PSI - Issue 37

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

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(3)

and solving for results in the following expression for the target resistance = 1 ( /ℎ ) 1− 2 .

(4)

Fig. 5: Effect of normalised nose length on target resistance. In orange, the asymptote representing the limiting value of the resistance at blunt impact.

The normalised target resistance to penetration as a function of the normalised projectile ’s nose length is shown in Fig. 5, with the black dashed line presenting the prediction of Eq. (4). The data points in each case were derived by estimating the local-work term from subtracting the target ’s internal energy (excluding the local-erosion term) from the projectile ’s critical kinetic energy. Clearly, the predicting capability of Eq. (4) is satisfactory, capturing both the general trend, and comparing well with the observed results. Fig. 5 illustrates the deterioration of the target ’s local resistance with /ℎ . At the lowest value of the half-angle (largest /ℎ ), the local target resistance is the fourfold of the quasi-static yield strength because of the high value of resistance path. Evidently, projectiles with higher half-angles caused a decrease in the target resistance, that deteriorates rapidly with /ℎ , reaching the limit of ≈ as the half-angle approached 90°. At that point, complete blunt impact occurred and failure by stretching dominated. In their analysis, Rosenberg and Dekel (2020) suggested that a value of = 8.52 should be used for the target resistance for an axisymmetric projectile with an equivalent shank ’s cross-sectional area and target thickness. This value is considerably higher than the one observed herein for non-axisymmetric projectiles, suggesting that the capability of the target to resist non-axisymmetric projectiles is considerably lower than that for the equivalent axisymmetric case. This discrepancy may have resulted from the fact that for the non-axisymmetric projectile, the plane-stress state was predominant due to the high projectile width, while the plane-strain state with higher projectile ’s confinement was observed for the axisymmetric projectile case, resulting in higher target resistance.