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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bilayers was carried out by Roland et al. (2013). A large range of metallic substrates was considered in their study, with substrate thicknesses ranging from 2 mm to 13 mm. The effect of substrate hardness and coating thickness on the coating effectiveness was demonstrated and coupling of the coating performance to the mechanical properties of the substrate was suggested. The decrease in the ballistic limit of thin substrate laminar plates was highlighted in their results, as compared to thicker substrate counterparts. The goal of this study is to gain a thorough understanding of the ballistic response of polyurea-aluminium laminates with thin substrates based on numerical analyses. In the next section a brief description of the constitutive modelling approach is provided for the two materials under consideration followed by the discussion of the nature and configuration characteristics of the in-silico work. The ultimate outcome of such analyses of impact response realisation is the elucidation of predictive mechanisms in ballistics of laminate plates. 2. Material and main methodology This section presents the constitutive descriptions for polyurea and aluminium, together with detailed description of the modelling approach. 2.1 Constitutive description of polyurea The microstructure of polyurea was well documented in the literature (Rinaldi et al., 2011; Runt et al., 2015). It consists of segmented soft and hard domains, which interaction affects its macroscopic mechanical behaviour. Under external load, different microstructural features contribute to the elastic energy and energy dissipation in the material. Elongation of hard segments and soft segments containing polymeric chains, together with stretching of hydrogen bonds and chain interactions, contribute to the elastic response of polyurea. Irreversible energy dissipation occurs due to segmental disintegration and hydrogen-bond breakage. Viscous flow is expected due to friction between chains in the soft domain. Macroscopically, these mechanisms lead to hyperelastic behaviour characterised by rate- and temperature-dependent dissipating characteristics, as indicated in the stress-strain response in Fig. 1a.

Fig. 1. (a) Comparison between experimental (line) and numerical (dotted) results of uniaxial tension and unconfined uniaxial compression of polyurea at various strain rates. (b) Schematic of constitutive model proposed for polyurea. Experimental results are based on the work by Choi et al. (2012).