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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.

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

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]

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.

[Display omitted] • SLM-316L exhibit much larger sensitivity to defects on the dynamic mechanical response than the quasi-static case. • Intrinsic pore defects should be responsible for the anisotropic spallation behavior of the SLM-316L. • Dislocation slip dominates the spallation mechanism, accompanying by a small amount of twinning and martensite transition. 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 < 0.01 %, 260W-316L) exhibits superior spall strength of 3.87 GPa and negligible damage fraction of 0.03 % at peak stress of 4.8 GPa, which are 12 % higher and 92 % smaller than those of 0.18 % porosity specimen (300W-316L). For both horizontal and vertical impacts, hardly any anisotropy of spall strength is observed in 260W-316L, demonstrating the crucial role of the pore defects on the dynamical behavior. Moreover, dislocation slip dominated spallation mechanisms have been observed in the additively manufactured 316L specimens, accompanied by a small amount of deformation twinning and martensitic transitions. This comprehensive understanding of the defect-dependent spallation behavior and deformation mechanisms provides valuable insights for optimizing the dynamic mechanical properties of additively manufactured metals and alloys. [ABSTRACT FROM AUTHOR]

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.

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]

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]

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]

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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]

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]

High temperature oxidation of additively manufactured (Laser-powder bed fusion) IN939 (AM IN939) was studied at 900°C in dry air for 168 hours. AM IN939 cut parallel/perpendicular to the building direction, including conventionally manufactured (CM) IN939 were exposed to assess the influence of AM microstructure and its inherent anisotropy on oxidation properties. Microstructural anisotropy had no significant impact on oxidation properties. AM and CM IN939 exhibited nearly identical mass gains, yet local spallation was observed in the former. Further investigation involved oxidation of heat-treated AM IN939, revealing improved adhesion, possibly due to transformation of fine dendritic/cellular structure into coarse equiaxed grains. • Highly similar oxidation resistance of conventional (CM) IN 939 and AM IN939 at 900°C. • Anisotropy did not significantly affect the oxidation behavior of AM IN939. • As-built AM IN939 showed local spallation while the oxide was adherent on CM IN939. • AM IN939 is heat-treated to investigate the effect of microstructure on oxidation behavior. • The heat-treatment minimized spallation and buckling of oxide scales. [ABSTRACT FROM AUTHOR]

We investigate dynamic compression and fracture of ultra-high molecular weight polyethylene (UHMWPE) with plate impact experiments, high-speed velocimetry, and postmortem X-ray computed tomography. The Hugoniot equation of state of UHMWPE up to peak shock stress of ∼ 2.0 GPa is obtained via reverse impact. Spall strength and corresponding tensile strain rates are determined via symmetric impact. With increasing impact velocity, spall strength is nearly a constant (∼ 70 MPa) up at first, and then decreases continuously as a result of competition between increasing tensile strain rate, shock heating and strain softening; the damage degree increases first and then decreases rapidly at the expense of more damage nucleation sites. The void size distributions follow a power law. The small voids are closer to spheres and voids/cracks becomes flatter as void volume increases, likely because of the rearrangement and breakage of linear polymer chains of UHMWPE. [Display omitted] • Hugoniot equation of state of UHMWP is measured up to 2 GPa. • Spall strength and tensile rate are measured for UHMWP. • Spallation damage mechanisms are discussed via analysis of voids/cracks obtained from micro-CT. [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.

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.

The dual-phase steel (martensite (M)/ferrite (F)) samples with different phase content were dynamic loaded simultaneously by one-stage light gas gun. The velocity of free surface particles was measured by Doppler pin system (DPS) during the loading experiment. The soft recovered samples were investigated with optical microscopy, nanoindentation, and EBSD techniques to study the effect of the phase content on dynamic damage evolution in dual-phase steel. The results show that the sample two (1000°C/60 min + 780°C/30 min+quenching) has a higher M area percentage (77.2%), larger M size, and smaller number of M and less M/F interfaces compared with the sample one (1000°C/60 min + 740°C/30 min+quenching, with M area percentage of 45.51%). Due to the reflection and transmission of shock wave at M/F interface, tensile stress will be generated inside M with higher shock impedance. Under the same dynamic loading conditions, the more M/F interface means the greater the probability of void nucleation inside M. Thus the sample two with less M/F interfaces has lower nucleation density and lower spallation strength. The microcrack propagation resistance increases with the increase in the area percentage of M and the size of M, which results in the lower damage evolution rate of the sample two. Meanwhile, the size of M will affect the direction of microcracks propagation. Each M with larger size in the sample two is composed of several prior austenite (A) grains, and the orientation of the martensite packets in prior A grains is very different. Therefore, the microcrack propagation in the sample two is limited to different regions, the direction of microcracks propagation is easy to be deflected. [ABSTRACT FROM AUTHOR]

This work presents the production cross-sections of Ce, Tb and Dy radionuclides produced by 300 MeV to 1.7 GeV proton-induced spallation reactions in thin tantalum targets as well as the related Thick Target production Yield (TTY) values and ratios. The motivation is to optimise the production of terbium radionuclides for medical applications and to find out at which energy the purity of the collection by mass separation would be highest. For that purpose, activation experiments were performed using the COSY synchrotron at FZ Jülich utilising the stacked-foils technique and γ spectrometry with high-purity germanium detectors. The Al-27(p,x)Na-24 reaction has been used as monitor reaction. All experimental data have been systematically compared with the existing literature.

In order to study the spallation phenomenon of titanium alloy under the shock of nanosecond laser, the Neodymium-Yttrium-Aluminum Garnet laser was used to carry out laser shock experiments on the surface of titanium alloy. By observing and measuring the surface morphology of the target material, the forming factors and the changes of the surface morphology under different parameter settings, the forming criteria of the titanium alloy were obtained. The results show that under the single variable method, the change of laser energy can affect the target shape variable, and there is a positive correlation between them. When the thickness was greater than or equal to 0.08 mm, no obvious cracks were found in the targets. Moreover, the number of impact times was the key factor for the target deformation; with the growth of impact times, the target deformation gradually became larger until the crack appeared. The larger the diameter of the spot, the more likely the target was to undergo plastic deformation. The surface of titanium alloy with a thickness of 0.08 mm appeared to rebound under specific laser shock condition. The changes in the back of the target material were observed in real time through a high-speed camera, and the plasma induced by the laser was observed in the process. This study is based on the results of previous studies to obtain the titanium alloy forming criteria, which provides a basis for the setting of laser parameters and the thickness of the target when the nanosecond laser impacts the Ti-6AL-4V target. [ABSTRACT FROM AUTHOR]

• Study on spalling fracture of ST-PVA UHTCC via numerical approach. • Developed & verified two-phase mesoscale model for ST-PVA UHTCC. • Concluded effects of fibre inclination & stress wave amplitude on spallation. • Performed sixteen incident stress waveforms for numerical spallation tests. This study presents a two-phase mesoscale numerical model to investigate the dynamic spalling fracture behaviour of hybrid fibre ultra-high toughness cementitious composites (UHTCC). The model simulated the presence of random steel fibres and ductile UHTCC independently, and accurately incorporated the fibre-matrix bond-slip relationship, with carefully considering the influence of the inclination angle of the steel fibres on the pullout behaviour. Validation of the numerical model involved a meticulous comparison between numerical outcomes and results from spallation tests, encompassing strain-time and velocity-time histories, failure modes, and locations of cracking or fracture. Subsequently, the developed model was employed to analyse the impact of fibre inclination, stress wave amplitude, and waveform (based on the impulse equivalence principle) on the dynamic spalling fracture behaviour of hybrid fibre UHTCC. Evaluation of spalling fracture performance was based on both maximum velocity and pullback velocity of resulting fragments or free surfaces. Findings revealed that fibres parallel to the stress wave propagation direction exhibited optimum performance. It was also observed that stress waveforms with rectangular and sinusoidal shapes presented the highest risk of spalling fracture, while exponentially attenuated waves were comparatively safer. Additionally, stress waveforms with either rise time or duration at maximum pressure were deemed hazardous. Further, the hybrid fibre UHTCC demonstrated multiple spalling cracking/fracture behaviours under all stress waves except rectangular ones. This comprehensive exploration provided insights for the utilization of hybrid fibre UHTCC in impact engineering. [Display omitted] [ABSTRACT FROM AUTHOR]