Search

In response to the unclear mechanism of coal and gas outburst, the mechanical action mechanism of gas seepage on coal body damage and coal and gas outburst in working face was studied.The concept of gas permeability as a cohesive force is introduced from the perspectives of coal seepage test and soil mechanics. The mechanical form of gas pressure gradient acting on coal is clarified. Based on elasticity and plasticity mechanics, the limit equilibrium equation of coal body in working face under the action of gas pressure is constructed, and then the seepage flow is coupled with the coal body stress in the limit equilibrium area. The mechanical reasons for the generation of tensile stress and tensile failure of coal under the action of gas pressure are obtained. From the perspective of permeability effect, the failure characteristics of the spalling in the protruding cavity wall and the distribution law of the spalling body are explained, revealing the mechanical nature of gas pressure in outburst coal seam failure. The results show that the permeability force of gas bearing coal body generated by gas flow is equal to the gas pressure gradient. From the energy point of view, the seepage force reflects the gas pressure energy loss per unit length. Permeability and surrounding rock supporting pressure act together on the coal body of the working face，which becomes an important inducement to destroy the coal body. The gas flow before outburst produces extremely high permeability in the coal wall of the newly exposed working face. The seepage force does not act uniformly in the coal wall, but concentrated in the thin layer less than 0.1 m near the exposed face of the coal wall. This action feature of seepage force makes the stress in the mining direction of coal body sharply reduce or even become negative to form tensile stress, which leads to the tensile failure and instability of the thin layer and the formation of spall. Permeability and stress in coal body change significantly with time. When the coal wall is just exposed, the seepage force is more than 6 times that of the stable seepage, and the corresponding maximum tensile stress is more than 5 times that of the stable seepage. With the increase of the exposure time of the coal wall and the progress of seepage, the seepage force is continuously reduced, the tensile stress is also gradually reduced, and the layered fracture body is gradually thickened. In this process, the strength of coal seams shows a trade-off relationship with the tensile stress on the coal body. The lower the coal seam strength, the greater the tensile stress generated, the more the tensile damage of gas pressure is brought into full play, which is characterized by gas dominated outburst and typical spall failure.

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Purpose: High-energy heavy ions generated by accelerators utilized in industrial and medical uses. Ar, C, and He heavy ions have been used in the treatment of cancer. In this research, it was tried to calculate the radioactive elements production in healthy tissues around tumors by heavy ions spallation process in the direct usage of highenergy ions for the treatment of cancerous tumors. Materials and Methods: The radioactive elements production in body tissues irradiated with heavy ions was calculated by Monte Carlo N Particle X-version (MCNPX) code based on the Monte Carlo method. The F8 tally card with FT8 command was utilized to derive the activation and spallation data in the range of Z1 to Z2 atomic numbers. Results: A wide range of radioactive elements was created in healthful tissues in Ne, C, Ar, and He heavy ions therapy. Results show that 10Be,14C, 26Al, 36Cl, 39Ar, 40K, 39Ar, 32Si, 22Na, and 36Cl radioactive materials were produced for high-energy heavy ions spallation in healthy soft tissue. Conclusion: The results of this research show that due to using directly high-energy ions to treat internal tumors, healthy soft tissue is activated. Also, by irradiated Ne, C, Ar, and He ions, the radioactive elements are produced with high gains and long half-lives. Therefore, in the therapy of cancerous tumors with high-energy ions, due to the production of radioactive agents, healthy tissues are at high risk. [ABSTRACT FROM AUTHOR]

This study investigates the role of geometrically necessary dislocations (GNDs) and microstructure on void nucleation and growth in wrought and additively manufactured (AM) tantalum subjected to high-strain rate loading. Multi-modal 3D data was collected using TriBeam tomography to calculate GND densities and their spatial relationship to voids. A microstructural comparison between the wrought and AM samples identified distinct void shapes and locations, with intragranular voids and more spherical voids frequently observed in the AM dataset. Results indicate that voids preferentially form at both high-angle grain boundaries and low-angle subgrain boundaries, the latter of which are frequently observed in the AM material. Through a radial distribution analysis of all voids in the datasets, significant GND localization to near-void-surface regions was observed in both samples. 3D crystal plasticity simulations were employed to extend the experimental observations, revealing higher void growth rates in [111] oriented grains when compared to [001] grains. The simulations also suggest that GNDs can be generated as part of the void growth process, with more GND accumulation for growth in a [111] grain than a [001] grain. These findings provide valuable insights into the links between nanoscale void nucleation, mesoscale void growth, and microstructural effects in dynamically loaded tantalum.

Recent research work revealed that Ni43.9Co22.4Fe8.8Al10.7Ti11.7B2.5 HEA is one of the ultra-high strength and ductile superlattice alloys. In this work, high-temperature oxidation behavior of the as-cast Ni43.9Co22.4Fe8.8Al10.7Ti11.7B2.5 alloy was investigated at 1000 ℃ up to 100 h. The oxidized samples were characterized using X-ray Diffractometer, Energy Dispersive Spectroscopy, and X-ray Photoelectron Spectroscopy. The results revealed that the initial microstructure of the alloy consists of face centered cubic (FCC) and L12 structures. High-temperature exposure resulted in the formation of Al2O3 and TiO2 scales during the initial hours of oxidation, which eventually spall-off after 25 h of exposure allowing further oxidation. The results showed that protective oxide layers such as Al2O3 and TiO2 were not present after 100 h of exposure. The external layer of the 100 h oxidized sample was composed of Fe, Co, and Ni-rich oxides which are known to have mere effective resistance against oxygen ingression. The alloy which has superior strength and ductility may be used for high temperature applications after attaining the thermally stable fine-grain microstructure by suitable thermomechanical processing / providing oxidation resistance coating / by doping with elements having superior oxidation resistance.

Mechanical properties of additively manufactured alloys are momentously affected by the fabrication defects, thus limiting their applications in extreme conditions. Here we report on a near fully dense 316L stainless steel via optimized laser processing parameters. The results reveal that the dynamic mechanical response exhibits much greater sensitivity to defects than the quasi-static one. The densest specimen (porosity

Purpose: High-energy heavy ions generated by accelerators utilized in industrial and medical uses. Ar, C, and He heavy ions have been used in the treatment of cancer. In this research, it was tried to calculate the radioactive elements production in healthy tissues around tumors by heavy ions spallation process in the direct usage of high-energy ions for the treatment of cancerous tumors. Materials and Methods: The radioactive elements production in body tissues irradiated with heavy ions was calculated by Monte Carlo N Particle X-version (MCNPX) code based on the Monte Carlo method. The F8 tally card with FT8 command was utilized to derive the activation and spallation data in the range of Z1 to Z2 atomic numbers. Results: A wide range of radioactive elements was created in healthful tissues in Ne, C, Ar, and He heavy ions therapy. Results show that 10Be,14C, 26Al, 36Cl, 39Ar, 40K, 39Ar, 32Si, 22Na, and 36Cl radioactive materials were produced for high-energy heavy ions spallation in healthy soft tissue. Conclusion: The results of this research show that due to using directly high-energy ions to treat internal tumors, healthy soft tissue is activated. Also, by irradiated Ne, C, Ar, and He ions, the radioactive elements are produced with high gains and long half-lives. Therefore, in the therapy of cancerous tumors with high-energy ions, due to the production of radioactive agents, healthy tissues are at high risk.

There is still a lack of understanding of a possible mechanical ablation mechanism and the causes of thermal degradation of thin indium tin oxide (ITO) films. A dual hyperbolic two temperature model is applied to the ultrashort pulsed laser ablation process of 100 nm indium tin oxide films. The model describes transient optical properties by taking into account the changes in the complex dielectric function due to laser excitation. The laser excitation is modelled by free electron dynamics and a nonlinear absorption coefficient for a laser pulse duration of 700 fs and a central wavelength of 1056 nm. For peak fluences F ≤ 0:35 J/cm², we find that the modeled strain exceeds the yield strain in the regions where the experimental craters show signs of mechanical ablation behavior. For larger peak fluences F > 0:35 J/cm² the model predicts lattice temperatures Tl exceeding the melting temperature Tmelt; ITO of indium tin oxide. The computed depth where Tl ≤ Tmelt;ITO agrees with the measured ablation crater depths. [ABSTRACT FROM AUTHOR]

High-energy heavy ions produced by accelerators are used in industrial and medical applications. Recently carbon ions have been used in the treatment of cancerous tumors. Heavy ions by the spallation process will activate the soft tissue components before tumors. In this research by GEANT4 toolkit and MCNPX code simulation were tried to calculate the secondary particles and radioactive elements produced in the soft tissue around tumors by the carbon ions spallation process. In the MCNPX code, the F8 tally card with the FT8 command was used to extract the activation and spallation information of secondary particles in the Z1=1 to Z2=25 atomic numbers range. It was shown that a wide range of radioactive elements was produced in healthy tissues in carbon therapy. In addition to produced secondary particles, the Be-10 and C-14 radioactive elements were produced in high-energy carbon ions in soft tissue. Also, the GEANT4 toolkit result of produced secondary particles dosimetry was shown that the secondary particles dose per carbon ion is between 1.66 to 33.54 nGy for carbon ion energy between 1140 to 5160 MeV. The tail for 3480, 4080, and 5160 MeV of carbon ion energy are 0.12, 1.01, and 11 cm respectively. The carbon ion beam divergence increases with beam energy and achieve to 33 mm for 5160 MeV carbon ion. [ABSTRACT FROM AUTHOR]

Three different chemical vapor deposition (CVD) aluminizing processes were adopted for preparing of (Ni, Pt)Al metallic coatings, whose microstructure, element content, phase constituent and gas hot corrosion performance were evaluated and comparatively analyzed. YSZ ceramic coatings were subsequently fabricated via electron beam physical vapor deposition (EB-PVD) technique on top of the optimized (Ni, Pt)Al bond coat surface, and thermal barrier coating (TBC) specimens were subjected to 1373 K long-term thermal shock. The surface of aluminized sample with a single external reaction generator is relatively compact, and no defects such as micropores and microcracks are observed. Only a large number of protruding sediments are detected at grain boundary as well as the degree of rumpling and cross-links of these sediments is more obvious. A large amount of Pt is enriched at that grain boundary, while elemental content of Al is lower at the same location. Meanwhile, such sample basically displays β-(Ni, Pt)Al phase, and only three very weak diffraction peaks belonging to ζ-PtAl2 coexist. After long-term thermal shock, the exposed region of bond coat shows two kinds of micro-morphology. The biggest distinction between them is that the composition of Pt and Al elements is evidently different. The interfacial separation of TBCs is mainly concentrated at interface between thermally grown oxide (TGO) and bonding layers, and a very small amount of TGO layer is merely adhered to bond coat surface. It demonstrates that TGO layer is densified and thickened with the extension of thermal exposure period, and then the mismatching of thermal expansion between Al2O3 and (Ni, Pt)Al bond coat occupies the dominant factor. In addition, the grain boundary ridges and undulations on bonding layer surface can also induce accumulation of the tensile stress and further accelerate degradation of the critical interlayer interface during cooling stage of thermal shock.

Both the nanoscale helium (He) bubble and grain boundaries (GBs) play important roles in the dynamic mechanical behavior of irradiated nanocrystalline materials. Using molecular dynamics simulations, we study the shock-induced deformation and spallation failure of bicrystal copper with a nanoscale He bubble. Two extreme loading directions (perpendicular or parallel to the GB plane) and various impact velocities (0.5–2.5 km/s) are considered. Our results reveal that the He bubble shows hindrance to the propagation of shock waves at lower impact velocities but will accelerate shock wave propagation at higher impact velocities due to the local compression wave generated by the collapse of the He bubble. The parallel loading direction is found to have a greater effect on He bubble deformation during shock compression. The He bubble will slightly reduce the spall strength of the material at lower impact velocities but has a limited effect on the spallation process, which is dominated by the evolution of the GB. At lower impact velocities, the mechanism of spall damage is dominated by the cleavage fracture along the GB plane for the perpendicular loading condition but dominated by the He bubble expansion and void growth for the parallel loading condition. At higher impact velocities, micro-spallation occurs for both loading conditions, and the effects of GBs and He bubbles can be ignored. [ABSTRACT FROM AUTHOR]

The energy needed to deform an elastic solid may be recovered, while in Newtonian fluids, like water and glycerol, deformation energy dissipates on timescales of the intermolecular relaxation time τM. For times considerably longer than τM the existence of shear elasticity requires long-range correlations, which challenge our understanding of the liquid state. We investigated laser- driven free surface bubbles in liquid glycerol by analyzing their expansion and bursting dynamics, in which we found a flow- dominating, rubber- like elasticity unrelated to surface tension forces. In extension to findings of a measurable liquid elasticity at even very low deformation frequencies [L. Noirez, P. Baroni, J. Mol. Struct. 972, 16--21 (2010), A. Zaccone, K. Trachenko, Proc. Natl. Acad. Sci. U.S.A. 117, 19653--19655 (2020)], that is difficult to access under increased strain, we find a robust, strain rate driven elasticity. The recovery of deformation energy allows the bursting bubble to reach Taylor--Culick velocities 20- fold higher than expected. The elasticity is persistent for microseconds, hence four orders of magnitude longer than τM. The dynamic shows that this persistence cannot originate from the far tail of a distribution of relaxation times around τM but must appear by frustrating the short molecular dissipation. The longer time should be interpreted as a relaxation of collective modes of metastable groups of molecules. With strain rates of 106 s-1, we observe a metastable glycerol shell exhibiting a rubber- like solid behavior with similar elasticity values and characteristic tolerance toward large strains, although the molecular interaction is fundamentally different. [ABSTRACT FROM AUTHOR]

The present study aimed to provide new insights into the behavior of high-strength low-alloy steel under dynamic compression and to promote its use in high-stress applications. The dynamic compression response of a Cr-Ni-Mo-V steel under shock stresses ranging from 3.54 GPa to 19.76 GPa was investigated using loading technology. The free surface velocity of the specimen was measured using a displacement interferometer system with the range of 166–945 m/s. The Hugoniot elastic limit (HEL), spalling fracture, and microstructure evolution of specimens under different shock stresses were determined. The results showed that an α→ε phase transition occurred in the material at an impact stress of 15.63 GPa, leading to a change in particle velocity. The relationship between the shock wave velocity and particle velocity was found to be linear. The HEL of the steel was found to be consistent at 2.28 GPa, while the spall strength showed a more complex relationship with the increasing shock stress. Initially, the spall strength increased and then decreased with increasing shock stress before increasing again after the phase transformation. The fracture mode of the steel shifted from brittle fracture to ductile fracture with the increasing impact stresses, which is related to the previous plastic deformation under different impact loads. [ABSTRACT FROM AUTHOR]

Material degradation is one of the main problems in various high-temperature processes, directly resulting in the failure of the material. Crack and protective oxide film spallation caused either by mechanical stress development in the oxidation process or thermal stress due to a mismatch of the thermal expansions of the formed oxide and alloy are common forms of failure in high-temperature processes. Typically, the Pilling-Bedworth ratio (PBR) is employed to predict crack and spallation of the oxide by determining the volume changes of oxide and alloy because of its simplicity. However, this approach provides poor crack and spallation predictions. Hence, machine learning was adopted in the present work to predict oxide formation and spallation in the temperature range of 600-1,200 °C. The inputs for the present developed model were alloy compositions, oxide formed during oxidation, and oxidation conditions and periods. Furthermore, the predicted results of the present developed machine learning model were compared to those obtained by the PBR method. The present results revealed that the accuracy of the oxide spallation prediction of the present model was better than that of the PBR method. The random forest with 15 estimators was the best machine learning model. Finally, it can be concluded that the machine learning model is essential for accurate material failure prediction., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

Laser shock loading is a more promising technology for investigating spallation damage in materials under shock-wave loading. In this paper, shock-induced spallation in a 90W–Ni–Fe alloy at an ultrahigh tensile strain rate of 106 s−1 is investigated using a superintense ultrafast laser facility. The spallation of the 90W–Ni–Fe alloy was dominated by a transgranular fracture of tungsten(W) particles with a high spall strength of 6.46 GPa. Here, we found an interesting phenomenon that the formation of nanograins inside W particles leads to a new mode of transcrystalline fracture of W particles during the laser shock loading. Futhermore, most voids were nucleated inside the W particles rather than at the W/γ-(Ni, Fe) matrix-phase interface. This result contradicts the fracture theory under quasi-static loading, which posits that the W/γ-(Ni, Fe) matrix-phase interface is not the preferred site for the initial failure under shock loading.

In this work, the high-temperature corrosion behaviour of pure Ni3Al (P–Ni3Al) and alloyed (2.99 wt.%Ti) Ni3Al (Ti–Ni3Al) was investigated in Ar-0.2%SO2 gas at 900–1100 °C for up to 100 h. The corrosion kinetics of P–Ni3Al and Ti–Ni3Al reveal that Ti addition increased the total weight gain at all temperatures by approximately 10 times than without Ti (P–Ni3Al). The alloy initially gained more weight with the increase in temperature; but later on, the corrosion kinetics changed. Because of the extensive scale spallation during cooling, which causes the creation of large and deep geometric voids, the corrosion kinetics of P–Ni3Al deviated from the parabolic rate law. At all temperatures, Ti strengthened the scale adherence as it occupied the Al substitutional sites with a broad atomic radius, and facilitated the creation of ordered phases known as the gamma prime phase (γ′). Owing to the ordered structure, it was assumed that the diffusion of occupying atoms would be slower, thereby increasing the scale adherence. Darker inclusions were found in Ti–Ni3Al at the scale–matrix interface, which were rich in TiS owing to inward sulphur diffusion.

Failure and healing behavior of oxide scales for powder metallurgy superalloy with varying Nb contents (0, 0.5, 1, 2 wt%) during cyclic oxidation were studied. The cyclic oxidation test of four alloys was conducted using the discontinuous thermogravimetric method which consists of 100 cycles of 1 h exposure in air from 20 °C to 900 °C. The oxide scales after cyclic oxidation were systematically characterized by scanning electron microscope (SEM), laser scanning microscopy (LSM) etc. It has been found that the spallation of oxide scale in all alloys took place via expanding of the initiated cracks at grain boundaries into grain matrix. After spallation, the exposed alloy matrix would be re-oxidized into a Cr 2 O 3 layer to recover the failed oxide scales. The spallation tendency of oxide scale was significantly inhibited by Nb addition. This can be ascribed to the faster regeneration of Cr 2 O 3 layer in alloy with higher Nb content. • Nb addition significantly decreased the spallation of oxide scales. • The spallation in oxide scales starts in terms of cracks near grain boundaries. • The repetitive regeneration of Cr 2 O 3 of high-Nb alloy resulted in a smaller spallation area of the oxide scales. [ABSTRACT FROM AUTHOR]

• Shock response of CoCrNi-based MPEAs tuned with Fe/Mn elements was investigated. • Fe/Mn elements reduce the defect nucleation barrier and improve the plastic deformability. • Mn element significantly reduces the Hugoniot elastic limit (HEL) and spall strength. • Two modes of void nucleation induced by waveform profiles were revealed. Recent researches on concentrated solid solutions have emphasized the role of various solute interactions in determining anomalous dislocation core and plastic deformation. However, the influence path of element tuning under extreme conditions is still unclear. Here, we investigated shock-induced deformation and fracture in CoCrNi-based multi-principal element alloys (MPEAs) tuned by Fe/Mn elements using large-scale molecular dynamics simulations. It was found that Fe/Mn elements could reduce the defect nucleation barrier and improve the plastic deformability. When single-element tuning is applied, the Mn element significantly reduces the production of dislocations, favoring more phase transitions from FCC to BCC or amorphous phase. The results show that Mn significantly reduces the Hugoniot elastic limit (HEL) and spall strength, while the addition of Fe element to CoCrNiMn can alleviate this effect by reducing the degree of lattice distortion. Specially, we analyzed the relationship between void nucleation and shock wave propagation, and explained the single-negative-pressure-zone nucleation as well as complex double-negative-pressure-zone nucleation phenomena. Empirical equations for the spall strength of CoCrNi-based MPEAs adjusted by Fe/Mn elements were established. This work demonstrates a potential strategy for elemental tuning to tailor the mechanical properties of polymorphism in MPEAs. [Display omitted] [ABSTRACT FROM AUTHOR]

The formation of void damage and spalling failure in ductile metallic materials under strong impact is a well-established phenomenon. In aerospace and defense technology engineering design, understanding the spalling failure process and related mechanisms is of utmost importance. This paper develops an explicit Gurson-type phase-field model that can simulate the void evolution and spalling damage of three-dimensional ductile metallic materials under high-velocity impacts based on the study of Aldakheel et al.. The model incorporates the Gurson-type void evolution equation and the phase-field approach while taking into account the pressure-dependent bulk modulus and inertia effects. This model is used to study the main processes and mechanisms of impacted layer cracking of metals in different dimensions. Meanwhile based on the study of complex spallation cracking processes in metals in two and three dimensions, observing and proposing the formation mechanism of complex spallation cracking modes in materials due to lateral and edge (base angle) rarefied effects. • An explicit Gurson-type phase-field model is developed to simulate the void evolution and spalling process in ductile metallic materials. • The model considers the pressure-dependent bulk modulus, inertia effects, heat generation and diffusion during large plastic deformation. • The processes of different impact spallation cracking problems in 1, 2, and 3 dimensions are verified and studied. • The 2D flat plate non-parallel spallation cracking mechanism and the spallation cracking cut-off mechanism are investigated; the mechanisms of different damage regions of the 3D conical spallation cracking process are given. [ABSTRACT FROM AUTHOR]

In the paper, we study the formation of laser-induced periodic surface structures (LIPSS) on diamond-like nanocomposite (DLN) a-C:H:Si:O films during nanoscale ablation processing at low fluences—below the single-pulse graphitization and spallation thresholds—using an IR fs-laser (wavelength 1030 nm, pulse duration 320 fs, pulse repetition rate 100 kHz, scanning beam velocity 0.04–0.08 m/s). The studies are focused on microscopic analysis of the nanostructured DLN film surface at different stages of LIPSS formation and numerical modeling of surface plasmon polaritons in a thin graphitized surface layer. Important findings are concerned with (i) sub-threshold fabrication of high spatial frequency LIPSS (HSFL) and low spatial frequency LIPSS (LSFL) under negligible surface graphitization of hard DLN films, (ii) transition from the HSFL (periods of 140 ± 30 and 230 ± 40 nm) to LSFL (period of 830–900 nm) within a narrow fluence range of 0.21–0.32 J/cm2, (iii) visualization of equi-field lines by ablated nanoparticles at an initial stage of the LIPSS formation, providing proof of larger electric fields in the valleys and weaker fields at the ridges of a growing surface grating, (iv) influence of the thickness of a laser-excited glassy carbon (GC) layer on the period of surface plasmon polaritons excited in a three-layer system "air/GC layer/DLN film". [ABSTRACT FROM AUTHOR]

Bond coats in environmental barrier coatings (EBCs) prevent oxidants from penetrating the substrate, mediate the mismatch of the coefficient of thermal expansion (CTE), and improve the adhesion strength between adjacent layers. However, the development of bond coats is rarely studied systematically. In this paper, the research status of the bond coats in EBCs is introduced in detail, including the materials and deposition methods. Thus far, Si, modified‐Si, mullite, etc., have been employed as bond coats. Nevertheless, visible drawbacks of each bond coat limit their application at high‐temperatures in extreme environments. Si bond coat is easily oxidized and forms thermally grown oxides that form cracks, resulting in delamination, spallation, and failure of EBCs. In the Si–HfO2 bond coat, the optimal ratios of Si/HfO2, deposition methods, distribution of Si and HfO2, and oxidation of Si remain completely unsolved. For mullite bond coat, SiO2 suffers selective evaporation in the water vapor environment, and the ratios of the Al2O3 and SiO2 in mullite coatings restrict its service lifetime. HfSiO4 is a potential candidate acting as a next‐generation bond coat in EBCs is proposed. Furthermore, choosing reasonable deposition methods is beneficial to improve the performances of the bond coats in EBCs. [ABSTRACT FROM AUTHOR]

The effectiveness of small-bubble gas injection to mitigate cavitation-induced erosion damage and decrease strain in Spallation Neutron Source (SNS) target vessels was characterized using photography, laser-line scanning, and in-situ vessel strain measurements. Observations from early targets showed that erosion damage caused appreciable mass loss along the target vessel inner wall. Later target designs incorporated a cavitation mitigation technique called small-bubble gas injection, in which small helium gas bubbles were introduced into the flowing mercury during operation. Samples removed from target vessels after operation revealed that gas injection greatly reduced or eliminated erosion damage. Photographs of the target interiors showed areas where significant erosion damage occurred in targets that were operated without gas injection. The same areas had no observable erosion damage in targets that were operated with gas injection. Laser-line scan measurements were performed on samples from several target vessels operated with and without gas injection to measure the extent of erosion damage and quantify the effect of gas injection on erosion. In-situ strain measurements during operation showed that gas injection reduced the target vessel strain by 25%–75%. These results provide conclusive confirmation that gas injection effectively mitigated erosion damage and reduced strain in SNS target vessels during operation.

The process of crack initiation, propagation, and coalescence is the essential cause of rock failure. A three-dimensional numerical model based on microscopic damage mechanics is adopted to simulate the failure process and acoustic emissions (AEs) of a jointed rock mass containing a pre-existing hole subjected to stress waves. The numerically simulated results demonstrate that transmission energy plays an important role in the failure process of specimens. The greater the energy of joint transmission is, the greater the damage to the joint transmission area of the rock mass is. Furthermore, the joint width could significantly influence crack propagation patterns and the damage of the joint transmission area of rock specimens. Moreover, the degree of damage to the local joint transmission area of the rock mass is small but then becomes more obvious when the joint angle grows larger. In addition, the wavelength of the stress wave can also affect the failure modes of the rock when stress waves are applied. As the wavelength of the stress wave reduces, the larger the damage of the rock mass is and the smaller the effect of the joint on crack propagation is. Finally, the numerical results demonstrate that the width of the specimen has a significant effect on its dynamic failure mode and degree, showing an obvious size effect. This finding could explain the lateral growth of an existing flaw in its own plane, which is a phenomenon that has not been observed in laboratory experiments.

Shock-induced consolidations of Ni/Al nanoparticles, including the consolidation behavior, exothermic reaction, intermetallic compound formation, and spallation, were systematically investigated through molecular dynamics simulation. The simulation indicates that shock consolidation of Ni/Al particles consists of two steps. Firstly, after the spread of shock wave, the cavity is densely filled by the flow deformation of the Al particles. Then, the Ni and Al particles are tightly joined together at the atomic scale by the produced high pressure and temperature. The exothermic reaction in the compressed particles is because the Ni atoms diffuse into the Al phase. Depending on whether melting takes place or not, shock consolidation can be divided into solid-state consolidation and liquid-state consolidation. In the solid-state consolidation, Ni/Al composite can be acquired with a little exothermic reaction. However, in the liquid-state consolidation, much more heat is released and intermetallic phase is formed. The spallation in the compressed particles is mainly because of the generated high-strength tensile wave but can be avoided by reducing the initial density of the Ni/Al particles or the particle velocity. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present study aimed to provide new insights into the behavior of high-strength low-alloy steel under dynamic compression and to promote its use in high-stress applications. The dynamic compression response of a Cr-Ni-Mo-V steel under shock stresses ranging from 3.54 GPa to 19.76 GPa was investigated using loading technology. The free surface velocity of the specimen was measured using a displacement interferometer system with the range of 166–945 m/s. The Hugoniot elastic limit (HEL), spalling fracture, and microstructure evolution of specimens under different shock stresses were determined. The results showed that an α→ε phase transition occurred in the material at an impact stress of 15.63 GPa, leading to a change in particle velocity. The relationship between the shock wave velocity and particle velocity was found to be linear. The HEL of the steel was found to be consistent at 2.28 GPa, while the spall strength showed a more complex relationship with the increasing shock stress. Initially, the spall strength increased and then decreased with increasing shock stress before increasing again after the phase transformation. The fracture mode of the steel shifted from brittle fracture to ductile fracture with the increasing impact stresses, which is related to the previous plastic deformation under different impact loads.

Summary: Imaging photo-induced ultrafast dynamics of nanostructure phase transition is of great interest to the fields of laser-matter interactions and nanotechnology. However, conventional ultrafast far-field optical imaging methods cannot image nanostructures as their scattering scales as D6, with D being the diamater, leading to a vanishing signal-to-noise ratio. Here, we use ultrafast ultramicroscopy to capture the spatiotemporal evolution of surface nanostructures as they undergo melting, spallation, and re-solidification processes. Our experimental observations, combined with finite difference time domain (FDTD) simulations, show agreement with molecular dynamic simulations on ultrashort laser pulse-irradiated metallic nanoparticles and suggest the occurrence of melting of nanostructures followed by photomechanical spallation within a few picoseconds. At longer timescales, we image the re-solidification dynamics of the melted nanostructures occurring within nanoseconds. The re-solidification time for nanostructured surface occurs an order of magnitude faster than for an initially flat surface. Our study demonstrates a simple but powerful far-field optical approach for studying ultrafast dynamics of nanostructures.