PSI - Issue 68

Hande Vural et al. / Procedia Structural Integrity 68 (2025) 573–580

577

Vural et al. / Procedia Structural Integrity 00 (2024) 000–000

5

Exterior zone

2

Transition zone

Contact zone

10

28.4

200

Hemispherical Bllunt

7.62 API

6.06

6.06

6.06

T4 T2-2 T2(6)2 T1-3 T3-1 T1-1-1-1

Fig. 2: Geometry of the projectiles and target configurations. Dimensions are given in mm.

The mesh structure of the FE model is shown in Figure 2. Target is divided into 3 di ff erent regions and meshed with the eight-node linear brick element (C3D8R) with reduced integration. The 10 mm diameter contact zone is surrounded by a transition zone with diameters of 10 mm and 12 mm. The contact and exterior zones are meshed with hex elements, while the transition zone is meshed with tetrahedral elements to reduce the number of elements in the thickness of the exterior zone. In the mesh study, the 7.62 API projectile is una ff ected by mesh changes, but hemispherical and blunt projectiles are mesh-sensitive. The finest mesh with an element size of 0.1 mm is used in the contact region and elements with a size of 0.2 mm are used in the arc edge. The exterior zone is meshed with elements of 5 mm. The interaction between the projectile and the target is defined using surface-to-surface contact, with normal behavior governed by a hard contact algorithm, and the tangential behavior assumed to be frictionless. General contact without friction is applied for multilayer surfaces, and the simulation time increment is set to 3e-10. 4. Results and Discussion This section presents numerical simulations evaluating the ballistic performance of monolithic and multilayer tar gets under di ff erent projectile types and velocities, comparing various damage models. In the experiment conducted by Iqbal et al. (2016), a 7.62 API bullet with an initial velocity of 823.62 m / s is utilized at an 8 mm thick Armox 500T target, and the residual velocity is measured as 334.28 m / s. The bar graph in Figure 3 illustrates the percent age di ff erences between this experimental residual velocity and the velocities predicted by each damage model. The OH model has the lowest error margin with only 7.56% deviation,provides the best prediction performance, whereas the Freudenthal and Le Roy models show the highest percentage di ff erences and demonstrate poor performance in terms of prediction residual velocity. The Ayada-m, Ayada, Ko-Huh, and JC models cluster within a 10-11% range, demonstrating moderate prediction accuracy. The CL model, while showing a higher percentage di ff erence of 16.13%, performed better than the Le Roy and Freudenthal models. Overall, the OH model aligns more closely with experi mental results than the commonly used JC model, indicating that di ff erent single-parameter damage models are also be used e ff ectively in ballistic impact studies. Di ff erent failure mechanisms can occur depending on the projectile nose shape. Figure 4 shows the failure mecha nisms observed in ballistic impact simulations using the Oh damage criterion at an initial velocity of 500 m / s, covering three di ff erent projectile types and six configurations. For the 7.62 API, it is observed that the main failure is hole en largement in all configurations, while hemispherical projectiles exhibit low fragmentation and petal forming as a failure mechanism. In the blunt projectile, large parts are apart from the target in all cases, indicating that the main mechanism is shear plugging. Depending on the failure mechanism, the gaps between the plates varied. For example, the largest gap is observed with blunt projectiles, while the largest geometrical deformation occurs with the hemi spherical projectiles. Both the gap between the plates and the geometric change are at the lowest level in the 7.62 API. When comparing configurations for di ff erent projectile types such as T2-2 and T1-1-1-1, the hemispherical projectile shows the highest ballistic resistance, while the 7.62 API have the lowest. Furthermore, the T2-2 configuration demon strates better ballistic resistance than the T1-1-1-1. This comparison highlights how di ff erent nose shapes and target configurations a ff ect ballistic response. Multi-layered targets generally provide better resistance, especially against hemispherical and blunt projectiles at 500 m / s initial velocity.