Justin Huneault

Phase velocity enhancement of linear explosive shock tubes

Strong, high-density shocks in a gas can be generated by end-initiating a hollow cylinder of explosive surrounding a pressurized thin-walled tube. Implosion of the tube results in a pinch that travels at the detonation velocity of the explosive, thereby driving a strong shock into the gas ahead of it. In the present study, the pinch velocity was increased beyond the detonation velocity of known explosives by dragging an oblique detonation wave along the surface of the tube. The gas shock and detonation trajectories were measured for a variety of phase velocities and tube fill pressures. Strong shocks with an average velocity of 13 km/s were observed for fill pressures as high as 6.9 MPa in helium while transient velocities as high as 19 km/s were observed. Shock trajectory performance degraded strongly with increasing phase velocity and for a velocity of 16 km/s the gas shock barely advanced ahead of the detonation.

Development of an accelerating piston implosion-driven launcher

The ability to soft-launch projectiles to velocities exceeding 10 km/s is of interest for a number of scientific fields, including orbital debris impact testing and equation of state research. Current soft-launch technologies have reached a performance plateau below this operating range. In the implosion-driven launcher (ILD) concept, explosives are used to dynamically compress a light driver gas to significantly higher pressures and temperatures than the propellant of conventional light-gas guns. The propellant of the IDL is compressed through the linear implosion of a pressurized tube. The imploding tube behaves like a piston which travels into the light gas at the explosive detonation velocity, thus forming an increasingly long column of shock-compressed gas which can be used to propel a projectile. The McGill designed IDL has demonstrated the ability to launch a 0.1-g projectile to 9.1 km/s. This work will focus on the implementation of a novel launch cycle in which the explosively driven piston is accelerated in order to gradually increase driver gas compression, thus maintaining a relatively constant projectile driving pressure. The theoretical potential of the concept as well as the experimental development of an accelerating piston driver will be examined.

Spall strength measurements in EPON 828 epoxy and an epoxy/carbon nanotube composite

Polymer nanocomposites are seeing more frequent use in armor applications. The role of the microstructure on the performance of these materials under dynamic tensile loading is of particular interest. In the present study, plate impact experiments were conducted in order to observe the dynamic response of a neat epoxy (EPON 828) and an epoxy/carbon nanotube composite. The objective was to examine the effect of nano-scale particle inclusions on the spall strength of the composite. The material response was resolved with the combined use of shock pins and a multi-channel photonic Doppler velocimeter. The addition of raw carbon nanotubes (CNT) to epoxy resulted in a composite material with lower spall strengths compared to strengths measured for neat epoxy at elevated shock stresses. Tensile strain rate was found to have the greatest effect on spall strength. Recovered composite fragments were imaged with a scanning electron microscope. Instances of nanotube pull-out were identified on internal fracture surfaces. The low spall strengths of the epoxy/CNT composite were attributed to an increase in the density of potential nucleation sites for spallation caused by presence of the nanotubes in the matrix.Polymer nanocomposites are seeing more frequent use in armor applications. The role of the microstructure on the performance of these materials under dynamic tensile loading is of particular interest. In the present study, plate impact experiments were conducted in order to observe the dynamic response of a neat epoxy (EPON 828) and an epoxy/carbon nanotube composite. The objective was to examine the effect of nano-scale particle inclusions on the spall strength of the composite. The material response was resolved with the combined use of shock pins and a multi-channel photonic Doppler velocimeter. The addition of raw carbon nanotubes (CNT) to epoxy resulted in a composite material with lower spall strengths compared to strengths measured for neat epoxy at elevated shock stresses. Tensile strain rate was found to have the greatest effect on spall strength. Recovered composite fragments were imaged with a scanning electron microscope. Instances of nanotube pull-out were identified on internal fracture surf...

Dynamic Tensile Strength of Silicone Oils

The spall strength of polydimethylsiloxane silicone oils has been studied using the planar impact of thin flyers to generate large transient negative pressures near the free surface of target samples. The liquids were contained within sealed capsules in which a 4-µm-thick aluminized Mylar diaphragm formed a free surface at the back of the sample. The liquid targets were impacted by PMMA flyers at velocities ranging from 130 to 700 m/s using a 64-mm-bore gas-gun, thus allowing for large variations in the strain rate and incident shock pressure. The peak tension in the liquid was determined by monitoring the free surface velocity using a photonic Doppler velocimetry (PDV) system. The paper focuses on the study of a system of silicone oils having vastly different viscosities (5 cSt to 1000 cSt), but otherwise similar liquid properties. The effect of viscosity on spall strength is compared to previously published data and models.The spall strength of polydimethylsiloxane silicone oils has been studied using the planar impact of thin flyers to generate large transient negative pressures near the free surface of target samples. The liquids were contained within sealed capsules in which a 4-µm-thick aluminized Mylar diaphragm formed a free surface at the back of the sample. The liquid targets were impacted by PMMA flyers at velocities ranging from 130 to 700 m/s using a 64-mm-bore gas-gun, thus allowing for large variations in the strain rate and incident shock pressure. The peak tension in the liquid was determined by monitoring the free surface velocity using a photonic Doppler velocimetry (PDV) system. The paper focuses on the study of a system of silicone oils having vastly different viscosities (5 cSt to 1000 cSt), but otherwise similar liquid properties. The effect of viscosity on spall strength is compared to previously published data and models.

Down-bore two-laser heterodyne velocimetry of an implosion-driven hypervelocity launcher

The implosion-driven launcher uses explosives to shock-compress helium, driving well-characterized projectiles to velocities exceeding 10 km/s. The masses of projectiles range between 0.1 – 15 g, and the design shows excellent scalability, reaching similar velocities across different projectile sizes. In the past, velocity measurements have been limited to muzzle velocity obtained via a high-speed videography upon the projectile exiting the launch tube. Recently, Photon Doppler Velocimetry (PDV) has demonstrated the ability to continuously measure in-bore velocity, even in the presence of significant blow-by of high temperature helium propellant past the projectile. While a single laser system sampled at 40 GS/s with a 13 GHz detector/scope bandwidth is limited to 8 km/s, a two-laser PDV system is developed that uses two lasers operating near 1550 nm to provide velocity measurement capabilities up to 16 km/s with the same bandwidth and sampling rate. The two-laser PDV system is used to obtain a continuous...

Development of multi-component explosive lenses for arbitrary phase velocity generation

The combination of explosives with different detonation velocities and lens-like geometric shaping is a well-established technique for producing phased detonation waves of a desired shape. This technique can be extended to produce nearly arbitrary detonation phase velocities for the purposes of sequentially imploding pressurized tubes, driving Mach disks or directing blast and fragmentation. This paper presents the theoretical development and experimental testing of two types of explosive lenses designed to produce either of these effects.

Implosion-driven technique to create fast shockwaves in high-density gas

Pressurized tubes surrounded by either one or two layers (separated by a secondary tube) of sensitized nitromethane and encased in a thick-walled tube (the tamper) were imploded. The distance between the detonation wave in the explosive and shock wave in the innermost tube were measured (the standoff). A simple model based on hoop stress and acoustic interactions between the tubing was developed and used to predict the standoff distance. At low initial pressures (on the order of 7MPa), results indicate that the secondary tube and two layers of explosive did not prove to significantly increase the standoff. However, at higher pressures (on the order of 10 MPa), standoff was noticeably greater when the secondary tube was inserted between the pressurized tube and the tamper. The measured values are in reasonable agreement with the predictions of the model.