PSI - Issue 52

Huadong Xu et al. / Procedia Structural Integrity 52 (2024) 52–62 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

59

8

UHMWPE and aramid fabric targets are not penetrated, and largely transverse deflection are observed in the impact center area (Fig. 4 (a)-S1-3 and (b)S2-3). Witness plates are intact. The UHMWPE fabric target has 35 layers, of which 27 layers are penetrated by the projectile, and the remaining 8 layers are not penetrated. The remaining mass accounted for 22.86 % of the total mass. The Aramid fabric target has 56 layers, of which 47 layers are penetrated by the projectile, and the remaining 9 layers are not penetrated. The remaining mass accounted for 16.07 % of the total mass. All other targets are penetrated by the projectile, and show significantly impact damage on their witness plate compared to the UHMWPE and Aramid fabric target. Witness plates from the Quartz (Fig. 4 (c)), Basalt (Fig. 4 (d)), Nextel (Fig. 4 (e)), Al mesh (Fig. 4 (f)) and Carbon fiber fabric (Fig. 4 (g)) targets show a random pattern of damage, and this behaviour can be attributed to the non-isotropic fabric structure. While for Al plate target, circular damage pattern is perceptible on the witness plate (Fig. 4 (h)-S8-3). By far the largest damage is recorded by the witness plate of the Al plate target. Clearly identifiable are impact craters around a central region caused by fragments from projectile and target. Completely yarn breakage was observed at the hypervelocity impact vicinity in experimental and simulation results of fabric specimens. However, it is not clearly observed that primary yarns being pushed apart by projectiles frequently occurs at low impact. Under hypervelocity impact, the interaction time between the yarn and the projectile is very short, which limits the relative motion between the yarns, so that the extremely high yarn strength is fully utilized in debris shielding. The fragments from the fabric target are distributed radially on the witness plate, and the SEM (Scanning Electron Microscope) images of fiber fragments are shown in Fig. 5.

(a)

(b)

(c)

(d)

Fig. 5. Micromorphology of various fiber fragments. (a) Nextel fiber fragments. (b) Basalt fiber fragments. (c) Quartz fiber fragments. (d) Carbon fiber fragments. As shown in Fig. 5, fiber fragments contain fiber powder and short fibers. Among them, the length of Nextel, Basalt, and Carbon short fiber is about 20~100 μm ( Fig. 5(a), (b), and (d)), and length of Quartz fiber is small, with an average of about 20 μm, and most of the fiber debris is powder ( Fig. 5(c)). Further, it can be inferred that brittle fracture occurs during HVI from the fracture cross-section and appearance of the fiber fragments. Compared with the secondly fragments generated by the Al plate target, the fragments generated by the fabric target have smaller mass, lower kinetic energy, and lower penetration performance, which can further reduce the damage to the bulkhead.