Failure mechanism maps for ultra-high molecular weight polyethylene fibre composite beams impacted by blunt projectiles

INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES

卷:178

Article

Liu, B. G.¹  Wadley, H. N. G.²  Deshpande, V. S.¹ 

[1] Univ Cambridge, Dept Engn, Trumpington St, Cambridge CB2 1PZ, England

[2] Univ Virginia, Sch Engn & Appl Sci, Dept Mat Sci & Engn, Charlottesville, VA 22904 USA

关键词: Fibre composites;    Ballistic resistance;    Failure mechanism maps;   

DOI  :  10.1016/j.ijsolstr.2019.07.001

来源: Elsevier

【 摘 要 】

The mechanisms via which failure is initiated in [0 degrees/90 degrees](n) ultra-high molecular weight polyethylene fibre reinforced composite beams during impact by cylindrical projectiles is investigated using detailed finite element (FE) calculations. Each ply of the beam is discretely modelled using a pressure-dependent crystal plasticity framework that accurately accounts for both the large shear strains and fibre rotations that occur within each ply. These FE calculations were used to construct failure mechanism maps for a range of impact velocities, beam shear strengths and ply tensile strengths. Two dominant failure mechanisms emerged from the study: (i) Failure of plies immediately under the projectile via predominantly an indirect tension mechanism in which compressive stress imposed normal to the plies by the projectile induces tensile in-plane ply strains due to the anisotropic plastic expansion of the alternating 0 degrees/90 degrees plies. This is referred to as mode I failure. (ii) Failure due to tensile fibre straining at the rear of the impacted beam resulting from beam bending and accompanying ply stretching. This is referred to as mode II failure. The mode I indirect tension failure mode is dominant at low shear strengths while mode II failure dominates at high shear strengths. The simulations show that low beam shear strengths help relax tensile stresses within the beams, and this typically results in the need for a higher impact velocity to initiate failure. The calculations thus give a mechanistic understanding of experimental observations that have shown low shear strength composites possess a superior ballistic performance. The failure mechanism maps also reveal the existence of an optimal shear strength at which the velocity required to initiate failure is maximised: this optimal shear strength increases with increasing tensile fibre (or ply) strength thereby suggesting a route to developing composites that might serve as structural armours. (C) 2019 Elsevier Ltd. All rights reserved.

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