Young’s Modulus Calculus Using Split Hopkinson Bar Tests on Long and Thin Material Samples

Young’s modulus is a key parameter of materials. The method of its calculation in the current paper is concerned with the mismatch of the mechanical impedance at the bar/specimen interface for a compression SHPB (split Hopkinson pressure bar) test. By using long and thin specimens, the signal recorded in the transmission bar presents itself as a multistep signal. The ratio between the heights of two successive steps represents the experimental data that are considered in the formula of the elastic modulus this article is devoted to. The oscillatory nature of the real signals on the horizontal or quasi-horizontal segments prevents a precise determination of the two successive step heights ratio. A fine tuning of this value is made based on the characteristic time necessary for the signal to rise from one level to the next one. The FEM (Finite Element Method) simulations are also used in calculation of the Poisson coefficient of the tested complex concentrated alloy

A HiLo interior ballistic model based on the hypothesis of gases adiabatic transformation in the high pressure chamber

Weapons built on high-low pressure (HiLo) principle involve the existence of two chambers between which a gas flow occurs. The usual approach in the mathematical models developed for such systems is to consider that the gas flow is accompanied by an isothermal transformation of gas in the high pressure chamber. The present paper deals with the development of a lumped interior ballistic model built on more realistic assumptions like an adiabatic transformation of the gases in the high pressure chamber, an isentropic flow of real gases through the nozzles, a variable burning surface of the propellant grains and the occurrence of heat losses at the level of vent holes lateral surfaces. The experimental results obtained with a modified closed vessel were used in order to validate the proposed model. The pressure time variations in both chambers were accurately predicted by the proposed lumped model. The lumped model application on a 40 mm grenade launcher gives results consistent to the experimental measurements regarding the grenade muzzle velocity

Ballistic and thermal characterisation of greener composite solid propellants based on phase stabilized ammonium nitrate

Several representatives of a new class of ''greener'' propellants, comprising polyurethanes (based on recycled PET) as the binder, phase stabilized ammonium nitrate (PSAN) as the eco-friendly oxidizer, and triethylene glycol dinitrate (TEGDN) as the energetic plasticizer, together with aluminium-magnesium alloy as fuel and iron oxide powder (α-Fe2O3) as the catalyst, were prepared and investigated through specific analytical tools. Besides morphological and compositional investigations, the thermal behaviour and ballistic properties of the propellants were determined, and compared to those of consecrated propellants compositions, based on ammonium perchlorate. The calorimetric tests were used to measure the heat of combustion and specific volume. Impact and friction sensitivities were also measured. The ballistic tests carried out in closed bomb and the original data processing approach used allowed, in addition to the propellant force and covolume, the identification of a critical parameter such as the power index from Vieille's law of the burning rate

Experimental and Numerical Study on Perforated Plate Mitigation Capacity to Near-Field Blasts

Based on the analysis of existing collective shockwave protection methods worldwide, this paper addresses the mitigation of shock waves by means of passive methods, namely the use of perforated plates. Employing specialized software for numerical analysis, such as ANSYS-AUTODYN 2022R1®, the interaction of shock waves with a protection structure has been studied. By using this cost-free approach, several configurations with different opening ratios were investigated, pointing out the peculiarities of the real phenomenon. The FEM-based numerical model was calibrated by employing live explosive tests. The experimental assessments were performed for two configurations, with and without a perforated plate. The numerical results were expressed in terms of force acting on an armor plate placed behind a perforated plate at a relevant distance for ballistic protection in engineering applications. By investigating the force/impulse acting on a witness plate instead of the pressure measured at a single point, a realistic scenario can be considered. For the total impulse attenuation factor, the numerical results suggest a power law dependence, with the opening ratio as a variable

Impact Behavior of the Ballistic Targets Package Composed of Dyneema Polymer and High Entropy Alloy Structures

Ballistic targets are multi-material assemblies that can be made of various materials, such as metal alloys, ceramics, and polymers. Their role is to provide collective or individual ballistic protection against high-speed dynamic penetrators or kinetic fragments. The paper presents the impact behavior with incendiary perforating bullets having 7.62 mm of ballistic packages made of combinations between Dyneema ultra-high-molecular-weight polyethylene and high entropy alloy from alloying system AlCoCrFeNi, by analyzing the dynamic phenomena (deformation, perforation) that take place at high speeds. The geometry evolution of the physical model subjected to numerical simulation allows a very good control over the discretization network and also allows the export for modeling to nonlinear transient phenomena. The results obtained by numerical simulation showed that the analyzed ballistic package does not allow sufficient protection for values of impact velocities over 500 m/sec