Projectile

About: Projectile is a research topic. Over the lifetime, 13047 publications have been published within this topic receiving 115563 citations.

The African Origin of Complex Projectile Technology: An Analysis Using Tip Cross-Sectional Area and Perimeter

Abstract: Despite a body of literature focusing on the functionality of modern and stylistically distinct projectile points, comparatively little attention has been paid to quantifying the functionality of the early stages of projectile use. Previous work identified a simple ballistics measure, the Tip Cross-Sectional Area, as a way of determining if a given class of stone points could have served as effective projectile armatures. Here we use this in combination with an alternate measure, the Tip Cross-Sectional Perimeter, a more accurate proxy of the force needed to penetrate a target to a lethal depth. The current study discusses this measure and uses it to analyze a collection of measurements from African Middle Stone Age pointed stone artifacts. Several point types that were rejected in previous studies are statistically indistinguishable from ethnographic projectile points using this new measure. The ramifications of this finding for a Middle Stone Age origin of complex projectile technology is discussed.

Foreign object damage in a thermal barrier system: Mechanisms and simulations

Abstract: Experimental studies have been performed of foreign object damage (FOD) imparted to a thermal barrier system under conditions representative of those found in a turbine engine. The sub-surface damage has been characterized by using the focused ion beam (FIB) imaging system. The characterization reveals changes in the thermal barrier coating (TBC), caused by particle impact, that confirm and elaborate previous observations of FOD. These features include a permanent impression, a zone of densification, shear bands penetrating from the impact site to the interface with the bond coat, and delamination cracks extending away from the impact in the TBC adjacent to the interface. The dimensions of these features have been reported. A simulation procedure has been devised and implemented. The simulations have been performed in conjunction with a new non-dimensional analysis that allows the impact and material variables to be grouped into the smallest possible parameter set needed to characterize the stresses and projectile velocities, as well as the impression and densification zone dimensions. This parameterization provides explicit results for the stresses and displacements that arise as the projectile characteristics and material properties are varied over a range applicable to FOD in gas turbines. A scaling relation has been derived from the stress field and the penetration that relates the length of the interface delamination to the impact and material variables. A comparison of the simulations with the measurements indicates that the unknown impact velocity of the projectile can be ascertained from the penetration depth if the yield strength is known and vice versa. With this information, the scaling relation for the size of the interface delamination indicates consistency with the measured cracks. The implication is that delamination can be suppressed by lowering the high temperature hardness of the TBC and by increasing its toughness.

Finite element simulation of ceramic/composite armor under ballistic impact

Abstract: In this paper, based on LS-Dyna code, a new finite element (FE) simulation of the ballistic perforation of the ceramic/composite targets, which impacted by cylindrical tungsten projectiles, has been presented. Research on this method has been conducted by a few research groups in recent years. The ceramic material, which is the front plate, has been made of Alumina 99.5% and composite back-up plate composed of Twaron fibers. The 2-dimensional (2D), axi-symmetric, dynamic-explicit, Lagrangian model has been considered in this simulation. The Johnson–Cook, Johnson–Holmquist and Composite-Damage materials behaviors have been used for projectile, ceramic and composite materials respectively. The brittle fracture and fragmentation of ceramic conoid, the failure criteria based on fracture of fibers or matrixes of composite materials and erosion or flattening of projectile during perforation have been considered. The residual velocity and perforation time has been obtained and compared with the available analytical models. The results show that when the ceramic is impacted by a projectile, a fragmented ceramic conoid breaks from ceramic tile and the semi-angle of ceramic conoid with increasing initial velocity decreases. Furthermore, the dishing of composite layers at high impact velocities and the delamination of layers near the ballistic limit velocity decrease.