Expansion Of Shell Research Articles

Research on the intermediate phase of 40CrMnSiB steel shell under different heat treatments

In this study, 40CrMnSiB steel cylindrical shells were tempered at 350, 500 and 600 °C to study the effect of tempering temperature on the dynamic process of expansion and fracture of the metal shell. A mid-explosion recovery experiment for the metal cylinder under internal explosive loading was designed, and the wreckage of the casings at the intermediate phase was obtained. The effects of different tempering temperatures on the macroscopic and microscopic fracture characteristics of 40CrMnSiB steel were studied. The influence of tempering temperatures on the fracture characteristic parameters of the recovered wreckage were measured and analyzed, including the circumferential divide size, the thickness and the number of the circumferential divisions. The results show that as the tempering temperature was increased from 350 to 600 °C, at first, the degree of fragmentation and the fracture characteristic parameters of the recovered wreckage changed significantly and then became essentially consistent. Scanning electron microscopy analysis revealed flow-like structure characteristics caused by adiabatic shear on different fracture surfaces. At the detonation initiation end of the casing, fracturing was formed by tearing along the crack, which existed a distance from the initiation end and propagated along the axis direction. In contrast, the fracturing near the middle position consists of a plurality of radial shear fracture units. The amount of alloy carbide that was precipitated during the tempering process increased continuously with tempering temperature, leading to an increasing number of spherical carbide particles scattered around the fracture surface.

Growth, characterization and thermo-mechanical analysis of Al/Al2O3 core/shell nanoparticles obtained under H2 atmosphere

In this work, growth, characterization and thermo-mechanical behavior of Al/Al2O3 core/shell nanoparticles (NP) is performed. The growth was carried out by gas condensation methods using H2 as carrier gas at a pressure of 100 Pa and with a temperature of the evaporation source of 1315 °C. The prepared NP were characterized by Energy Dispersive X-ray Spectroscopy for chemical information, transmission electron microscopy for morphological study, and electron diffraction patterns for structural information. The prepared Al NP exhibit a thin Al2O3 passivating oxide shell due to the air exposure when removed from the preparation vacuum chamber. Afterwards, the growth of the Al2O3 oxide shell of the Al NP and the thermo-mechanical interaction between this growing oxide shell and its Al core was studied by performing in-situ thermal X-ray diffraction from RT up to 505 °C. Coefficients of thermal expansion of both Al core and Al2O3 oxide shell were obtained by means of X-ray strain analysis. It was found that the thickness of the Al2O3 shell increases with temperature and the thermal stress induced in the system increases linearly with temperature. Our results highlight that these NP overcome higher values of fracture toughness compared with Al2O3 NP used in micro-nano composites, thus improving their mechanical properties for nanofluid applications.

The effect of shell material and load coefficient on the expansion of shell driven by detonation

Detonation driven metal expansion and fragmentation is a complex transient nonlinear dynamic problem. The research on the influence of the materials and load coefficients on expansion driven by detonation can provide a basis for fragment velocity prediction and warhead design. The numerical simulation of detonation driving was studied, including the TNT charge with five kinds of materials and six kinds of load coefficient β values shells. The characteristics in detail which the experiment was difficult to reflect were obtained, and the influence of material properties and β value of metal shells on the fragment velocities were revealed. With the increase of the density of the material, the dissipative energy of the shock wave in the casing decreases, and the contribution of the shock wave loading to the velocity of the fragment increases. Meanwhile, the increase of the shell wall thickness and the corresponding decrease of β value lead to the increase of the internal dissipation energy of the shock wave in the casings, the decrease of the energy for the shell expansion acceleration and the decrease of the contribution to the fragment velocity.

Structure and thermal expansion of coordination shells in solid and liquid Invar alloys by molecular dynamics study

Classical molecular dynamics simulations have been performed to study the atomic structures and thermal expansion of coordination shells in solid and liquid Invar alloys. Analysis of atomic structures reveals that there is an attraction between Fe-Ni nearest pairs, and that structural order still exists in the liquid Invar alloy. Fe—Ni bonds are found to have the smallest thermal expansion in the solid Invar alloy among three types of bonds, which plays an important role in the Invar effect. We also discover that the thermal expansion coefficient will gradually get close to the macroscopic level as the coordination shell number increases in Invar alloys. It is until the 5th coordination shell in the solid state and the 4th coordination shell in the liquid state that the thermal expansions of the coordination shells can reach the macroscale value. This study further promotes the understanding of the thermal expansions from the atomic scale.

Ultrafast photoinduced dynamics of single atoms solvated inside helium nanodroplets.

Helium nanodroplets can serve as reaction containers for photoinduced time-resolved studies of cold, isolated molecular systems that are otherwise inaccessible. Recently, three different dynamical processes, triggered by photoexcitation of a single atom inside a droplet, were observed in their natural time scale: Expansion of the He solvation shell (He bubble) within 600 fs initiates a collective bubble oscillation with a ∼30 ps oscillation period, followed by dopant ejection after ∼60 ps. Here, we present a systematic investigation of these processes by combining time-resolved photoelectron and photoion spectroscopy with time-dependent He density functional theory simulations. By variation of the photoexcitation energy, we find that the full excess excitation energy, represented by the blue-shifted in-droplet excitation band, is completely transferred to the He environment during the bubble expansion. Surprisingly, we find that variation of the droplet size has only a minor influence on the ejection time, providing insight into the spatial distribution of the ground-state atoms before photoexcitation. Simulated particle trajectories after photoexcitation are in agreement with experimental observations and suggest that the majority of ground-state atoms are located at around 16 Å below the droplet surface. Bubble expansion and oscillation are purely local effects, depending only on the ultimate dopant environment. These solvation-induced dynamics will be superimposed on intramolecular dynamics of molecular systems, and a mechanistic description is fundamental for the interpretation of future experiments.

Probing the Origin of Gold Dissolution and Tunneling Across Ni2P Shell Using in situ Transmission Electron Microscopy.

Hybrid core-shell catalysts possess superior physiochemical properties that are closely related to their atomic structures. Here, we report novel diffusion phenomena in an Au-Ni2P yolk-shell structure using in situ heating transmission electron microscopy (TEM) analysis. The Au yolks can dissolve completely into and diffuse across the Ni2P shell at 500 °C, resulting in an inward volume expansion of the Ni2P shell and shrinkage of the void. The dissolved Au is subsequently segregated, forming a new crystal on the outer layer of the shell. A detailed atomic-scale resolution imaging revealed that the outward Au diffusion and aggregation occur when the Au yolks are epitaxial to the Ni2P shells. Theoretical analysis shows that the outward diffusion and deposition of Au atoms is primarily driven by the excess epitaxial strain energy.

Lorentz Factor Evolution of an Expanding Jet Shell Observed in a Gamma-Ray Burst: Case Study of GRB 160625B

Abstract The Lorentz factor of a relativistic jet and its evolution during the jet expansion are difficult to estimate, especially for the jets in gamma-ray bursts (GRBs). However, the Lorentz factor is related to the jet physics. Owing to the absorption of two-photon pair production ( ), a high-energy spectral cutoff may appear in the radiation spectrum of GRBs. We search for such high-energy cutoffs in GRB 160625B, which is one of the brightest bursts in recent years. It is found that the high-energy spectral cutoff is obvious for the first pulse in the second emission episode of GRB 160625B (i.e., ∼186–192 s after the burst first trigger), which is smooth and well-shaped. Then, we estimate the Lorentz factor and radiation location of the jet shell associated with the first pulse in the second emission episode of GRB 160625B. It is found that the radiation location increases with time. In addition, the Lorentz factor remains almost constant during the expansion of the jet shell. This reveals that the magnetization of the jet is low or intermediate in the emission region, even though the jet could still be Poynting-flux-dominated at smaller radii to avoid a bright thermal component in the emission episode.

Direct Observation of Yolk-Shell Transforming to Gold Single Atoms and Clusters with Superior Oxygen Evolution Reaction Efficiency.

Noble metal particles and atoms tend not to react with other media even at elevated temperatures due to their inert nature. Herein, we report surprising findings of Au diffusion and dissolution in a Ni2P matrix, forming single Au atoms and tiny clusters. The dynamic atomic diffusion process was directly probed by in situ heating scanning transmission electron microscopy (STEM). The Au yolks can diffuse and dissolve completely into the Ni2P shell at temperatures of 350 °C or higher, resulting in an inward volume expansion of the Ni2P shell and formation of single Au atoms and tiny Au clusters in Ni2P. The resulting structure exhibited outstandingoxygen evolution reaction (OER) efficiency that is 16-fold that of commercial IrO2. The in situ STEM finding explains its drastically improved catalytic performance after annealing, confirming Au single atoms and clusters on a Ni2P surface as active OER sites. Our finding emphasizes the role of dynamic structural changes during simple heat treatment to enhance catalysis efficiency.

Failure mechanism of Au@Co9S8 yolk-shell anode in Li-ion batteries unveiled by in-situ transmission electron microscopy

Co9S8 has been regarded as a desirable anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity. However, lithium (Li) insertion caused large volume expansion, and subsequent pulverization and capacity decay are the major challenges for its practical applications in commercial LIBs. In this work, we design an Au@Co9S8 yolk-shell nanoparticle (NP) anode and use in-situ transmission electron microscopy to study the structural, morphological, and chemical evolutions in the NPs during lithiation. Our experimental results reveal that Li insertion leads to the volume expansion of the lithiated Co9S8 shell dominantly in the outward direction, and the conversion reaction between Li and Co9S8 induces the formation of a two-phase shell with metallic Co clusters dispersed in the as-formed Li2S matrix. With corroboration of chemo-mechanical simulations, we elucidate that the lithiation-generated comparative softer phase together with the inner stiffer unlithiated Co9S8 phase contributes to the outward only deformation pattern. In addition, the insulating nature of the as-formed Li2S results in an unexpected non-reactive Au yolk during lithiation. Our findings elucidate the significance of considering the dynamical phase transformations of active materials (i.e., Co9S8) for LIBs and provide valuable insights into the rational design of new generation high-performance LIBs.

Design Parameter Changeover for a Shell and Tube Direct Expansion Evaporator after Installation on Board a Commercial Fishing Vessel

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Collapse and expansion of scalar thin-shell for a class of black holes

This paper investigates the dynamics of thin-shell in the presence of perfect fluid as well as scalar field. We formulate the equations of motion using Israel thin-shell formalism by taking the interior and exterior regions of Schwarzschild, Kerr as well as Kerr–Newmann black hole. We find numerical solutions of equations of motion and effective potential to analyze the scalar shell for collapse and expansion. It is found that the rate of collapse and expansion of scalar shell through shell’s radius depend on charge and rotation parameters. We conclude that the massive scalar shell leads to collapse of thin-shell, while massless scalar shell indicates both collapse as well as expansion.

Femtosecond solvation dynamics of indium dimers inside superfluid helium nanodroplets

Indium dimers (In2) solvated inside helium nanodroplets are studied with femtosecond photoelectron and photoion spectroscopy. The solvation dynamics triggered by photoexcitation of the In2 include expansion of the solvation shell and dopant ejection from the droplet, which both proceed more slowly than for In atoms. Oscillation of the solvation shell, in contrast, is similar to the case of In atoms. These processes are observed in combination with intrinsic dynamics of the molecule and set the time-frame for the dopant interaction with the quantum fluid environment.

Femtosecond dopant-to-solvent energy transfer inside helium nanodroplets

Photoexcitation of atoms solvated inside superfluid helium nanodroplets is investigated with femtosecond photoelectron spectroscopy. Expansion of the solvation shell within about 600 fs is observed as transient photoelectron peak shift. For larger photoexcitation energies within the blue-shifted absorption band, more energy is transferred to the He droplet and the expansion proceeds faster.

Measuring the Expansion and Age of the Nova Shell IPHASX J210204.7+471015

The parallax expansion and kinematics of a nova shell can be used to assess its age and distance, and to investigate the interaction of the ejecta with the circumstellar medium. These are key to understand the expansion and dispersal of the nova ejecta in the Galaxy. Multi-epoch images and high-dispersion spectroscopic observations of the recently discovered classical nova shell IPHASXJ210204.7+471015 around a nova-like system have been used to derive a present day expansion rate of 0.100 arcsec/yr and an expansion velocity of 285 km/s. These data are combined to obtain a distance of 600 pc to the nova. The secular expansion of the nova shell place the event sometime between 1850 and 1890, yet it seems to have been missed at that time. Despite its young age, 130-170 yrs, we found indications that the ejecta has already experienced a noticeable deceleration, indicating the interaction of this young nova shell with the surrounding medium.

Expansion and Fragmentation of a Liquid-Metal Droplet by a Short Laser Pulse

We report an experimental and numerical investigation of the fragmentation mechanisms of micrometer-sized metal droplet irradiated by ultrashort laser pulses. The results of the experiment show that the fast one-side heating of such a droplet may lead to either symmetric or asymmetric expansion followed by different fragmentation scenarios. To unveil the underlying processes leading to fragmentation we perform simulation of liquid-tin droplet expansion produced by the initial conditions similar to those in experiment using the smoothed particle hydrodynamics (SPH) method. Simulation demonstrates that a thin heated surface layer generates a ultrashort shock wave propagating from the frontal side to rear side of the droplet. Convergence of such shock wave followed by a rarefaction tale to the droplet center results in the cavitation of material inside the central region by the strong tensile stress. Reflection of the shock wave from the rear side of droplet produces another region of highly stretched material where the spallation may occur producing a thin spallation layer moving with a velocity higher than expansion of the central shell after cavitation. It is shown both experimentally and numerically that the threshold laser intensity necessary for the spallation is higher than the threshold required to induce cavitation in the central region of droplet. Thus, the regime of asymmetrical expansion is realized if the laser intensity exceeds the spallation threshold. The transverse and longitudinal expansion velocities obtained in SPH simulations of different regimes of expansion are agreed well with our experimental data.

Genesis and Impulsive Evolution of the 2017 September 10 Coronal Mass Ejection

Abstract The X8.2 event of 2017 September 10 provides unique observations to study the genesis, magnetic morphology, and impulsive dynamics of a very fast coronal mass ejection (CME). Combining GOES-16/SUVI and SDO/AIA EUV imagery, we identify a hot (T ≈ 10–15 MK) bright rim around a quickly expanding cavity, embedded inside a much larger CME shell (T ≈ 1–2 MK). The CME shell develops from a dense set of large AR loops (≳0.5R s ) and seamlessly evolves into the CME front observed in LASCO C2. The strong lateral overexpansion of the CME shell acts as a piston initiating the fast EUV wave. The hot cavity rim is demonstrated to be a manifestation of the dominantly poloidal flux and frozen-in plasma added to the rising flux rope by magnetic reconnection in the current sheet beneath. The same structure is later observed as the core of the white-light CME, challenging the traditional interpretation of the CME three-part morphology. The large amount of added magnetic flux suggested by these observations explains the extreme accelerations of the radial and lateral expansion of the CME shell and cavity, all reaching values of 5–10 km s−2. The acceleration peaks occur simultaneously with the first RHESSI 100–300 keV hard X-ray burst of the associated flare, further underlining the importance of the reconnection process for the impulsive CME evolution. Finally, the much higher radial propagation speed of the flux rope in relation to the CME shell causes a distinct deformation of the white-light CME front and shock.

Femtosecond photoexcitation dynamics inside a quantum solvent

The observation of chemical reactions on the time scale of the motion of electrons and nuclei has been made possible by lasers with ever shortened pulse lengths. Superfluid helium represents a special solvent that permits the synthesis of novel classes of molecules that have eluded dynamical studies so far. However, photoexcitation inside this quantum solvent triggers a pronounced response of the solvation shell, which is not well understood. Here, we present a mechanistic description of the solvent response to photoexcitation of indium (In) dopant atoms inside helium nanodroplets (HeN), obtained from femtosecond pump–probe spectroscopy and time-dependent density functional theory simulations. For the In–HeN system, part of the excited state electronic energy leads to expansion of the solvation shell within 600 fs, initiating a collective shell oscillation with a period of about 30 ps. These coupled electronic and nuclear dynamics will be superimposed on intrinsic photoinduced processes of molecular systems inside helium droplets.

Optical and X-ray study of V404 Cyg during its activity in the Summer 2015

Abstract. The black hole X-ray binary V404Cyg was studied during of the 2015 outburst. Optical photometry and spectroscopy were performed by using 1.5-meter Russian-Turkish telescope (RTT-150) facilities at the TUBITAK National Observatory (Antalya, Turkey). From June 22 to June 28, 2015, shell expansion velocity decreased from 650 to 400 km s–1 as measured by Hα and Hβ lines and from 450 to 330 km s–1 as measured by HeI and HeII lines. Thus, the shell expansion occurred with deceleration, where the hydrogen and helium line formation regions are at different radial distances from the center of the star. The correlation of flow variability in the optical and X-ray ranges is caused by fluctuations in the rate of accretion near a compact source where X-ray photons are generated.

Effects of heat treatments to inner liner material, thermal barrier coating, and outer shell material on lifetime of a combustion chamber

Key factors were investigated to extend the lifetime of a combustion chamber of a large thrust rocket engine. Two-dimensional finite element simulations were conducted to estimate creep damage and low cycle fatigue damage to the inner liner of a combustion chamber wall. In these simulations, the effects of difference of heat treatments to the inner liner material, heat shield by a thermal barrier coating, and thermal expansion of the outer shell on lifetime were examined. It was found that heat shield by a thermal barrier coating had the largest effect in extension of the lifetime though the effect depended on the physical characteristic of the inner liner material. Expansion or contraction of the outer liner during combustion affects the restriction of the inner liner resulting in the extension of the lifetime. By combination of these effects, the lifetime can be extended up to about a factor of 10 longer than that of a combustion chamber without any effects.

Expansion of a radially symmetric blast shell into a uniformly magnetized plasma

The expansion of a thermal pressure-driven radial blast shell into a dilute ambient plasma is examined with two-dimensional PIC simulations. The purpose is to determine if laminar shocks form in a collisionless plasma which resemble their magnetohydrodynamic counterparts. The ambient plasma is composed of electrons with the temperature of 2 keV and cool fully ionized nitrogen ions. It is permeated by a spatially uniform magnetic field. A forward shock forms between the shocked ambient medium and the pristine ambient medium, which changes from an ion acoustic one through a slow magnetosonic one to a fast magnetosonic shock with increasing shock propagation angles relative to the magnetic field. The slow magnetosonic shock that propagates obliquely to the magnetic field changes into a tangential discontinuity for a perpendicular propagation direction, which is in line with the magnetohydrodynamic model. The expulsion of the magnetic field by the expanding blast shell triggers an electron-cyclotron drift instability.