David J. Chapman

Dynamic compaction of porous silica powder

The dynamic compaction characteristics of a porous silicon dioxide (SiO2) powder are reported. The initial specific volumes of the samples were either V00=1.30, 4.0, or 10.0cm3∕g whereas the silicon dioxide has a matrix specific volume of V0=0.455cm3∕g. The impact velocity ranges from 0.25to1.0km∕s and the shock incident pressure on the silica ranges from 0.77to2.25GPa. The shock velocity–particle velocity exhibited a linear relationship within this range. Although these tests represent the low end of dynamic compaction, the dynamic tests compare favorably to extrapolated data available in the open literature. Theoretical pressure–particle velocity and shock velocity–particle velocity curves were generated using a P-α compaction curve. The P-α compaction curve accurately represented the pressure–particle velocity and shock velocity–particle velocity Hugoniot curves for the low specific volume powder, specifically V00=1.30cm3∕g. However, the P-α compaction curve did not accurately represent the pressure–pa...

THE DYNAMIC COMPACTION OF SAND AND RELATED POROUS SYSTEMS

Porous and granular materials are widely found in a number of environments. One of the most important groups both geographically and in the construction industry are the sands. A review of the response of sand (42% porous) over a wide range of strain rates is presented. Factors such as water content and density variation are addressed. In addition a very low‐density silica dust (95% porous) is also discussed in relation to its contrasting behaviour.

THE RESPONSE OF DYNEEMA TO SHOCK‐LOADING

Dyneema is a registered trademark of a self‐reinforced polyethylene (manufactured by DSM) which is showing great promise as a replacement for brittle‐fibre‐reinforced epoxies in various dynamic applications. As part of an investigation of its high‐rate mechanical properties, we have measured the response of Dyneema under the condition of uniaxial strain during shock‐loading. Data on the principal‐Hugoniot curve was obtained using in‐material manganin stress gauges to measure both longitudinal stress and shock‐wave velocity. Off‐Hugoniot data was generated using a plate‐impact reverberation technique, where a Dyneema sample was sandwiched between two higher impedance copper anvils. Manganin stress gauges mounted at the interface between the Dyneema sample and copper anvils monitored the ring‐up of stress in the specimen. Finally, the release curve from a given principal‐Hugoniot state was measured using a reverse ballistic impact technique where free‐surface velocity was measured using VISAR.

Hugoniot and spall strength measurements of porous aluminum

Plate impact experiments were performed on 14% porous aluminum samples to measure the principal Hugoniot and the spall strength. The principal Hugoniot was measured by performing multiple experiments at a range of flyer velocities, from 0.25–0.89 km/s, leading to incident shock pressures in the target from 0.6–4.8 GPa. The shock compaction data were compared to a theoretical Hugoniot determined from a Mie–Gruneisen equation of state and was found to agree very well over the stress range investigated. Spall strength measurements were performed on the 14% porous aluminum samples at impactor velocities of 0.224, 0.230, and 0.306 km/s. Spall strengths of 78±8, 55±28, and 36±7u2002MPa, respectively, were measured for the porous Al samples. This is thought to be the first measurement of spall strength in a shock compacted porous ductile material.

The effect of particle size on the shock compaction of a quasi-mono-disperse brittle granular material

Several continuum models aim to represent the shock compaction of brittle granular materials but their success is limited by their insensitivity to the effects of meso-scopic features. This investigation is part of early attempts to quantify the effects of particle size on the macro shock response of a granular material. Plate impact experiments were conducted on beds of soda-lime glass microspheres. Three different quasimono-disperse particle size distributions were subjected to shock pressures between 0.6 - 4.5 GPa. There is an obvious difference between the compaction behaviour of 63 μm particles compared to beds of 200 and 500 μm particles. A precursor wave is present at low stresses that potentially signifies bulk material strength; the precursor magnitude decreases with increasing particle size.

Shock-precursor waves in brittle granular materials

Shock compaction studies of sand, and other brittle granular materials, have produced wave profiles that show an unsteady precursor-wave followed by a steady shock-wave. Two theories exist regarding the meso-mechanical deformation that occurs within this precursor wave: inter-particle rearrangement and particle fracture. Plate impact experiments were conducted on beds of quasi-mono-disperse soda-lime glass microspheres. The thickness of the granular bed was varied to measure evolution of the precursor waves. Granular beds comprising smaller particles produce higher magnitude precursor waves which indicates a higher bulk material strength. This theory of increasing strength with decreasing scale agrees with other studies. The precursor waves within beds of 63 μm microspheres appear to reach a steady state within the run distance of the beds used in this investigation but thicker beds of 200 and 500 μm particles are potentially required to observe a steady state precursor wave.

Hugoniot Properties of Dry Yorkshire Sandstone up to 8 GPA

A series of plate impact experiments has been performed to assess the dynamic behaviour of dry Yorkshire sandstone up to 8 GPa. Standard manganin gauges were inserted between samples in order to determine the principal Hugoniot curve. A VISAR system was used to measure the free surface velocity of the target. This work is in part of a research programme to understand the survivability of microbial life under impact and the creation of new habitats for microbial life as a function of shock processing of sandstone.

Dynamic Compaction Modeling of Porous Silica Powder

A computational analysis of the dynamic compaction of porous silica is presented and compared with experimental measurements. The experiments were conducted at Cambridge University’s one‐dimensional flyer plate facility. The experiments shock loaded samples of silica dust of various initial porous densities up to a pressure of 2.25 GPa. The computational simulations utilized a linear Us‐Up Hugoniot. The compaction events were modeled with CTH, a 3D Eulerian hydrocode developed at Sandia National Laboratory. Simulated pressures at two test locations are presented and compared with measurements.

THE RESPONSE OF DRY LIMESTONE TO SHOCK‐LOADING

The shock response of geological materials is of interest to many industries, in particular oil and gas exploration. The porous inhomogeneous composition of geological materials complicates characterisation under dynamic loading. The behaviour of dry limestone has been investigated under the condition of uniaxial strain using a plate impact facility. Manganin gauges were used to measure both longitudinal and lateral stresses within the limestone. The Hugoniot and shear data obtained are compared with that available in the open literature.

Experimental Hugoniot Data of Porous Silica

The response of a commercially available silica powder at low density to shock loading has been investigated. Hugoniot data were obtained for samples from two initial densities. The shock velocity particle velocity dependence was found to be linear for both densities. The data is modelled using a P‐α model and reported in a companion paper.