High-speed Photographic Study Research Articles

A numerical simulation and high-speed photographic study of the audio-frequency noise in an analytical ICP source

Numerical simulation and theoretical prediction show that the observed exponential decrease of the a.f. noise frequency with sampling depth in an ICP source result from a coupling effect of vortex dissipation both at torch outlet and sampling gap.

Drop-weight impact ignition of CL-20 crystals caused by trapped gases: A high-speed photographic study

CL-20 explosive has a wide engineering application foresight due to its high energy while is limited by its mechanical sensitivity. In this regard, to study its ignition mechanisms under impact and to determine the main ignition sources, drop-weight experiments on CL-20 explosive crystals were carried out and recorded by a high-speed photography camera. Various configurations, e.g., film, ring, open ring and strips, were designed to explore primary ignition mechanisms and exclude secondary possible sources. The results show that the main ignition mechanism of CL-20 under drop-weight impact is the adiabatic compression of trapped gases. These trapped gases were mainly from the decomposition of CL-20 itself when melting. Our findings indicate that methods focusing on melting suppression should be considered to reduce the CL-20 sensitivity under impact.

High-speed photographic study of vaporclouds from wet droplets and the subsequent solid particles in an inductively coupled plasma

Horizontal ICP with large droplet cloud showing YO and neutral Y emission.

High-speed photographic study of laser damage and ablation

This paper reviews earlier work and describes a photographic investigation of damage produced in glasses, polymers and crystals by Q-switched and non-Q-switched laser pulses. The cameras used in the study include a Wollensak Fastax WF3 camera, a Beckman & Whitley (model 189) rotating mirror camera, and a Beckman & Whitley (model 501) image converter camera. The formation of internal disc-type cracks with the non-Q-switched pulse was studied in detail. The use of these cracks for fracture energy studies is demonstrated. Photographic sequences show the production of micro-plasmas associated with damage, and stress waves formed during irradiation in both solids and liquids. A recent development is that of digital holography which adds phase and intensity information to the more conventional photographic techniques. This technique is used here to study laser ablation and wave propagation in water. The photographic data shows the processes taking place in the laser interaction with a wide range of materials and should be of interest to modellers.

High-Speed Photographic Study of Chip Formation during End Milling of GFRP Composites

The chip forming process during end milling of glass fibre reinforced composites has been investigated in this study. The qualitative results from a high speed video camera has showed that discontinuous and fracturing of chips has been created due to the heterogeneity and insufficient ductility of the composite materials. The high-speed photography footage has also disclosed that a layer of delaminated chip can be formed as the tool cutting edge fractured the workpiece along the fibre orientation. The fracture of chips into smaller segments accelerated as the cutting speed increases. Likewise, shorter fragment of chips were created as the tool cut at different fibre orientation or angle. This makes it difficult to denote any chip formation processes during the end milling experiments.

Studies of cavitation and ice nucleation in ‘doubly-metastable’ water: time-lapse photography and neutron diffraction

High-speed photographic studies and neutron diffraction measurements have been made of water under tension in a Berthelot tube. Liquid water was cooled below the normal ice-nucleation temperature and was in a doubly-metastable state prior to a collapse of the liquid state. This transition was accompanied by an exothermic heat release corresponding with the rapid production of a solid phase nucleated by cavitation. Photographic techniques have been used to observe the phase transition over short time scales in which a solidification front is observed to propagate through the sample. Significantly, other images at a shorter time interval reveal the prior formation of cavitation bubbles at the beginning of the process. The ice-nucleation process is explained in terms of a mechanism involving hydrodynamically-induced changes in tension in supercooled water in the near vicinity of an expanding cavitation bubble. Previous explanations have attributed the nucleation of the solid phase to the production of high positive pressures. Corresponding results are presented which show the initial neutron diffraction pattern after ice-nucleation. The observed pattern does not exhibit the usual crystalline pattern of hexagonal ice [I(h)] that is formed under ambient conditions, but indicates the presence of other ice forms. The composite features can be attributed to a mixture of amorphous ice, ice-I(h)/I(c) and the high-pressure form, ice-III, and the diffraction pattern continues to evolve over a time period of about an hour.

A NEW BIOMECHANICAL HEAD INJURY CRITERION

This paper presents a new analysis of the physics of closed head injury caused by intense acceleration of the head. At rest a 1 cm gap filled with cerebrospinal fluid (CSF) separates the adult human brain from the skull. During impact, whole head acceleration induces artificial gravity within the skull. Because its density differs slightly from that of CSF, the brain accelerates, strikes the inner aspect of the rigid skull, and undergoes viscoelastic deformation. Analytical methods for a lumped parameter model of the brain predict internal brain motions that correlate well with published high-speed photographic studies. The same methods predict a truncated hyperbolic strength-duration curve for impacts that produce a given critical compressive strain. A family of such curves exists for different critical strains. Each truncated hyperbolic curve defines a head injury criterion (HIC) or threshold for injury, which is little changed by small offsetting corrections for curvature of the brain and for viscous damping. Such curves predict results of experimental studies of closed head injury, known limits for safe versus dangerous falls, and the relative resistance of smaller versus larger animals to acceleration of the head. The underlying theory provides improved understanding of closed head injury and better guidance to designers of protective equipment and to those extrapolating research results from animals to man.

A high-speed photographic study of fast cracks in shocked diamond

Six fracture surfaces have been observed extending at velocities between cR (the Rayleigh wave velocity) and 1.3cR in high-speed photographs of four diamond specimens. The diamonds were embedded in a transparent polymer and shocked in plate impact experiments. The measured velocities exceed limiting velocities proposed in theoretical and practical studies of single mode I cracks in diamond. The fracture surfaces probably extend by initiation and coalescence of multiple tensile fractures along a single cleavage plane. This mechanism is dependent on the suppression of cracks branching from the {111} growth plane in diamond and considers the population of flaws near a propagating crack tip.

BRAIN MOTION AND DEFORMATION DURING CLOSED HEAD INJURY IN THE PRESENCE OF CEREBROSPINAL FLUID

This paper presents a new analysis of the physics of closed head injury following brief, intense acceleration of the head. It focuses upon the buoyancy of the brain in cerebrospinal fluid, which protects against damage; the propagation of strain waves through the brain substance, which causes damage; and the concentration of strain in critical anatomic regions, which magnifies damage. Numerical methods are used to create animations or "movies" of brain motion and deformation. Initially, a 1 cm gap filled with cerebrospinal fluid (CSF) separates the brain from the skull. Whole head acceleration induces artificial gravity within the skull. The brain accelerates, because its density differs slightly from that of CSF, strikes the inner aspect of the skull, and then undergoes viscoelastic deformation. The computed pattern of brain motion correlates well with published high-speed photographic studies. The sites of greatest deformation correlate with sites of greatest pathological damage. This fresh biomechanical analysis allows one to visualize events within the skull during closed head injury and may inspire new approaches to prevention and treatment.

High-speed photographic study of the drop-weight impact response of RDX/DOS mixtures

This paper describes dropweight experiments performed on conventional and ultrafine cyclotrimethylene trinitramine (RDX) to which was added various percentages of the binder dioctyl sebacate (DOS). The ultrafine material particle size was less than 1 μm, while the conventional was 400 μm. The first aim of these experiments was to investigate the effect on the deformation, ignition behavior and impact sensitivity when DOS was added. A further aim was to determine possible sources of ignition in this energetic system. Techniques used included optical microscopy, heat sensitive film, and high-speed photography. The DOS was found to coat the individual particles of RDX. However, under impact loading, the DOS produced a blocky texture of millimeter dimensions. When ignition took place, the primary mechanism was localized adiabatic shear banding.

A Model for the Contact Conditions at the Chip-Tool Interface in Machining

A high-speed photographic study has been made of the chip-tool interface and its evolution when cutting pure metals with optically transparent sapphire tools. The use of a high speed camera in conjunction with an optical microscope has enabled details of the interface, including the velocity field along the interface, to be resolved at high spatial and temporal resolution while cutting at speeds between 1 mm/sec and 2000 mm/sec. The results show the chip-tool contact along this interface to be composed of four distinct regions: a region of stagnation at the cutting edge, a region of retardation adjoining the stagnation region, a region of sliding beyond the retardation region, followed by a region of metal transfer or “sticking” that is located furthest away from the cutting edge alongside the boundary of the contact. The chip and tool appear to be in intimate contact over the stagnation, retardation, and sliding regions, with sliding occurring at the interface over much of this zone of intimate contact. These observations have provided direct experimental evidence for a model of the contact conditions proposed by Enahoro and Oxley based on analytical considerations. Cutting experiments with non-oxide tools such as aluminum and high speed steel suggest that this description conditions is equally applicable to tool materials other than sapphire.

High-speed digital photographic study of an inductively coupled plasma during laser ablation: comparison of dried solution aerosols from a microconcentric nebulizer and solid particles from laser ablation

High-speed photographs and videos of an ICP are used to examine the fates of solid particles produced by laser ablation (LA) in an inductively coupled plasma (ICP). The trajectories, lifetimes, and emission behavior of particles traversing the plasma are studied under a variety of conditions. Desolvated particles from a nebulized yttrium solution and particles ablated from a Y2O3 pellet are mixed and introduced simultaneously into an ICP. High-resolution digital photographs and video sequences are captured using shutter speeds of approximately 65 µs. The plasma behavior of particles generated by a quadrupled Nd:YAG laser (266 nm) and an ArF excimer laser (193 nm) are compared, and either argon or helium is used as the transport gas through the ablation cell. No red emission clouds from YO are visible in the ICP when a 20 µL min−1 nebulizer is used to spray a 2000 ppm aqueous Y solution, suggesting that the wet droplets from this nebulizer desolvate almost completely before entering the ICP. These desolvated particles from the nebulized solution atomize and ionize like the small dry particulates from laser ablation. However, many large ablated particulates are observed to fly through the plasma intact, possibly contributing to signal noise, deposition on the sampler and skimmer cones, and elemental fractionation.

High-speed photographic study of the drop-weight impact response of ultrafine and conventional PETN and RDX

This paper describes a series of drop-weight experiments performed on pentaerythritol tetranitrate (PETN) and cyclotrimethylene trinitramine (RDX). Both chemicals were available in a conventional grain size (10–200 μm for PETN, 30–500 μm for RDX) and in a novel ultrafine particle size (<1 μm). The aim of the study was to determine the relative sensitivity of the four materials and to investigate the mechanisms by which ignition occurred in the samples. Heat sensitive film and high-speed photography revealed adiabatic shear bands in all four materials. However, trapped gas appeared to be the main reason for ignition. Because ultrafine powders have smaller interstices between grains, this could explain why the ultrafine samples were less susceptible to drop-weight impact.

Studies on energetic compounds: Part 16. Chemistry and decomposition mechanisms of 5-nitro-2,4-dihydro-3H-1,2,4-triazole-3-one (NTO)

The present review deals with the chemistry and thermolysis of NTO and plausible decomposition pathways have been described. The decomposition of 5-nitro-2,4-dihydro-3H-1,2,4-triazole-3-one (NTO) induced by X-ray, UV, laser, photochemical irradiation has also been discussed. High-speed photographic studies of the impact responses of NTO are also included. The thermal decomposition of labelled NTO has also been described here. Methods of detection as well as safe disposal of NTO have also been mentioned.

High-speed photography of low-velocity impact cracking of solid spheres

Results from a high-speed photographic study of low-velocity impact cracking of optically transparent acrylic resin and poly(methyl methacrylate) spheres of 12.7mm diameter are described. It is shown that, in a sphere undergoing an impact, cracking occurs after the sphere has been plastically deformed. The point of initiation of cracking is shown to be located at the circle of contact between the sphere and the impacting platen. The cracking then develops throughout the sphere, with cracks attaining velocities of 600-800ms-1. It has been suggested that crack initiation at the contact circle is caused by the tensile circumferential stress, which is generated owing to the plastic flow of the sphere.

Crack bifurcation in disintegrating Prince Rupert's drops

Results from a high-speed photographic study made at a framing speed of one million frames per second of the disintegration of Prince Rupert's drops made of soda-lime glass and immersed in a transparent liquid of a matching refractive index are described. The refractive index matching made the cracks through the drop and their bifurcation very clearly visible. The results further confirm a model of the disintegration process proposed recently.

A high-speed photographic study of the impact initiation of hexanitro-hexaaza-isowurtzitane and nitrotriazolone

A high-speed photographic study has been performed of the initiation mechanisms of hexanitro-hexaaza-isowurtzitane (CL-20) and nitrotriazolone (NTO) by drop-weight impact. CL-20 was found to be slightly more sensitive and NTO less sensitive than cyclotetramethylene tetranitramine (β-HMX) in our drop-weight apparatus. NTO was found to be sensitised by both hard-high-melting point grits (60 μm borosilicate or pyrex glass) and brittle polymers. Heat-sensitive film was used to confirm that the events seen using high-speed photography were indeed deflagration.

A High-Speed Photographic Study of the Rapid Deformation of Metal Annuli : Comparison of Theory with Experiment

Pour verifier le modele de comportement d'un metal, il est important de determiner comment il faut corriger les courbes contrainte-deformation obtenues en compression afin de tenir compte des effets de frottement. Des erreurs graves viennent d'etre decouvertes dans les modeles analytiques standards utilises pour determiner les dites corrections dans les barres de Hopkinson. Dans le present article nous proposons une nouvelle methode pour determiner le coefficient de frottement dans la compression axiale dynamique d'un anneau La methode utilise la modelisation numerique et la photographie ultrarapide. Elle est validee en utilisant un acier a blindage.

Experimental comparisons with a numerical model of surfactant effects on the burst of a single bubble

A high-speed photographic study of gas bubbles bursting at a gas/liquid interface in the presence of surfactant is described. Bubbles were burst in a variety of media typical of those used in mammalian cell culture. In order to test the hypothesis that surfactant reduces cell damage as a result of moderation of the bubble burst, a numerical simulation of the surfactant effect was compared with the experimental data. Surface tension, surface shear and dilatational viscosities were measured in a variety of media containing a surfactant. The rate of bubble jet rise, a readily measured property of a burst, which depends strongly on the presence of surfactant, was measured. Experimental observations in the presence of surfactant broadly agree with the theory in the reduction in jet rise rate, if it is assumed that dilatational viscosity plays a major role. However, measured values for surface dilatational viscosity were an order of magnitude less than those required for an observable effect in the model. A reason for this discrepancy is proposed.

High-Speed Photographic Study of the Impact Response of Ammonium Dinitramide and Glycidyl Azide Polymer

A high-speed photographic study has been performed of the rapid deformation of ammonium dinitramide (ADN) and glycidyl azide polymer (GAP) by drop-weight impact. ADN was found to be more sensitive than ammonium perchlorate. Both materials have been suggested as potentially useful oxidizers in explosive and propellant applications. ADN was also found to be sensitized by both hard high-melting point grits (60-mm borosilicate or Pyrext glass) and brittle polymers. High-density polyethylene was found to suppress de agration in this material. Heat-sensitive Ž lm was used to conŽ rm that the events seen using high-speed photography were indeed de agrations. GAP was found to be insensitive when impacted in this apparatus, even in the presence of additives or gas bubbles.