PSI - Issue 72

Toeri Fathuddin Yusuf et al. / Procedia Structural Integrity 72 (2025) 436–444

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to surrender and commit violence and even murder. Firearms are the most commonly used weapon in pirate attacks, with the highest success rate for attacks on docked vessels (Forster et al., 2014). Southeast Asia and Somalia have seen the highest number of ship attacks in the last decade (Beckman et al., 2014). Ship hijacking not only jeopardizes the safety of the crew but also causes enormous economic losses due to loss of cargo, ransom fees, and disruption to international trade routes. The reinforcement of the protective plates on the ship's side walls is designed to increase resistance to attack, especially in vulnerable areas, such as the engine room, command bridge, and cargo hold. Through this approach, the ship gains additional physical protection. It is capable of withstanding the initial attack of armed piracy, allowing time for the crew to respond and take other mitigation measures. Therefore, further research is needed to develop a ship plate structure that is not only strong but also lightweight and cost-effective. The application of this plate structure is expected to improve ship safety in high-risk shipping lanes (Suryanto et al., 2023;2024; Rahman et al., 2024a; Saputra et al., 2024; Ahzhan et al., 2024). 2. Review on the ballistic phenomenon A 2D numerical simulation was conducted to investigate the penetration of a rigid rod into a semi-infinite metal target (Rosenborg et al., 2009). It was found that when the impact velocity ( 0 ) is less than the threshold value ( ), the rod decelerates continuously during the penetration phase. The deceleration occurs until it reaches a threshold that indicates the beginning of cavitation in the penetration channel. When this deceleration occurs, the result is independent of the impact velocity if it is below the threshold value. Using an appropriate formula, it is possible to model the simple penetration of a rigid rod into a semi-infinite metal target, both for low velocities ( 0 < ) and high velocities ( 0 > ) (Rahman et al., 2024b; Alwan et al., 2022). In the research conducted by Chen et al. (2002), there are three penetration mechanisms: rigid penetration, semi hydrodynamic penetration, and hydrodynamic penetration. Some studies show that the projectile's mass loss and kinetic energycause changes in the geometry and shape of the projectile nose. This mass loss occurs in the outer surface layer of the projectile. For example, the shape will change to blunt after impact in the ogive-nose projectile, and the projectile's mass is reduced by more than 7% (Frew et al., 1998). In addition, the material hardness of the target plate significantly affects the projectile during impact. A subsequent study by Rosenborg et al. (2010) used a numerical method with the projectile shape unchanged during the impact process. To simplify the analysis, the material in the target plate used the von Mises elastoplastic model without considering strain rate or strain hardening. This simplification derives the relationship between the relevant ballistic parameters: the projectile's residual velocity and the target plate's hardness. 2.1. Determining the effective stress In the study presented by Recht et al. (1963), Eq. 1 is known to determine the ballistic limit velocity ( ), with initial velocity ( 0 ) and residual velocity ( ). =( 0 2 − 2 ) 0.5 (1) Then, in the article by Rosenberg et al. (2009), Eq. 2 is derived from Eq.1 to obtain the target effect resistance value ( ). = . . 2 2 (2) where is the density of the projectile, is the effective length of the projectile, and is the thickness of the target plate. Based on Eq. 2, the target plate affects projectile perforation. Based on Eqs. 1 and 2, it can be seen that there is a change in the ballistic limit velocity for wider target plates. The ballistic limit velocity value for coated target plates is lower than that of monolithic targets (Dey et al., 2007). This is due to the shear and tensile stresses in the coated target plate that cannot be transmitted directly, thus reducing its