PSI - Issue 37

Theodosios Stergiou et al. / Procedia Structural Integrity 37 (2022) 250–256 T. Stergiou et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Nomenclature cross- sectional area of projectile’s shank H target height ℎ target thickness projectile ’s effective length (when constant volume and shank cross-sectional area are assumed) ( /2)/cot⁡( ̂) , projectile’s nose length , projectile mass target resistance target’s dynamic yield strength W target width W work in eroding the target work in forming an opening in the target equal to the projectile’s cross -section ̂ Impact with plate-like projectiles with high-aspect-ratio cross-sections is known to occur, e.g., in cases of windborne debris, secondary impacts of fractured material, and containment applications. Yet, only limited research was conducted in this area (Pereira et al., 2014; He et al., 2016; Naik et al., 2009; Liu et al., 2021), since most studies concentrate on axisymmetric impactors due to their direct applicability in the military sector and higher flight stability during testing. The goal of this study is to examine the effect of nose geometry on the capability of sharp plate-like projectiles to penetrate a thin AlMg6 target at normal impact incidences. To do so, a numerical case study driven by observations from impact experiments was conducted. More specifically, normal impact testing of an AlMg6 target hit with a projectile with a 45° half-angle was performed and, in addition to uniaxial material characterisation testing, delineated the projectile and target constitutive behaviours. 2. Material and main methodology This section presents the constitutive descriptions of the target and projectile, together with details on the projectile geometry and impact configuration. 2.1. Target description AlMg6 was considered in this work as the target material, with a constant thickness of 3.5 mm and unchanged planar dimensions, with height, H , and width, W , of 300 mm and 200 mm, respectively. The target was clamped at one of its short edges, in a cantilever arrangement, with the clamping region equal to 160 mm × 50 mm (more details on the arrangement are provided in Stergiou et al. (2021)). With respect to material properties, the target experienced work- and strain-rate hardening, as well as thermal softening. Quasi-static uniaxial tensile tests at ambient conditions suggested that the yield strength of the batch examined was 149 MPa, while the elastic modulus had a mean magnitude of 72 GPa. Additional uniaxial tensile testing was conducted at elevated rates of deformation and temperatures up to 150°C. An optimisation scheme was employed (Stergiou et al., 2021) to predict the most suitable flow-stress formulation and parameters for five Johnson-Cook (JC) and two Zerilli-Armstrong (ZA) formulations (Hallquist, projectile’s half -angle projectile ’s deceleration , ̇ plastic strain and plastic strain rate projectile’s density target’s quasi -static yield strength 1. Introduction