Determining the degree of pulse absorption of air blast wave by spaced material systems

The paper presents the results of a study to determine the degree of attenuation of a detonation wave pulse generated by a spherical ceresin-phlegmatized hexogen charge, by spaced material systems. The systems were mounted on a ballistic pendulum and the amount of energy absorbed was determined based on the change in pendulum swing. The spaced panels with absorbing elements, simulated the flat bottom of a vehicle exposed to a single blast.

Experiments in the Principia

Newton carried out four groundbreaking experiments in conjunction with the Principia and proposed a fifth. This chapter reviews his reasons for doing them, their design, and what they achieved. The four include a two-pendulum experiment early in 1685 to establish that the action of gravitational forces on a body is always proportional to its mass and hence that all bodies at any point respond to a gravitational force in the same way. In that same year he conducted a ballistic pendulum experiment to establish that this third law of motion holds for impact of spheres of a wide range of elastic responses, in the process identifying what became known as the coefficient of restitution. He carried out two sets of experiments measuring fluid resistance forces on spheres, the less than successful first relying on pendulum decay and then, for the second edition, vertical-fall. All five experiments were designed to “put the question to nature” in the sense that the three laws of motion enable their results to yield theory-mediated answers to theretofore open questions about forces—and thus parallel the answers to questions about celestial forces drawn from planetary motions that form the core of the Principia.

Assessing safety conditions in underground excavations after a methane-air mixture explosion

A technique for evaluation of shock wave impulse after a methane-air mixture explosion is elaborated. The numerical model developed in previous studies has been verified in the laboratory by using laser initiation of explosives and measuring the pressure impulses of explosion products on a ballistic pendulum. To evaluate the mechanical impulse the functional correlations between its magnitude, the swing angle, and the pendulum characteristics have been derived analytically. The reliability of experimental results is ensured by calibrating the sensor that measures the pendulum swing angle and estimating the impulse measurement errors caused by specifics of angle measurements by a digital voltmeter, pendulum axis friction, and the pauses between measurements. Testing the developed technique to evaluate the shock wave impact showed satisfactory consistency of experimental and theoretical results with the momentum deviation below 9%, which confirms model applicability and correct reproducibility of the shock wave propagation process.

The response of quadrangular plates to blast load resulting from the detonation of encased buried charges

In real-life situation, especially in the numerous regions where conflicts exist, improvised explosive devices can be made of varying explosives encased in different containers detonated under varying conditions. This article reports on a series of experiments that was carried out to investigate the response of quadrangular plates to buried encased charges with a view to simulate the detonation of landmines buried in sand and compared with different loading conditions. Four loading scenarios, namely, bare and encased charges detonated in air and bare and encased charges buried under sand, were investigated. The results were evaluated and compared to the data obtained from bare charges detonated in air in terms of plate deformation and impulse imparted onto the target plate. A vertical ballistic pendulum was used to measure the impulse imparted onto the target plates by the different charges. The results showed that the presence of the steel casing in buried charge tests caused more damage to the test plate. An increase in the midpoint deflection of the test plate was observed despite a slightly reduced impulse imparted onto the plate. Larger impulse was imparted onto the target plate by buried bare charges compared to bare charges detonated in air. Midpoint deflection and impulse decreased with an increasing stand-off distance for all the different loading scenarios.