Flat-nosed Projectile Research Articles

Static and dynamic loading of an ovaloid toroidal tank

In this study, two problems of static and dynamic loading for an ovaloid toroidal tank are considered. In the first problem, a linear elastic three-dimensional finite element analysis is carried out to determine the stress concentration in a pressurized ovaloid toroidal tank with a nozzle. For validation, comparison is made with previous results for a cylindrical shell with a nozzle. An analysis is carried out to indicate the influence of the nozzle location on the stress concentration. Results are provided for three ovaloid toroidal tanks, to indicate the variation of the stress concentration with nozzle geometry. In the second problem, a non-linear elastic–plastic shell-theory finite element analysis is carried out to determine the displacements arising in an ovaloid toroidal tank due to impact by a flat-nosed projectile. For validation, comparison is made with previous results for a spherical shell impacted by a projectile. Results are provided for three ovaloid toroidal tanks, impacted at the extrados or the crown, and these results are compared with results for equivalent shells of related geometry. Conclusions are drawn, noting characteristics of ovaloid toroidal tanks relevant to their design.

The influence of a steel rear barrier on the detonation response of a steel covered explosive struck by a steel projectile

Abstract Experiments by Weickert showed that the critical impact velocity of a shaped charge jet, required to cause detonation of a steel/explosive/steel laminate, reduced when the explosive thickness reduced. This paper examines the cause of this change using hydrocode simulations with and without a temperature based burn model. The simulations show that the change in critical impact velocity is caused by the reflected shock from the rear plate exceeding the shock at the cover plate. At this point the site of the detonation moves from the cover plate to the rear plate. Further reduction in explosive thickness causes further reduction in critical impact velocity due to the reduced dissipation of the shock reaching the back plate. The change in critical velocity for hemispherical-nosed projectiles is predicted to be not as sharply defined as for flat-nosed projectiles. This is due to a later, third stage reflection from the bulge of the advancing cover plate.

Ballistic limit for oblique impact of thin sandwich panels and spaced plates

Ballistic perforations of monolithic steel sheets, two-layered sheets and lightweight sandwich panels were investigated both experimentally and numerically. The experiments were performed using a short cylindrical projectile with either a flat or hemispherical nose that struck the target plate at an angle of obliquity. A total of 170 tests were performed at angles of obliquity 0–45°. The results suggest that during perforation by a flat-nosed projectile, layered plates cause more energy loss than monolithic plates of the same material and total thickness. There was no significant difference in the measured ballistic limit speed between monolithic plates and layered plates during oblique impact perforation by a hemispherical-nosed projectile. To develop understanding of the process of fracture development and perforation of a thin stainless-steel sheet resulting from oblique impact by a hard, flat-nosed projectile, numerical simulations by ABAQUS/Explicit finite element code were compared against the experimental fracture patterns, residual velocities and ballistic limits of perforated plates. Effects of projectile length-to-diameter ratio and spacing between layered plates struck by flat-nosed projectiles were investigated. For projectiles of equal mass, a longer projectile (larger ratio of length to diameter, L/ D>2) results in a drastic decrease in the ballistic limit speed for a double-layered plate. For thin, layered plates, the ballistic limit speed is affected significantly by the spacing between layers.

Penetration resistance of aluminium foam

The resistance of aluminium foam against projectile penetration has been studied experimentally and analytically and the results are presented in this paper. The penetration depth of a rigid, flat-nosed projectile into an aluminium foam target was measured at various impact velocities between 20 m/s and 120 m/s. An analytical model based on crushing stress shock enhancement theory is presented to offer estimation for the penetration depth into aluminium foam target by such a projectile.

Dynamic shear plugging of beams and plates with an advancing crack

The perforation response of a thin or intermediately thick beam/plate struck by a rigid, heavy, flat-nosed projectile traveling at a high velocity is studied analytically. Based on a newly developed expression relating indentation depth to crack length, a shear-plugging model including two stages: indentation and crack growth, is proposed. In this model, shear resistance in the ligament decreases as the cracks propagate through the target thickness. The closed-form solutions for residual velocities, plastic energy, shear zone width, crack propagation speeds, and temperature rise are derived. A coupled shear–tension solution that takes into account global deformation of the plate is also developed. The coupled solution improves prediction for the case with the initial impact velocity near the ballistic limit. Comparisons with experimental results presented in the open literature are made showing rather good correlation, which validates the accuracy of the present solution.

Dynamics of a Projectile Penetrating Sand. Part II

Additional data are reported that confirm a theory presented in a previous paper for the penetration of a stable flat-nosed projectile in sand. The negative acceleration of the projectile can be expressed by the relations: −dv/dt=αv2, v0>v>vc; −dv/dt=βv2+γ, vc>v>0 where the coefficients α, β, γ are positive constants and v0 is the striking velocity. In the case where air is removed from the sand and the sand is loaded transverse to the trajectory by one atmosphere pressure, the coefficients α and β are characteristic of inelastic and elastic impact, respectively, where the flow process is regarded as Newtonian. An additional experiment has been performed where quartz powder produced by impact is plotted as a function of initial projectile energy. Although the powder production curve can be represented roughly as a straight line through the origin, there are small discontinuities in slope corresponding to the critical velocity v=vc. The velocity of sound in sand has been measured under the conditions of the experiments. Loading increases the velocity of sound markedly but has little effect on the critical velocity vc.