Comparative numerical studies of projectile impacts on plain and steel-fibre reinforced concrete

Abstract

The enhanced energy absorption characteristics of fibre-reinforced concrete, compared to plain concrete, has in experimentally studies been shown to improve the projectile resistance and motivate its increased usage in protective structures. However, the high cost of undertaking experiments and the high parameter variation and dependency of the experimental setups and results, respectively, make it difficult to draw generic conclusions of how the addition and increased amount of fibres affects the local damage caused by projectile impact, which motivates the use of numerical simulations to study this. The numerical hydrocode AUTODYN was used in a qualitative study of how the addition of different amounts of fibres, modelled as different post-crack relations, influence the depth of penetration and crater formation on the front and rear face of a concrete target. Fibres added to the concrete mix had a minor influence on the depth of penetration while the crater size on both front and rear faces of the target decreases. The crack propagation beyond the crater on the front face was also reduced when fibres were added to the concrete. An increased amount of fibres in the concrete showed no effect on the size of the front-face crater, but led to further decreased size of the crater on the rear face of the concrete cylinder. It is concluded that the scabbing crater can be reduced in size and prevented by usage of fibre-reinforced concrete even if the depth of penetration is only slightly less than to penetration depth in plain concrete.Keywords: Numerical simulation, Projectile impact, Steel-fibre reinforced concrete, Penetration 1.Introduction A projectile impact may cause local and global damage to a concrete structure. Global damage consists of flexural deformations, which, unlike local damage, may cause structural failure. Local damage may cause spalling and crushing of concrete on the front face and scabbing on the rear face of the target, together with projectile penetration into the target or even full penetration (i.e. perforation) of the target [1,2]. Different variables have been proposed to measure local damage, such as depth of penetration, perforation and scabbing thickness or ballistic limit (i.e. the minimum velocity at which the projectile penetrates the target) in plain or reinforced concrete [2].Researchers have experimentally studied the behaviour of fibre-reinforced concrete under impact loading and observed a significant increase in the overall resistance to local damage when compared to plain concrete [3][4][5][6][7][8][9][10][11]. However, the structural behaviours of targets subjected to impact are complicated, depending on material factors as well as test-condition factors [6], which vary between the reported experiments and therefore make it difficult to draw generic conclusions of the effect of fibres and how it changes with different amounts of fibres in the concrete.The local damage parameters in concrete are often estimated by using empirical, semi-empirical or purely analytical eq...

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