Dynamic behavior of an aggregate material at simultaneous high pressure and strain rate: SHPB triaxial tests

Abstract

International audienceLow velocity impacts on energetic materials induce plastic deformations and sliding friction which can lead to ignition. If some ignition criteria have been proposed, the remaining difficulty is to characterize the mechanical behavior of the material when submitted to the corresponding solicitations (high pressure and high strain rate). Thus, a technique based on the Split Hopkinson Pressure Bars system is proposed to carry out a triaxial compression test. A cylindrical specimen is placed into a confining ring and is compressed by the system of bars. The ring prevents the radial extension of the specimen and creates a lateral confining pressure. The material and dimensions chosen for the ring maintain a constant radial pressure during the test. Some tests were carried out on an inert aggregate material and proved the validity of this experimental device. The experimental data processing shows the influence of both the pressure and the strain rate. The shear stresses, which contribute to thermal dissipation and then to the ignition threshold, increase according to the pressure

Effects of imperfect experimental conditions on stress waves in SHPB experiments

“…The SHPB has been widely used to investigate the dynamic mechanical properties of materials under uniaxial compression [5,6,[8][9][10][11]. The SHPB apparatus comprises three elastic bars that are the striker, the incident bar, and the transmitted bar.…”

A friction test between steel and a brittle material at high contact pressures and high sliding velocities

“…Comparisons between the numerical results obtained with and without the spring-cap contact on figures [11][12][13] show that spring stretching has not an immediate influence on the mechanical response. At the beginning of the test, the compression of the sample is actually due to the inertia of the rod and the spring.…”

“…It is a fine powder mixed with a binder which has been compacted. Its mechanical behaviour has been previously studied [11]. Its elastic properties are a 0.4 Poisson's ratio and a 3 GPa Young's modulus.…”

“…Quasi-oedometric tests consist in confining a cylindrical sample in a rigid ring [11][12][13] and applying high stresses on brittle materials without reaching their shear resistance criterions. Indeed, under increasing magnitudes of hydrostatic pressures, materials with a Drucker-Prager's threshold can reach higher octahedral scissions.…”

Simulations of Deformation Processes in Energetic Materials

“…In other tests more sophisticated experimental methods and highly instrumented diagnostics allow the detailed mechanical behavior to be inferred from the data; for example, the split Hopkinson pressure bar. In many cases simulations are required to aid in the interpretation of the data; specific examples for the split Hopkinson pressure bar, Steven impact, and LANL impact tests can be found in (Bailly et al, 2011;Gruau et al, 2009;Scammon et al, 1998). The ballistic impact chamber is a specific drop-weight impact test designed to impose a shear deformation in a cylindrical sample of explosive (Coffey, 1995).…”