PSI - Issue 28

Theodosios Stergiou et al. / Procedia Structural Integrity 28 (2020) 1258–1266 T. Stergiou et al. / Structural Integrity Procedia 00 (2019) 000–000

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Nomenclature ∗

� � � F H ℎ � ℎ � I J � � � ∗ � Λ r W

distortional component of the left Cauchy-Green tensor

projectile diameter

total Hencky strain tensor

Hencky strain tensor of the elastic component

factor of sensitivity to triaxiality

factor accounting for flow network dependency

deformation gradient matrix

target plate height substrate thickness coating thickness identity matrix

Jacobian of the deformation gradient parameter dependent of stress triaxiality

target plate width

viscoplastic flow component

the von Mises strain of the viscous component

bulk modulus

polymer-chain stretch limiting chain stretch applied chain stretch Langevin function

shear modulus

� � �� � � � dev[ ]

Cauchy stress tensor

reference von Mises stress tensor at failure von Mises stress tensor at failure

applied shear stress tensor deviatoric component of a tensor

A , a , B , C , � , � , material model parameters , , ̂ , ̂ , ��� , ��� 1. Introduction

Lightweight structural components with high impact resistance are required in many industries. The use of polymeric materials as front impact layers applied to existing components can offer additional energy-absorbing capabilities thanks to energy dissipation through viscous and plastic deformation, inherent to such materials while taking advantage of their relatively low density. In this study, the response of thin aluminium plates with a polyurea as a frontal impact layer subjected to dynamic loading condition is investigated. Polyurea is a polymer consisting of two domains - harder and softer - and a member of a broader class of polymers named segmented copolymers . The material’s stress-strain response demonstrates an initial hyperelastic behaviour, followed by plastic deformation characterised by hardening that is rate- and temperature-dependent with tension-compression asymmetry. Distinct cyclic softening (Mullins effect) is also observed during loading and unloading cycles, resulting from breakage of hydrogen bonds and disintegration of the hard domain. Such characteristics are desirable for dynamic and ballistic applications. For these reasons, this area of research was revitalised in the past fifteen years (Amini et al., 2010; Boyce et al., 2000; Roland & Giller, 2015; Roland et al., 2010). Due to the contradictory observations in studies of multi-layer target configurations (Almohandes et al., 1996; Corran et al., 1983; Marom & Bonder, 1979), and the multi-parametric nature of impact, generalisation of its dynamic response remains a challenge. The first experimental study on the ballistic behaviour polyurea elastomer/metal