High-velocity impact behavior of sandwich structures with AL faces and foam cores—Experimental and numerical study

In this research, the effect of layering of the foam core of sandwich structures with aluminum face-sheets (AL-1050) and also arrangements of these layers on the ballistic resistance of the structures under high-velocity impact were investigated experimentally and numerically. Three single-layer core sandwich structures and four sandwich structures with four-layer core were considered with a total fixed volume (90 ⁎ 90 ⁎ 63 mm3). These structures were impacted by a hemispherical nose cylindrical steel projectile of 20 mm length and 8 mm diameter. The impact velocity range was chosen from 188.7 to 322.6 m/s. The results of this study revealed that, considering constant core mass and total thickness, the core layering increases the ballistic limit velocity of the sandwich structures, so that the ballistic limit velocity of the sandwich structures with four-layer core, with different arrangements of layers, compared to the single-layer core structure is 5 to 8 percent higher, on average. Also, experimental and numerical results are in good agreement. In this research, the effect of parameters such as the sandwich structure core, the thickness of the face-sheets, the projectile nose geometry, the projectile diameter and mass on the ballistic limit velocity were investigated. The study showed that the removal of the core from the sandwich structure led to a 32% reduction in ballistic limit velocity. Increasing the thickness of the back face-sheet (with the constant total thickness of the two face-sheets) increases the ballistic limit velocity by more than 6%. Compared to flat nose projectile, the ballistic limit velocity of a hemispherical nose and conical nose projectiles are respectively 9.5 and 15.6% less. Considering a constant projectile mass, with an increase of 12.5 and 25% in its diameter, the ballistic limit velocity was increased by 6.5 and 14.4%, respectively, and by decreasing the diameter by 5 and 10%, the ballistic limit velocity dropped 7.9% and 13.5%, respectively. Assuming a fixed initial kinetic energy, the increase in the mass of the projectile also reduced the ballistic limit velocity, so that by increasing the 14 and 46.1% of the projectile mass, the ballistic limit velocity was reduced by 8.5 and 18.3%, respectively.