
Highlights
Structural composite materials inspired by biology have attracted significant interest in recent times due to their impressive mechanical properties and innovative hierarchical structures [1]
The following points summarize the most important concluding remarks obtained from this research, (1) For fibrous specimens, using the compound bevel (CB) projectile needle resulted in the lowest impact numbers for all single, double and triple-layer specimens compared to convex edge (CE) and hollow edge (HE) projectiles regardless of the fibre type, content and distribution
For the single-layer specimens with 2.4% steel fibre (SF), the recorded impact numbers were 35, 48 and 50 under CB, CE and HE projectile needles, respectively
Summary
Structural composite materials inspired by biology have attracted significant interest in recent times due to their impressive mechanical properties and innovative hierarchical structures [1]. An exceptional amalgamation of biological composite structures (e.g., the turtle shell) with improved mechanical properties can be attained and used for penetration resistance. Depending on the needs of strong composites, the developed concept of functionally graded fibrous concrete intended to deliver a superior impact resistance by changing the properties along the depth of concrete and it can be a suitable candidate to be usefully applied in protective structures. The results indicated that functionally graded slabs containing steel fibres showed very effective resistance to projectile impact compared to traditional fibrous concrete slabs, where the destroyed volume and penetration depth were significantly reduced in functionally graded slabs. The reviewed research results were about the impact properties of fibrous concrete targets against single hits of high-velocity projectiles. A simulation model was used to predict the ejected mass during the penetration and compared with the experimental results
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