24 research outputs found
Synchrotron X-ray phase-contrast imaging of ultrasonic drop atomization
Ultrasonic atomization is employed to generate size-controllable droplets for
a variety of applications. Here, we minimize the number of parameters dictating
the process by studying the atomization of a single drop pending from an
ultrasonic horn. Spatiotemporally resolved X-ray phase-contrast imaging
measurements show that the number-median sizes of the ejected droplets can be
predicted by the linear Navier-Stokes equations, signifying that the size
distribution is controlled by the fluid properties and the driving frequency.
Experiments with larger pendant water drops indicate that the fluid-structure
interaction plays a pivotal role in determining the ejection onset of the
pendant drop. The atomization of viscoelastic drops is dictated by extended
ligament formation, entrainment of air, and ejection of drop-encapsulated
bubbles. Existing scaling laws are used to explain the required higher input
amplitudes for the complete atomization of viscoelastic drops as compared to
inviscid drops. Finally, we elucidate the differences between capillary
wave-based and cavitation-based atomization and show that inducing cavitation
and strong bubble oscillations quickens the onset of daughter drop ejection but
impedes their size control.Comment: 36 pages, 11 figure
In situ damage characterization of CFRP under compression using high-speed optical, infrared and synchrotron X-ray phase-contrast imaging
The strain rate dependency and failure modes of carbon fiber reinforced plastic (CFRP) laminate were investigated under out-of-plane compressive loading. Simultaneous high-speed optical and infrared imaging were used to measure full-field deformation and temperature in the dynamically loaded specimens. The damage initiation and propagation inside the CFRP laminates at high strain rates were characterized using in-situ ultra-fast synchrotron X-ray phase contrast imaging (XPCI). The visually observed damage onset occurs at the strain value of 4.2 ± 0.6% as a transverse shear fracture at the free edge of specimens. The local temperature increases significantly to 185 °C due to damage initiation at high strain rates, while at low strain rates the temperature rise occurs after the final shear band forms. The XPCI and post-failure analysis provide an integrated perspective on the formation of a diagonal shear crack and disintegration of the specimen into two pieces with the fracture of plies in the in-plane transverse direction. Scanning electron microscopic (SEM) study was integrated with XPCI results to append the time scale for the post-mortem failure pattern as well as the length scale for microcracks and filament-level failure.Peer reviewe
Ultrafast Radiographic Imaging and Tracking: An overview of instruments, methods, data, and applications
Ultrafast radiographic imaging and tracking (U-RadIT) use state-of-the-art
ionizing particle and light sources to experimentally study sub-nanosecond
dynamic processes in physics, chemistry, biology, geology, materials science
and other fields. These processes, fundamental to nuclear fusion energy,
advanced manufacturing, green transportation and others, often involve one mole
or more atoms, and thus are challenging to compute by using the first
principles of quantum physics or other forward models. One of the central
problems in U-RadIT is to optimize information yield through, e.g.
high-luminosity X-ray and particle sources, efficient imaging and tracking
detectors, novel methods to collect data, and large-bandwidth online and
offline data processing, regulated by the underlying physics, statistics, and
computing power. We review and highlight recent progress in: a.) Detectors; b.)
U-RadIT modalities; c.) Data and algorithms; and d.) Applications.
Hardware-centric approaches to U-RadIT optimization are constrained by detector
material properties, low signal-to-noise ratio, high cost and long development
cycles of critical hardware components such as ASICs. Interpretation of
experimental data, including comparisons with forward models, is frequently
hindered by sparse measurements, model and measurement uncertainties, and
noise. Alternatively, U-RadIT makes increasing use of data science and machine
learning algorithms, including experimental implementations of compressed
sensing. Machine learning and artificial intelligence approaches, refined by
physics and materials information, may also contribute significantly to data
interpretation, uncertainty quantification and U-RadIT optimization.Comment: 51 pages, 31 figures; Overview of ultrafast radiographic imaging and
tracking as a part of ULITIMA 2023 conference, Mar. 13-16,2023, Menlo Park,
CA, US
Measurement of fracture energy of a high performance concrete in dynamic tension and high strain rates
International audienceThis paper presents the experimental results of the dynamic fracture energy of HPC measured via the photomechanical spalling test. Full field measurements are performed and the stress-fracture opening displacement curves are obtained for each visualized fracture zone from which the specific fracture energy can be calculated. First results obtained from several spalling tests were found to be lower than what is reported in the literature
Validation of the photomechanical spalling test in the case of non‐linear dynamic response: Application to a granite rock
International audienc
Use of simulated experiments for identification of concrete damage response during high strain rate dynamic tension
International audienc
Evaluation of a full-field measurement method used to identify the dynamic fracture energy of concrete based on simulated experiments
International audienc
Experimental study of the dynamic behaviour of High Performance Concrete (HPC) under tensile loading
International audienc
On the use of the Virtual Fields Method and Ultra High Speed Photography to characterize spalling strength of ordinary concrete
International audienc
Cavitation cloud formation and surface damage of a model stone in a high-intensity focused ultrasound field
This work investigates the fundamental role of cavitation bubble clouds in stone comminution by focused ultrasound. The fragmentation of stones by ultrasound has applications in medical lithotripsy for the comminution of kidney stones or gall stones, where their fragmentation is believed to result from the high acoustic wave energy as well as the formation of cavitation. Cavitation is known to contribute to erosion and to cause damage away from the target, yet the exact contribution and mechanisms of cavitation remain currently unclear. Based on in situ experimental observations, post-exposure microtomography and acoustic simulations, the present work sheds light on the fundamental role of cavitation bubbles in the stone surface fragmentation by correlating the detected damage to the observed bubble activity. Our results show that not all clouds erode the stone, but only those located in preferential nucleation sites whose locations are herein examined. Furthermore, quantitative characterizations of the bubble clouds and their trajectories within the ultrasonic field are discussed. These include experiments with and without the presence of a model stone in the acoustic path length. Finally, the optimal stone-to-source distance maximizing the cavitation-induced surface damage area has been determined. Assuming the pressure magnitude within the focal region to exceed the cavitation pressure threshold, this location does not correspond to the acoustic focus, where the pressure is maximal, but rather to the region where the acoustic beam and thereby the acoustic cavitation activity near the stone surface is the widest