High-speed Digital Photography Research Articles

High-Speed Digital Photography of Vapor Cavitation in a Narrow Gap Flow

Digital photography of cavitation in narrow gap flows, e.g., lubrication films in journal bearings or squeeze film dampers, demands a high time-resolution and a solution to approaching the particular spatial restrictions. Typically, the lubrication film thickness is in the range of a few microns and the characteristic time for vapor bubble generation and collapse is about one millisecond, respectively. The authors have developed a Journal Bearing Model Experiment, which is designed according to similarity laws providing fully similar flow conditions to real journal flows while offering ideal access to the flow by means of optical measurement equipment. Compared with other methods, e.g., pulsed laser, electrical discharge, tube arrest, applied to produce vapor bubbles, the work on hand applies a dynamic variation of the minimum film thickness to produce suction cavitation, which proves the applicability of this novel approach to study vapor cavitation in fluid films similar to lubricant flows. The results are obtained by means of digital high-speed photography of vapor bubbles from inception to implosion triggered by the dynamic variation of the minimum film thickness of a narrow gap flow. Moreover, the results are set in relation to a general overview of cavitation processes.

In-process measurement of mechanical loads during electrical discharge machining

In electrical discharge machining, in-process measurements of the induced mechanical stress are essential to develop process models for improving the fatigue strength of the machined part. For this purpose, high-speed digital speckle photography is introduced to measure the workpiece-side load fields with a lateral displacement resolution of 28 nm at a spatiotemporal resolution of 29 µm and 40 µs, respectively. As a result, the load effects of even individual 100 µs short discharge pulses are temporally resolved for the first time, and the occurring spatial load inhomogeneities and their dynamics are characterized to complement our understanding of the machining process.

High-Speed Digital Photography of Gaseous Cavitation in a Narrow Gap Flow

The research of cavitation in narrow gap flows, e.g., lubrication films in journal bearings or squeeze film dampers, is a challenging task due to spatial restrictions combined with a high time-resolution. Typically, the lubrication film thickness is in the range of a few microns and the characteristic time for bubble generation and collapse is less than a few milliseconds. The authors have developed a journal bearing model experiment, which is designed according to similarity laws providing fully similar flow conditions to real journal flows while offering ideal access to the flow by means of optical measurement equipment. This work presents the high-speed photography of bubble evolution and transportation in a Stokes-type flow under the influence of shear and a strong pressure gradient which are typical for lubricant films. A paramount feature of the experiment is the dynamic variation (increase/decrease) of the minimum film thickness which triggers the onset of cavitation in narrow gap flows. Results presented in the work on hand include the time-resolved data of the gas release rate and the transient expansion of gas bubbles. Both parameters are necessary to set up numerical models for the computation of two-phase flows.

Development of an Easily Reproducible Cough Simulator With Droplets and Aerosols for Rapidly Testing Novel Personal Protective Equipment.

The current COVID-19 pandemic has produced numerous innovations in personal protective equipment, barrier devices, and infection mitigation strategies, which have not been validated. During high-risk procedures such as airway manipulation, coughs are common and discrete events that may expose healthcare workers to large amounts of viral particles. A simulated cough under controlled circumstances can rapidly test novel devices and protocols and thus aid in their evaluation and the development of implementation guidelines. Physiologic cough simulators exist but require significant expertise and specialized equipment not available to most clinicians. Using components commonly found in healthcare settings, a cough simulator was designed for clinicians to easily assemble and use. Both droplet and aerosol particle generators were incorporated into a bimodal experimental system. High-speed flash photography was used for data collection. Using a gas flow analyzer, video recordings, and high-speed digital photography, the cough and particle simulators were quantitatively and qualitatively compared with known physiologic cough parameters and in vivo Schlieren imaging of human coughs. Based on our validation studies, this cough and particle simulator model approximates a physiologic, human cough in the context of testing personal protective equipment, barrier devices, and infection prevention measures.

Flow structures of over-expanded supersonic gaseous jets for deep-water propulsion

Supersonic gaseous jets with large ambient pressure are typically found in deep-water propulsion systems. The interactions between gas and water are turbulent, and the plume exhibits unstable bubbly interfaces. This work employed both experimental and numerical methods to obtain the flow structures of over-expanded gaseous jets driven by different pressure ratios in water. Direct measurements of the interfacial behaviour of submerged gaseous jets with pressurised water, were performed using high-speed digital photography. Numerical simulations were also conducted to characterise flow structures by the interplay of inertia and buoyancy forces. It was found that the interface of injection into water showed continuous fluctuations and strong mixing in the conical regions. The intermittent expansion-necking characteristics just beyond the nozzle exit, induced the pressure oscillation of the flow field near the wall, localised liquid water attack of the exit wall, and aggravated the over-expansion of nozzle working conditions. These periodic phenomena were attributed to Kelvin-Helmholtz (K–H) instabilities, driven by the large gradients of velocity and density in the shearing layers. The oscillation characteristics were assessed at different ambient pressures, providing theoretical support for the design of engineering devices working over a wide range of water depths.

Biophysical and chemical stability of surfactant/budesonide and the pulmonary distribution following intra-tracheal administration

Intra-tracheal instillation of budesonide using surfactant as a vehicle significantly decreased the incidence of bronchopulmonary dysplasia or death in preterm infants. The formularity of surfactant supplemented with budesonide and biophysical and chemical stability of the suspension has not been well reported. The aims are to investigate the biophysical and chemical stability of two surfactant preparations, Survanta and Curosurf, supplemented with budesonide. Biophysical property of the surface tension of Survanta and Survanta/budesonide suspension and of Curosurf and Curosurf/budesonide suspension was conducted by a pulsating bubble surfactometer and by a drop shape tensiometer. Chemical stability of Survanta/budesonide and of Curosurf/budesonide suspensions was tested by high-performance liquid chromatography analysis (HPLC). Pulmonary distribution of Survanta/18F-budesonide suspension was examined by a Nano/PET digital scan in rats. The Marangoni effect of Survanta, Curosurf, and budesonide was tested by digital high speed photography. For Survanta supplemented with budesonide, with a concentration ratio of ≥50, the surface tension-lowering activity was minimally affected. Similarly, the surface tension-lowering activity of Curosurf was not significantly affected by addition of budesonide, if the concentration ratio was ≥160. With these concentration ratios of both suspensions, HPLC analysis revealed no new compounds identified. Curosurf as compared to Survanta exhibited a significantly higher Marangoni effect. We conclude that with current dosage recommended for Survanta and Curosurf, both surfactant/budesonide suspensions are biophysically and chemically stable. Both surfactants can act as an effective vehicle for budesonide delivery.

Research on measuring method of shot exit time for muzzle vibration analysis

The measurement of shot exit time is very important to measuring data analysis of muzzle vibration. Optoelectronic method, which is based on the optical-electrical conversion theory and timed with the muzzle flame, is a general method of measuring the shot exit time for the major caliber gun. However, it has not been identified that the shot exit time corresponds to which characteristic point in the voltage pulse time signal curve obtained by the optoelectronic method. In this paper, by combining the high speed digital photography and the optoelectronic method, both the triggering time signal of the high speed digital photography and the voltage signal output by the optoelectronic sensor were obtained simultaneously. Then by comparing the voltage time curve of the optoelectronic sensor with the photographs obtained by the digital photography, the relationship between the characteristic points in the signal curve and the shot exit time was identified. It has been shown that, the voltage pulse beginning time is the same with the muzzle flame beginning, which is later than the time when the projectile band leaves from muzzle.

The Dynamics of Blood Drop Release from Swinging Objects in the Creation of Cast-off Bloodstain Patterns.

Although the characteristics of cast-off bloodstain patterns are well known, the physics of the mechanism by which they are created is poorly understood. The aim of this work was to describe the process by which blood droplets disengage from swinging objects. Cast-off droplets were recorded using high-speed digital video photography, and the resulting cast-off patterns were analyzed to draw inferences about the trajectories of individual drops. Blood on the object's distal end formed ligaments, which subsequently disintegrated into droplets. Initial droplet trajectories were approximately tangential to the trajectory of the location on the object from which the droplet was released. The application of the laws of physics to the mechanism of cast-off is discussed, and the process of drop formation is compared to that of passive drop formation. A technical description of cast-off is proposed, and a diagram to aid investigators in interpreting cast-off patterns at crime scenes is offered.

High-speed 3D digital image correlation of low-velocity impacts on composite plates

Abstract Composites are beginning to be used in a variety of different applications throughout industry. However, certification and damage tolerance is a growing concern in many aerospace and marine applications. Transverse impact of composites results in damage in the form of transverse matrix crack, delamination, fiber breakage and permanent deformation. Low-velocity impact experiments were conducted on 3.2 mm thick IM7/977-3 composites with 10 J of energy (1.888 m/s). High-speed digital photography was used to capture impact phenomenon of a composite's back surface. The specimens were speckled to perform 3D digital image correlation to analyze the displacements and strains that occurred on the back surface. The results from this study provide basic knowledge of the impact event such as deformation, strains, residual strains, damage threshold load, transverse matrix crack initiation and propagation.

Particle movements in near field induced by thick-wall effect in a dense gas-solid coaxial jet

A particle entrainment phenomenon in the near field is observed in a dense gas-solid coaxial jet due to the thick-wall effect. Particle movements induced by annular gas backflow in the recirculation region are experimentally studied using high-speed digital photography. The experimental results reveal the tendency of the entrained particle velocity with annular gas velocity increasing and Reg=2.9×104 is proposed to determine the emergence of the largest entrained particle velocity. An increase of nozzle wall thickness is proved to enhance the recirculation of annular gas stream and accelerate entrained particles to collide with the nozzle wall. Additionally, the particle mass flow rate has a slightly influence on the entrained particle velocity. In the particle entrainment phenomenon, interactions between gas and particles greatly depend on drag force of annular gas backflow on entrained particles. Base on the gas-solid dynamic model and the drag model modified by the wake effect, a correlation of the entrained particle velocity is proposed.

Effect of fibre-matrix interfacial strength on the explosive blast resistance of carbon fibre laminates

The influence of the fibre-polymer matrix interfacial bond strength on the explosive blast response of carbon fibre laminates is experimentally investigated. Air blast tests were performed on laminate target panels containing woven carbon fabric treated with a fibre-sizing agent that promoted either weak or strong bonding with the polymer matrix. The laminates were subjected to increasing shock wave impulse loads by increasing the mass or reducing the stand-off distance of the plastic explosive charge. High-speed digital image correlation photography (DIC) during explosive blast testing revealed the dynamic deformation responses and surface strains of the laminate targets were not influenced significantly by the type of fibre-sizing agent, except at high shock wave impulse levels. However, non-destructive testing using ultrasonics and X-ray computed tomography revealed that the initiation and growth of blast-induced damage (e.g. delamination cracks, matrix cracks, fibre fracture) was dependent to the interfacial bond strength. Damage occurred at a high shock impulse level in the laminate with strong fibre-matrix interfacial bonding, and this is attributed to higher flexural and interlaminar fracture toughness properties compared to the composite with weak interfacial bonding. The post-blast mechanical properties were also higher for the laminate with strong interfacial bonding. This study reveals that the fibre-sizing agent has a substantial influence on the explosive blast resistance and post-blast properties of laminates, and it is essential that an agent having high chemical compatibility with the polymer matrix is used to promote strong bonding.

Experimental and analytical study of the dynamic debonding in FRP plated beams

This paper presents an experimental study of the dynamic debonding failure mechanism in FRP plated beams. The experimental study is accompanied by an analytical/numerical study. The focus in the experimental investigation is on the dynamic aspects of the brittle, rapid, and abrupt failure mechanism and on its characterization and quantification. The experimental technique is based on four point bending tests of FRP plated steel beam specimens. The main dynamic monitoring technique uses high-speed digital photography with rate of 88,050 frames per second. The analytical and numerical aspects of the investigation use an extended high order layered beam theory with a physical modeling resolution that considers nucleation and evolution of the debonding mechanism in each physical interface. This is achieved by using cohesive interfaces and a specially tailored finite element formulation that is based on the theory. Digital image processing of the experimental results reveals and quantifies the dynamics of the interfacial failure with propagation velocities in the order of 100–1000 m/s and duration of less than 0.2 ms. The results reveal the dynamic nature of the failure process and provide an experimental benchmark for its consideration. They also provide direct experimental data for supporting and validating the theory and for determining the fracture energy and length scale parameters of the cohesive interfaces. With that, the combined experimental and theoretical study further explores the dynamic features of the failure mechanism.

Leidenfrost Droplets on Microstructured Surfaces

The lifetime of a droplet deposited on a hot plate decreases when the temperature of the plate increases, but above the critical Leidenfrost temperature, the lifetime suddenly increases. This is due to the formation of a thin layer of vapor between the droplet and the substrate, which plays a double role: First, it thermally insulates the droplet from the plate, and second, it allows the droplet to “levitate.” The Leidenfrost point is affected by the roughness or microstructure of the surface. In this work, a silicon surface with different microstructured regions of square pillars was prepared such that there is a sharp transition (boundary) between areas of different pillar spacing. The Leidenfrost point was identified in experiments using water droplets ranging in size from 8 to 24 μl and the behavior of the droplets was recorded using high-speed digital photography. The Leidenfrost point was found to vary by up to 120°C for pillar spacings from 10 to 100 μm. If the droplet is placed on the boundary between structured sections, the droplet becomes asymmetric and may move or spin. An axisymmetric computational fluid dynamics (CFD) model is also presented that shows qualitative agreement with experimental observations.

Fragmentation of wedge loaded tempered structural glass

A high-speed study of tempered glass fracture propagation is presented. Tempered glass is used worldwide both architecturally and in the automotive industry, often playing a role in structural integrity. To accurately predict the brittle failure of the structural elements, it is essential to study crack initiation and formation. Cracks were initiated using a concentrated force employing a steel wedge. To capture abrupt crack propagation, digital high-speed photography was used with 50,000 frames per second and $$180\times 132$$ pixels. A theoretical method based on fracture mechanics was developed and verified with experimental results. A correlation was found between the relative resistance of the specimens and the plate thickness. Which was explained by the difference in the tempered stress field between specimens. The fracture pattern close to the wedge started from a single crack which branched repeatedly after 0.6–0.8 cm, indicating a uniformly increasing energy release. Then using the governing fracture pattern and the stress field measured with a scattered light polariscope, a linear elastic fracture mechanics approach defined the energy release ratio. This parameter was found linearly dependent as a function of plate thickness. Applying this ratio as a known value, the fragment count standard (e.g. EN 12150-1:2000, Glass in building. Thermally toughened soda lime silicate safety glass. Definition and description, 2000) can be fine-tuned to be used not only for safety purposes but for thermal stress measurement as well. Thus, this could supplement the four point bending test [EN 1288-3:2000, Glass in building—determination of the bending strength of glass—Part 3: test with specimen supported at two points (four-point bending), 2000], where the effective tensile strength is measured only. Interestingly, the method developed could reduce overhead costs for companies by replacing the use of expensive machinery to measure stress in structural tempered glass elements.

Synthesis, Characterization and Evaluation of Urethane Co-Oligomers Containing Pendant Fluoroalkyl Ether Groups.

Coatings with the ability to minimize adhesion of insect residue and other debris are of great interest for future aircraft. These aircraft will exhibit increased fuel efficiency by maintaining natural laminar flow over greater wing chord distances. Successful coatings will mitigate the adhesion of debris on laminar flow surfaces that could cause a premature transition to turbulent flow. The use of surface modifying agents (SMA) that thermodynamically orient towards the air side of a coating can provide specific surface chemistry that may lead to a reduction of contaminate adhesion. Aluminum surfaces coated with urethane co-oligomers containing various amounts of pendant fluoroalky ether groups were prepared, characterized and tested for their abhesive properties. The coated surfaces were subjected to controlled impacts with wingless fruit flies (drosophila melanogaster) using both a benchtop wind tunnel and a larger-scaled wind tunnel test facility. Insect impacts were recorded and analyzed using high-speed digital photography and the remaining residues characterized using optical surface profilometry and compared to that of an aluminum control. It was determined that using fluorinated oligomers to chemically modify coating surfaces altered the adhesion properties relative to the adhesion of insect residues to the surface.

Storage life of whole porcine blood used for bloodstain pattern analysis

ABSTRACTBloodstain pattern analysis (BPA) can be critical for criminal investigations, for example by providing information on the events that have occurred. Reconstruction and scientific experiments conducted to understand such bloodstain patterns are multifaceted. An important variable that needs to be controlled is the blood source. In the BPA community it would be useful to know if storage conditions affect the properties of blood and any associated bloodstains. Knowing this would assist in appropriate experimental design for research and reconstruction purposes. The aim of this study was to investigate the effects of storage time and intraspecific variation of blood from different pigs on selected hematological properties (packed cell volume and plasma protein concentration), drop diameter and drip stain size of whole porcine blood with a liquid anticoagulant. Drip stains were generated from four different pigs' blood samples, and documented with high-speed video and digital photography. Significant changes in packed cell volume, drop diameter, drip stain size and spreading ratio during storage (25 days) were identified using multilevel linear models. While a time-frame for storing blood was not established, the complexity of the degradation and ageing of the stored blood became apparent. It is recommended that studies which seek to compare drip stain characteristics using blood stored over several days should include steps to monitor changes in blood properties with time and employ the use of a standard control surface to determine changes in stain characteristics over the duration of the experiment.

Peculiarity of Solitary Deflection Waves Dynamics on the Domain Walls of Yttrium Orthoferrite

The solitary deflection waves accompany moving antiferromagnetic vortices in the domain wall of yttrium orthoferrite. These waves allow to investigate generation and nonlinear dynamics of these vortices on the moving domain wall with the help of two-and three-fold digital high speed photography. As the domain walls and the antiferromagnetic vortices dynamics is quasi-relativistic with the limiting velocity c=20 km/s, which is equal to the spin-wave velocity. The dynamics of solitary deflection waves can be explained assuming existence of the gyroscopic force. This work is devoted to experimental results on the dynamics of the solitary deflection waves on the domain wall of yttrium orthoferrite.

Mapping Static and Dynamic Crack-Tip Deformations Using Reflection-Mode Digital Gradient Sensing: Applications to Mode-I and Mixed-Mode Fracture

The reflection-mode digital gradient sensing (r-DGS) method is extended for visualizing and quantifying crack-tip deformations in solids under quasi-static and dynamic loading conditions. The r-DGS technique employs digital image correlation principles to quantify two orthogonal surface slopes simultaneously in specularly reflective solids by measuring small deflections of light rays. Here, for the first time, r-DGS is implemented to study both mode-I and mixed-mode (I/II) problems and evaluate fracture parameters. Under dynamic loading conditions, r-DGS is employed in conjunction with high-speed digital photography to map surface slopes in edge cracked plates subjected to one-point impact. The measured surface slopes are used to successfully evaluate instantaneous stress intensity factor histories by combining measurements with the corresponding asymptotic crack-tip fields and performing over-deterministic least-squares analyses. Finite element computations are also used to complement experimental measurements as needed.

The Measurement of the Fatigue Crack-Tip Displacement and Strain Fields under High Frequency Resonant Loading Applying DIC Method

In order to measure the displacement and strain field in the fatigue crack tip area of CT specimens under high frequency resonant loading condition in the fatigue crack propagation test, a method based on the digital image correlation (DIC) and digital high-speed photography technology are proposed in this paper. First, a series of digital speckle images of CT specimen under sinusoidal alternating load were collected by digital high-speed photography equipment, the displacement and strain fields within the region of crack tip in each image were calculated by DIC. The sinusoidal changing strain curve has been obtained by the least square sine wave fitting method, and the characteristic parameters of sinusoidal strain are calculated, such as the amplitude, frequency, phase, mean load . The images of characteristic position in one stress cycle were obtained by comparing the fitted sine curve of strain with the corresponding speckle images. Finally, the dynamic strain gauge was used to measure the strain at crack tip point during one stress cycle, and the accuracy and feasibility of DIC method were verified by the experimental results. The study result presented in this paper will supply a foundation for exploring the crack propagation law and measuring the fatigue crack growth parameters under high frequency resonant loading condition further.

Oscillation Flow Induced by Underwater Supersonic Gas Jets from a Rectangular Laval Nozzle

In present work, direct measurements of the interfacial behavior of water-submerged gas jets, with nozzle operated in over-expansion to highly under-expansion conditions, were performed using high-speed digital photography. The experimental results show that the two low-frequency oscillations, which are so called jet necking/bulging and necking/back-attack phenomenon, are also found in the region near present rectangular nozzle exit.As the nozzle pressure ratio increased, two distinct flow regimes can be observed: One that showed unstable gas/water interfacial characteristics for nozzle pressure ratio, NPR or Po/Pa≤ 10.17 when the jet pattern showed similar shape as the one issuing from axisymmetric nozzles, and the other with stable jet pattern for NPR > 18.48 when a 3D cross-like cross section jet gas/water boundary started to form and grow from the nozzle exit. Finally, numerical analysis on shockwave structures of the experimental nozzle models was carried out, and the submerged jet gas/water interface characteristics show good agreement with the jet boundaries predicted by numerical simulations. The numerical results indicate that the over-expanded flow in the four corner regions as well as the recompression shock wave may play a dominant role in the interface instability to result in necking/bulging and necking/back-attack phenomenon during over-expanded to slightly under-expanded conditions.