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Porosity in directed energy deposition (DED) deteriorates mechanical performances of components, limiting safety-critical applications. However, how pores arise and evolve in DED remains unclear. Here, we reveal pore evolution mechanisms during DED using in situ X-ray imaging and multi-physics modelling. We quantify five mechanisms contributing to pore formation, migration, pushing, growth, removal and entrapment: (i) bubbles from gas atomised powder enter the melt pool, and then migrate circularly or laterally; (ii) small bubbles can escape from the pool surface, or coalesce into larger bubbles, or be entrapped by solidification fronts; (iii) larger coalesced bubbles can remain in the pool for long periods, pushed by the solid/liquid interface; (iv) Marangoni surface shear flow overcomes buoyancy, keeping larger bubbles from popping out; and (v) once large bubbles reach critical sizes they escape from the pool surface or are trapped in DED tracks. These mechanisms can guide the development of pore minimisation strategies. Porosity is a key issue in additive manufacturing (AM). Here, the authors reveal the bubble evolution mechanisms including formation, coalescence, pushing, growth, entrainment, escape, and entrapment during directed energy deposition AM using in situ X-ray imaging and multiphysics modelling. [ABSTRACT FROM AUTHOR]

Synchrotron X-ray imaging has been utilised to detect the dynamic behaviour of molten pools during the metal additive manufacturing (AM) process, where a substantial amount of imaging data is generated. Here, we develop an efficient and robust deep learning model, AM-SegNet, for segmenting and quantifying high-resolution X-ray images and prepare a large-scale database consisting of over 10,000 pixel-labelled images for model training and testing. AMSegNet incorporates a lightweight convolution block and a customised attention mechanism, capable of performing semantic segmentation with high accuracy (~96%) and processing speed (< 4 ms per frame). The segmentation results can be used for quantification and multi-modal correlation analysis of critical features (e.g. keyholes and pores). Additionally, the application of AM-SegNet to other advanced manufacturing processes is demonstrated. The proposed method will enable end-users in the manufacturing and imaging domains to accelerate data processing from collection to analytics, and provide insights into the processes' governing physics. [ABSTRACT FROM AUTHOR]

The breakup of a liquid jet by a surrounding high-speed gas jet with different liquid Reynolds numbers and gas Weber numbers was studied using high speed phase-contrast X-ray imaging technique. Focusing on the liquid core, the portion of liquid that is connected to the nozzle, four distinct morphologies were observed and can be associated with changes in the large-scale configurations of the two-phase flow are reported in a phase diagram. Gas-to-liquid kinetic energy balance arguments capture several transitions between the liquid core regimes. The temporal evolution of the center of mass of the liquid core is extracted to quantify its motion, whose statistics can be utilized as a signature to distinguish different regimes. At low to moderate gas Weber numbers, the dynamics are strongly influenced by flapping, while long-time dynamics develop at high Weber numbers, that give way to quasi-periodic motions when swirl is impeded to the gas jet. [Display omitted] • Gas-assisted atomization is studied by Synchrotron-based high-speed X-ray. • Phase contrast imaging highlights interfaces and reveals the liquid core morphology. • The morphologies are studied varying both the liquid Reynolds and gas Weber numbers. • Time series of the liquid core center of mass are extracted over long recordings. • Signatures of change in regimes and long-time dynamics emergence are evidenced. [ABSTRACT FROM AUTHOR]

Studying the failure behaviour of engineered or natural materials under dynamic loading scenarios is of high importance, for example to investigate the fracture mechanics and to prevent catastrophic failures of constructions. When dynamic loading is coupled to high-speed X-ray imaging, not only surface information but images of the interior of the specimens during failure are accessible. Here, a custom designed Split Hopkinson Tension Bar (SHTB) coupled a Universal Testing Machine (UTM) has been developed, dedicated to study quasi-static and dynamic response using ultra-high speed X-ray phase contrast imaging. Both systems follow a compact design which allows them to be temporarily installed at a synchrotron beamline. A brief description of the installation and usage of these setups are outlined. Selected example applications outline the potential of these systems. Both systems can be considered for proposal experiments at beamline ID19 of the European synchrotron ESRF on request. [ABSTRACT FROM AUTHOR]

In situ investigations of cracks propagating at up to 2.5 km s-1 along an (001) plane of a silicon single crystal are reported, using X-ray diffraction megahertz imaging with intense and time-structured synchrotron radiation. The studied system is based on the Smart Cut process, where a buried layer in a material (typically Si) is weakened by microcracks and then used to drive a macroscopic crack (10-1 m) in a plane parallel to the surface with minimal deviation (10-9 m). A direct confirmation that the shape of the crack front is not affected by the distribution of the microcracks is provided. Instantaneous crack velocities over the centimetre-wide field of view were measured and showed an effect of local heating by the X-ray beam. The post-crack movements of the separated wafer parts could also be observed and explained using pneumatics and elasticity. A comprehensive view of controlled fracture propagation in a crystalline material is provided, paving the way for the in situ measurement of ultra-fast strain field propagation. [ABSTRACT FROM AUTHOR]

X-ray phase-contrast imaging is an effective approach to drastically increase the contrast and sensitivity of microtomographic techniques. Numerous approaches to depict the real part of the complex-valued refractive index of a specimen are nowadays available. A comparative study using experimental data from grating-based interferometry and propagation-based phase contrast combined with single-distance phase retrieval applied to a non-homogeneous sample is presented (acquired at beamline ID19-ESRF). It is shown that grating-based interferometry can handle density gradients in a superior manner. The study underlines the complementarity of the two techniques for practical applications. [ABSTRACT FROM AUTHOR]

Battery safety design is important to consider from the individual Li-ion cell to the level of the macro-system. On the macro-level, failure in one single cell can lead to propagation of the thermal runaway and rapidly set a whole battery pack on fire. Factors that can impact the propagation outcome, such as cell model/chemistry and electrical connection are here investigated using a combination of measurements. Several abusive tests were conducted, combining two different cell models (Molicel P42A and LG M50, both 21700s) in series and parallel connections (16 tests per configuration). Overall, a propagation outcome of 56% was measured from the 32 conducted tests, a minimum temperature of 150 °C was required to initiate propagation, and the fastest propagation occurred in 123 s. Temperature measurements were higher in series connected cells, initiating the discussion of cell chemistry and internal resistance on this effect. The difference in current-flow during thermal runaway in series and parallel connections, and how this can affect the temperature evolution is further discussed. Spatio-temporal mapping of X-ray radiography allowed us to derive the speed of thermal runaway evolution inside the battery and has shown that series connected cells, in particular P42A, occur faster. It was further observed that deviant sidewall behaviors such as temperature-induced breaches and pressure-induced ruptures occurred in P42As only respective nail-penetrated cells only. • 56% chance of Li-ion battery failure propagation for abusive test scenarios conducted. • Spatio-temporal mapping of Li-ion battery failure from High-Speed X-ray Imaging. • Cell chemistry and electrical connection influence failure temperature and speed. [ABSTRACT FROM AUTHOR]

Prevention and mitigation of hazardous battery failure scenarios can be achieved through the integration of different safety systems. These mechanisms are routinely evaluated post-testing in a static fashion but lack insights to their dynamic behavior. However, thanks to fast X-ray imaging one can assess the function of these safety mechanisms in-situ. In this work, micro batteries equipped with a combined venting and current interruption mechanism have been subjected to abuse testing in combination with synchrotron high-speed X-ray imaging. Acquired radiography reveals that the current interrupting system was not always activated as described by the manufacturer, and thus provides insights into potential improvements of the system. In addition, the cell was tested in a different configuration where this mechanism was impeded and we conclude that in-situ visualization with X-ray imaging is a crucial tool for validation of safety mechanisms integrated into batteries. • We show that synchrotron high-speed X-ray imaging is a valuable tool for in-situ evaluation of integrated safety mechanisms. • We investigated the dependence of the cell state of charge on the function of safety mechanisms and found no difference in their activation reliance. • We conducted tests on the cell in various configurations, including one where the cell was pressed between two surfaces and blocked the safety vent. In this particular configuration, we found that the cell reached higher failure temperatures, thus highlighting the importance of battery orientation in device design. • We found that the CID was not activated as expected in any of the cases. [ABSTRACT FROM AUTHOR]

The present study demonstrates experimental evidence of subsurface mesoscale damage initiation and evolution in angle-ply CFRP laminates under high strain-rate loading at low temperatures using synchrotron-based X-ray MHz radiography. A bespoke set of loading, temperature control and in-situ X-ray imaging systems were applied to simultaneously correlate high strain-rate mechanical response with observed subsurface damage in a time-resolved manner. The results demonstrate that independent of temperature, damage evolved following a specific sequence; firstly intra-ply shear cracking along the fibre direction, developing into multi-layer cracking with continued deformation, and finally culminating in inter-ply delamination and complete failure of the specimen. The timescale for this sequence, however, was observed to strongly depend upon temperature, with low temperatures resulting in more rapid damage evolution and loss of mechanical strength. [ABSTRACT FROM AUTHOR]

Abstract Intentionally inducing worst-case thermal runaway scenarios in Li-ion cells on-demand is a definitive way to test the efficacy of battery systems in safely mitigating the consequences of catastrophic failure. An internal short-circuiting (ISC) device is implanted into three 18650 cell designs: one standard, one with a bottom vent, and one with a thicker casing. Through an extensive study of 228 cells, the position at which thermal runaway initiates is shown to greatly affect the tendency of cells to rupture and incur side-wall breaches at specific locations. The risks associated with each failure mechanism and position of the ISC device are quantified using a custom calorimeter that can decouple the heat from ejected and non-ejected contents. Causes of high-risk failure mechanisms, such as bursting and side-wall breaches, are elucidated using high-speed synchrotron X-ray imaging at 2000 frames per second and image-based 3D thermal runaway computational models, which together are used to construct a comprehensive description of external risks based on internal structural and thermal phenomena. [ABSTRACT FROM AUTHOR]

[Display omitted] • Local mechanical tests of Al/Cu welded joints by MPW under high strain rates. • In-situ damages measurements with X-ray radiography under synchrotron beam. • Different interface evolution of aluminum/copper samples are observed. • Visualization of cracks on the Al/Cu joints along the interface by microtomography. Magnetic Pulse Welding (MPW) is a method of growing interest allowing the joining of dissimilar materials such as aluminum and copper. The global mechanical properties of the joint are often evaluated with conventional tests, using the fully welded joint. However, these cannot elucidate the local mechanical properties of the joint or its interface when subjected to high strain rates loads. Cubic samples of Al/Cu have been designed and extracted from MPW joints, in order to locally characterize the mechanical properties. Samples were exposed to high strain-rate loading using the Split-Hopkinson Pressure Bar (SHPB) coupled to ultra-fast synchrotron X-ray radiography in order to investigate related failure processes in-situ. The measurements of the interface evolution were related to the macroscopic applied load. In addition, synchrotron microtomography was performed on the samples before mechanical deformation. Aside from the feasibility proof, this work provides, for the first time, the correlation of the interfacial opening evolution and the influence of pre-existing cracks of the weld. It is observed that, the pre-existing cracks at the interface correspond to the initiation sites of interfacial separation between the two dissimilar metals. [ABSTRACT FROM AUTHOR]

Abstract: Purpose: Attenuation-based tomosynthesis has proven to successfully resolve the glandular tissue overlap present in mammography. However, the ability of tomosynthesis to differentiate tumorous and glandular tissue remains limited, due to the small differences in X-ray attenuation in breast tissue. One possibility to overcome this limitation and to further increase the diagnostic value of tomosynthesis exams, is the application of recently developed grating-based phase-contrast methods, which provide complementary information on the phase shift and the local scattering power of the sample. In this study, we report on first phase-contrast breast tomosynthesis results of a mastectomy sample slice with an invasive ductal carcinoma. Material and methods: A slice of a mastectomy sample with histologically proven invasive ductal cancer was imaged at the synchrotron radiation source ESRF (Grenoble, France). We used a two-grating interferometer setup at the ninth fractional Talbot distance and with an X-ray energy of 23keV. In grating interferometry absorption, differential phase, and scattering images are recorded simultaneously. The tomosynthesis scan comprises 61 projections. Multimodal tomosynthesis results were reconstructed using a standard filtered back-projection approach. Our findings are supported by a comparison of tomographic views to histopathology. Results: Phase-contrast tomosynthesis combines the advantage of improved soft-tissue discrimination in phase-contrast imaging with the ability of tomosynthesis to provide a third dimension so that improved feature visibility is not hampered by superposition artifacts. Our results indicate superior diagnostic value due to the depth resolution supplied in tomosynthesis imaging; a region of necrotic tissue that is obscured in a projection image can clearly be depicted in one single tomosynthesis slice. Compared to absorption tomosynthesis alone, soft tissue contrast is significantly enhanced in phase-contrast tomosynthesis views, where fibrous structures are clearly visible. Conclusion: In this article we present the first proof-of-principle grating-based phase-contrast tomosynthesis of a mastectomy sample section. A comparison of conventional attenuation with phase-contrast and dark-field tomosynthesis indicates that complementary information from three signals yields an increase in diagnostic value, which is verified in a comparison of our results to histological sections of the sample. As grating-based phase-contrast mammography efficiently works with conventional lab sources, our benchmark results indicate the potential benefit of translating phase-contrast tomosynthesis into a clinical setting. [Copyright &y& Elsevier]