Search

Hydroxyl-terminated polybutadiene/toluene diisocyanate (HTPB/TDI) system is widely used in composite solid propellants. The migrations of plasticizers and water molecules from solid propellants and surrounding environment to the inhibitor have always been the important issues. This study focuses on the preparation, characterization and anti-migration behavior of graphene oxide (GO)/HTPB nanocomposite liner. The GO/HTPB (GH) composite liners affect the migration of small molecules through a tighter cross-linked structure and weakening function of small molecule adsorption. The anti-migration performance of the liner at different temperatures was analyzed, and the influence of the added amount of GO on the anti-migration performance and adhesion performance was also systematically studied. The overall performance of the liner is optimized when the amount of GO filler is 0.3 wt%. After adding 0.3 wt% GO, the concentration of dioctyl sebacate (DOS) migrated into the liner is decreased by 23.28%, and the concentration of water molecules is decreased by 51.89%, indicating that the introduction of GO can significantly improve the anti-migration performance of the liner. In addition, the bond strength is greatly increased from 0.25 MPa to 0.95 MPa, which meets the application requirements of the current propellant system. This research provides an important way for the preparation of structure-function synergistic anti-migration composite liners.

The shielding properties of a Cu-doped Ni–Zn polycrystalline ferrite in the frequency range 1 MHz to 1 GHz were explored. Samples of composition (Cu0.12Ni0.23Zn0.65)Fe2O4 were prepared by the traditional ceramic route. The complex relative permittivity () and permeability () of the absorber ceramics were measured, and the minimum reflection-loss , matching frequency , matching thickness and bandwidth for were calculated using the theory of the absorbing wall. Effect of the main process parameters (pressing pressure P, sintering temperature T, and sintering time t) on the electromagnetic properties and microwave-absorbing characteristics was deeply investigated. The rise of the three selected process parameters was observed to improve the sintered microstructure of the final specimens (monitored by the relative density and the average grain size G), provided that abnormal grain growth does not occurred. The increase in sintered relative density and average grain growth modifies complex permeability and permittivity in the explored frequency range, enhancing the shielding properties of the material. Se han analizado las propiedades de blindaje de una ferrita policristalina de Ni–Zn dopada con Cu en el rango de frecuencia de 1 MHz-1 GHz. Las muestras de composición (Cu0.12Ni0.23Zn0.65)Fe2O4 se prepararon por la ruta tradicional cerámica, midiendo la permitividad () y la permeabilidad () relativas complejas de las cerámicas absorbentes y se calcularon, utilizando la teoría de la pared absorbente, la pérdida por reflexión mínima , la frecuencia a la que se produce esta mínima , el espesor óptimo de pieza y el ancho de banda para . Se ha llevado a cabo una investigación rigurosa del efecto de los principales parámetros del proceso (presión de prensado P, temperatura de sinterización T y tiempo de sinterización t) sobre las propiedades electromagnéticas y los parámetros característicos de estos absorbedores, observándose que el aumento de los tres parámetros de proceso seleccionados mejoran la microestructura final de las muestras sinterizadas (monitorizadas por la densidad relativa y el tamaño medio de grano G siempre que no se produzca un crecimiento anormal del grano. El aumento de la densidad relativa y el tamaño medio de grano de las piezas sinterizadas modifican la permeabilidad y la permitividad complejas en el rango de frecuencia explorado, mejorando las propiedades de blindaje del material. This study has been supported by Ministerio de Economía y Competitividad (Spain) through grant number (MAT2016-76320-R) and by Universitat Jaume I (Spain), grant numbers (UJIB2017-48 and UJIB2020-13). Complex relative permeability and permittivity determination were carried out at the central facilities (Servei Central d’Instrumentació Científica) of the Universitat Jaume I.

Polymer bonded explosives (PBXs) have high energy density, excellent mechanical properties and better thermal stability. In this study, droplet microfluidic technology was used to successfully prepare HMX/TATB microspheres. The effects of different binder types and binder concentrations on the morphology of the microspheres were studied, and results proved that NC/GAP (1:4) provides particles a regular spherical morphology and good dispersion. Subsequently, the influence of the concentration of the dispersed phase and the flow rate of the continuous phase on the particle size distribution of the microspheres was fully studied. The microspheres had narrow particle size distribution and high spherical shape. Under optimized process conditions, HMX/TATB microspheres were prepared and compared with the physical mixtures. The X-ray diffraction, differential scanning calorimetry, flow properties, bulk density, and mechanical sensitivity of the samples were also studied. Results showed that the crystal form of the microspheres remains unchanged, and the binder maintains good compatibility with explosives. In addition, the fluidity, bulk density, real density and safety performance of the microspheres are remarkably better than the physical mixture. This study provides a new method for preparing PBX with narrow particle size distribution, high spherical shape, excellent dispersion and high bulk density.

In the present study, the unique three-dimensional graphene coated nickel (Ni/C) foam reinforced silicon carbide (Ni/C@SiC) composites were first obtained via the precursor impregnation and pyrolysis (PIP) processes. The microstructure images indicated that the SiC fillers were successfully prepared in the skeleton pores of the Ni/C foam. The influence of the PIP cycles on the microwave absorption performances was researched, and the results indicated that after the primary PIP process, Ni/C@SiC–I possessed the optimal microwave absorbing performance with a minimum reflection loss(RL) of −25.87 dB at 5.28 GHz and 5.00 mm. Besides, the RL values could be below −10.00 dB from 5.88 GHz to 7.74 GHz when the corresponding matching thickness was 3.85 mm. However, the microwave absorption properties of Ni/C@SiC-II and Ni/C@SiC-III were tremendously degraded as the PIP times increased. At last, the electromagnetic parameter, dielectric loss, attenuation constant as well as impedance matching coefficient were further investigated to analyze the absorbing mechanism, which opened a new path for the certain scientific evaluation of the absorbing materials and had extremely important to the defence technology.

In this study, using a solution casting process, thermoplastic polyurethane elastomer (TPU) composites containing different contents of lead zirconate titanate (PZT) ferroelectric particles were produced. The damping treatment of composites at high volume of fillers was investigated. SEM micrographs showed that PZT particles had a proper distribution in the PU matrix. Differential scanning calorimetry (DSC) thermograms indicates that melting enthalpy decreases by raising PZT filler content. The results of the dynamic mechanical thermal analysis (DMTA) proved that the magnitude of loss factor (tan δ) strongly depends on PZT content, and it decreased from 0.51 to 0.27 as PZT content increased. The value of E0 increases to 0.32 GPa in the composite reinforced with 50 v% of PZT. The role of PZT on the acoustic behavior of TPU was measured using the acoustic absorption coefficient (a). The results showed that as PZT content increased from 0 to 50%, the acoustic absorption coefficient reached 0.25 at 6000 Hz frequency. The composites of PZT/PU with 0–3 connectivity were poled, and the optimal poling conditions that could be applied without sample breakdown were studied. Moreover, we prepared composites containing 70 vol% PZT particles by modifying the particles. Modification of PZT particles caused a decrease in both d33 and g33 constants of the PZT/PU composites.

Through quantitative statistics and morphological characterization of ceramic fragments for ceramic composite bulletproof insert plates (CCBIPs), distribution characteristics of ceramic fragments within a specific size range were analyzed for different Armor Piercing Incendiary (API) and shot times. To quantitatively evaluate the effect of energy absorption for ceramic plates, a model of energy absorption during penetration for CCBIPs was established based on statistics of the size distribution of ceramic fragments (SDCF). Variation in the SDCF and its influence on energy absorption for CCBIPs were investigated. The results indicate that the distribution feature of ceramic fragments in the range of 0.25–2.25 mm is Gaussian distribution. Compared with Type 56 of API (56-API), ceramic fragments formed by 53-API with higher kinetic energy possess more quantity and more concentrated distribution, whose average equivalence size decreases by 6.5%, corresponding to increasing by 83.9% of estimated energy absorption. Besides, the ability of CCBIPs to resist the third shot is significantly weakened, whose estimated energy absorption decreases by 58.8% compared with the first shot. More concentrated distribution and fewer fragments are formed after the third shot, the average equivalence size of ceramic fragments increases by 6.9%, which may attribute to the micro-cracks induced by the previous two shots.

To improve the defense capability of military equipment under extreme conditions, impact-resistant and high-energy-consuming materials have to be developed. The damping characteristic of entangled porous metallic wire materials (EPMWM) for vibration isolation was previously investigated. In this paper, a study focusing on the impact-resistance of EPMWM with the consideration of ambient temperature is presented. The quasi-static and low-velocity impact mechanical behavior of EPMWM under different temperatures (25 °C–300 °C) are systematically studied. The results of the static compression test show that the damping energy dissipation of EPMWM increases with temperature while the nonlinear damping characteristics are gradually enhanced. During the impact experiments, the impact energy loss rate of EPMWM was between 65% and 85%, while the temperatures increased from 25 °C to 300 °C. Moreover, under the same drop impact conditions, the overall deformation of EPMWM decreases in the temperature range of 100 °C–200 °C. On the other hand, the impact stiffness, energy dissipation, and impact loss factor of EPMWM significantly increase with temperature. This can be attributed to an increase in temperature, which changes the thermal expansion coefficient and contact state of the internal wire helixes. Consequently, the energy dissipation mode (dry friction, air damping, and plastic deformation) of EPMWM is also altered. Therefore, the EPMWM may act as a potential candidate material for superior energy absorption applications.

In view of the difficulty of kerosene-air detonation faced by the application of rotating detonation to aviation engines, in order to improve the kerosene detonation activity, the atmospheric pressure gliding arc plasma is used to conduct secondary adjustment of the pre-combustion cracking products. The results show that the components with larger molecular weight in the pre-combustion cracking products, such as ethylene and methane, can be cracked into highly active species of hydrogen and acetylene by gliding arc plasma. With the increase of the fuel ratio of pre-combustion cracking, the plasma has a more significant effect on the adjustment of high active components. However, as the flow rate of the cracking gas treated by plasma increases, the adjustment effect is obviously reduced.

A novel recycling solution for thermoplastic composites (TPCs) was recently implemented. The processing steps comprise shredding of TPC offcuts to flakes of a few centimetres, melting and blending of the flakes in a low-shear mixer, extrusion of a molten mixed dough and subsequent compression moulding in a press. This material and process are similar to the compression moulding of long-fibre thermoplastics (LFTs) that have been in the market for decades, such as glass mat thermoplastics (GMT) or direct-LFT. However, the input material in this recycling route consists of multi-layered woven flakes, which is very different from the pellets or chopped rovings of other LFTs. Process- and material-induced heterogeneities such as fibre orientation, percolation, variation of fibre fraction, or fibre attrition may be different for this new material. The development of this recycling technology and future industrial applications require more confidence in the material and process. The objective of this study is to characterise these heterogeneities for this recycling solution, and compare them to those generated in regular LFTs. It was found that the process- and material-induced heterogeneities of the recycled TPCs are similar to other LFTs, for the aspects listed here: fibre orientation, percolation, variation of fibre fraction and fibre attrition. In comparison to GMT, the effect of the mixing step is particularly noticeable on the local variation of fibre fraction within the panels. Industrial applications of this recycling route will benefit from this similarity, as it improves the confidence in the material and process combination.

Spacesuits and spacecraft must endure high velocity impacts from micrometeoroids. This work considers the impact of 100 μm diameter projectiles into composite targets at velocities from 0.5 km/s to 2 km/s. This work begins by presenting an energy-based theoretical model relating depth of penetration (DoP) and impact force to impact velocity, characteristic time, and threshold velocity and force. Next, this work compares numerical simulations of normal impact on composites to the theoretical model. Numerical simulations are conducted with LS-DYNA and the well-known composite model, MAT-162. The numerical models consider unidirectional S2-glass fiber reinforced SC-15 epoxy composite laminates. The numerical model shows good correlation with the theoretical model. The numerical model also investigates lateral impact, parallel to the fiber direction, and oblique impact at angles from 30° to 82.5°. This work decomposes oblique impact into normal and lateral components, and compares them with normal and lateral impact results. The results show good correlation of the normal component of oblique results with the theoretical model. This numerical and theoretical study focuses on DoP, velocity, and penetration resistance force as functions of time. The theoretical model and numerical simulations are used to determine new DoP parameters: characteristic time of depth of penetration and threshold impact velocity. These models are a first step in developing the capability to predict DoP for oblique, microscale, high-speed impact on composite materials.

The design of astonishing combinations of benzoxazine resins with various fillers is nowadays of great interest for high quality products, especially in ballistic armors. The objective of this study is to investigate a new hybrid material prepared as multi-layered composite plate by hand lay-up technique. Different composites were manufactured from Kevlar fabrics reinforced polybenzoxazine, which was filled with silane treated microcrystalline cellulose (MCC Si) at various amounts in the interlayers. The developed materials were tested for their flexural, dynamic mechanical and ballistic performance. The aim was to highlight the effect of adding different amounts of MCC Si on the behavior of the different plates. Compared to the baseline, the dynamic mechanical and bending tests revealed an obvious decrease of the glass transition of 21 °C and a notable increase in storage modulus and flexural strength of about 180 %and17%, respectively, upon adding 1% MMC Si as filler. Similarly, the ballistic test exhibited an enhancement in kinetic energy absorption for which the composite supplemented with 1% MCC Si had the maximal energy absorption of 166.60 J. These results indicated that the developed panels, with interesting mechanical and ballistic features, are suitable to be employed as raw materials to produce body armor.

ZrB2–SiC–HfB2–WC coating applied by spark plasma sintering led to the ablation resistance improvement of graphite substrate. The influence of HfB2/WC ratio was investigated on the ablation resistance produced by an oxyacetylene flame. The microstructural evolutions and phase characterization were studied using scanning electron microscopy and X-ray diffraction, respectively. It is confirmed that the ablation resistance of sample with 5% WC and 2.5% HfB2 was significantly increased with minimum ablated materials and rate of 1.1% and 2.2 mg s−1 employing the results of oxyacetylene flame test. The important mechanisms of improvement of the ablation resistance were the evaporation of WO3 and SiO upon oxidation of SiC and WC in the coating.

Current study renders its focus on the investigation of functionally graded Yttria Stabilized Zirconia (YSZ) and alumina (Al2O3) thermal barrier coatings (TBC) deposited on EN steel substrates used in gun barrel through atmospheric plasma spray (APS) process. A bond coat and the top coats was made with two distinct compositions using YSZ-Al2O3 in 75:25 and 50:50 weight ratio through APS process with two carrier gas concentrations of 3 and 4 standard cubic feet per hour (scfh). Coatings were characterized with thermal testing, X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscope examination (FESEM). Surface roughness test, wear and scratch test of the uncoated and coated steel specimens was also measured. YSZ-Al2O3 coated EN36C steel possessed greater insulation performance under a carrier gas flow rate of 3 scfh compared to all other specimens. EN36C steel coated with YSZ-Al2O3 in the ratio of 75:25 has better wear and scratch resistance indicating lesser deformation compared to other materials.

High-performance ballistic fibers, such as aramid fiber and ultra-high-molecular-weight polyethylene (UHMWPE), are commonly used in anti-ballistic structures due to their low density, high tensile strength and high specific modulus. However, their low modulus in the thickness direction and insufficient shear strength limits their application in certain ballistic structure. In contrast, carbon fiber reinforced epoxy resin matrix composites (CFRP) have the characteristics of high modulus in the thickness direction and high shear resistance. However, carbon fibers are rarely used and applied for protection purposes. A hybridization with aramid fiber reinforced epoxy resin matrix composites (AFRP) and CFRP has the potential to improve the stiffness and the ballistic property of the typical ballistic fiber composites. The hybrid effects on the flexural property and ballistic performance of the hybrid CFRP/AFRP laminates were investigated. Through conducting mechanical property tests and ballistic tests, two sets of reliable simulation parameters for AFRP and CFRP were established using LS-DYNA software, respectively. The experimental results suggested that by increasing the content of CFRP that the flexural properties of hybrid CFRP/AFRP laminates were enhanced. The ballistic tests’ results and the simulation illustrated that the specific energy absorption by the perforation method of CFRP achieved 77.7% of AFRP. When CFRP was on the striking face, the shear resistance of the laminates and the resistance force to the projectiles was promoted at the initial penetration stage. The proportion of fiber tensile failures in the AFRP layers was also enhanced with the addition of CFRP during the penetration process. These improvements resulted in the ballistic performance of hybrid CFRP/AFRP laminates was better than AFRP when the CFRP content was 20 wt% and 30 wt%.

The monolithic foamed propellants with high densities were prepared by casting and two-step foaming processes. Glycidyl azide polymer (GAP) and isocyanate were used as the binder system and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW, CL-20) was employed as the energetic component. The newly designed formulation containing 60 % CL-20 produced a force constant of 1077 J/g and low flame temperature of 2817 K. Two foamed propellants with densities of 1.32 g/cm3 and 1.53 g/cm3 were fabricated by a confined foaming process and examined by closed bomb tests. The results revealed that porosity significantly affects burning performance. A size effect on combustion behaviors was observed for the foamed propellant with 5.56 % porosity, and a double-hump progressive dynamic vivacity curve was obtained. At last, the 30 mm gun test was carried out to demonstrate the interior ballistic performance, and the muzzle velocity increased by 120 m/s at the same maximum chamber pressure when monolithic propellant was added in the charge.

In the study, the two-color pyrometer technique was used to measure the transient temperature field of emulsion explosives with different contents of TiH2 powders. The experimental results showed that the introduction of TiH2 powders could significantly increase the explosion temperature and fireball duration of emulsion explosive. When emulsion explosives were ignited, the average explosion temperature of pure emulsion explosive continuously decreased while emulsion explosives added with TiH2 powders increased at first and then decreased. When the content of TiH2 powders was 6 mass%, the explosion average temperature reached its maximum value of 3095 K, increasing by 43.7% as compared with that of pure emulsion explosive. In addition, the results of air blast experiment and explosion heat test showed that the variation trends of shock wave parameters, explosion heat and theoretical explosion temperature of emulsion explosives with different contents of TiH2 powders were basically consistent with that of explosion temperature measured by the two-color pyrometer technique. In conclusion, the two-color pyrometer technique would be conducive to the formula design of emulsion explosive by understanding the explosion temperature characteristics.

This study numerically simulated and investigated the flow field characteristics of a typical dual-pulse solid rocket motor with a soft pulse separation device through thermal insulation ablation under high-temperature dual-pulse erosion. The ablation rate of ethylene -propylene-diene monomer (EPDM) insulator was measured after the experiment. Experimental results were analyzed through scanning electron microscopy and microcomputed tomography. The ablation mechanism of the EPDM insulator under the operation conditions of a dual-pulse solid rocket motor was evaluated by analyzing the results. The results reveal that the internal flow field of the motor with a soft pulse separation device is uniform. The original charred layer existing on the EPDM insulator surface in the first pulse combustor is the decisive factor affecting the final ablation rate of the dual-pulse motor during the second pulse operation, and the ablation characteristic region is easily formed with the exfoliation of the charred layer. The ablation rate difference of the insulator increases with gas velocity.

Ceramic engineers have investigated the rheology of the refractory concrete to keep the balance between the desired characteristics of castables and its flow demeanor. The rheology of refractory concrete determines their application manner and a considerable fraction of its properties are largely affected by its flowability. This article gives a brief introduction to refractory concretes. It discusses the variable determinants of castables’ rheology according to their significance and their relation to each other. The measurements of rheology were examined by conventional techniques and the mathematical models of viscosity and rheometry approaches are also used for clarification. Insights into the rheology of alumina–silica containing castables were speculated through exploring submicron and nano-sized particles. The rheology of refractory concrete can be adapted properly according to the application manner and the specified requirements.

To further explore the damage characteristics and impact response of the shaped charge to the solid rocket engine (SRE) in storage or transportation, protective armor was designed and the shelled charges model (SCM)/SRE with protective armor impacting by shaped charge tests were conducted. Air overpressures at 5 locations and axial acceleration caused by the explosion were measured, and the experimental results were compared with two air overpressure curves of propellant detonation obtained by related scholars. Afterwards, the finite element software AUTODYN was used to simulate the SCM impacted process and SRE detonation results. The penetration process and the formation cause of damage were analyzed. The detonation performance of TNT, reference propellant, and the propellant used in this experiment was compared. The axial acceleration caused by the explosion was also analyzed. By comprehensive comparison, the energy released by the detonation of this propellant is larger, and the HMX or Al particles contained in this propellant are more than the reference propellant, with a TNT equivalent of 1.168–1.196. Finally, advanced protection armor suggestions were proposed based on the theory of woven fabric rubber composite armor (WFRCA).

In this paper, the manufacturing of macro-porous tubular ceramic supports for membranes is described. The novel supports are fabricated from natural diatomite and alumina raw materials using the extrusion method. The structure was analyzed by X-ray diffraction (XRD) and mercury porosimetry techniques; the presence of possible defects was investigated by scanning electron microscopy (SEM). The permeability has been measured from water flux in standard experiments. Experimental results show that the open porosity, the average pore size (APS), the pore size distribution, the strength, and the permeability of sintered supports, have been found to depend, mainly on the concentration of alumina (Al2O3) additive. Supports prepared with the addition of 10 wt.% of alumina and sintered at 1200 °C, can be considered as the most optimized; they have a porosity ratio of about 46%, an APS is around 7.7 μm, a flexural strength value of about 28 MPa, and water permeability of around 15 m3 h−1 m−2 bar−1. Such materials could be of great interest in the supports fabrication for membrane application, for instance, water filtration.

Investigating the damage and ignition behaviors of polymer-bonded explosive (PBX) under a coupled impact and high-temperature loading condition is required for the safe use of charged PBXs. An improved combined microcrack and microvoid model (CMM) was developed for better describing the thermal effects of deformation, damage, and ignition responses of PBXs. The main features of the model under typical dynamic loadings (i.e. uniaxial tension and compression, and lateral confinement) at different initial temperature were first studied. And then the effects of temperature on impact-shear sensitivity of HMX-based PBXs were investigated. The results showed that the ignition threshold velocity of shear-crack hotspots exhibits an increase from 260 to 270 to 315–325 m/s when initial temperature increases from 301 to 348 K; and then the threshold velocity decreases to 290–300 m/s with the initial temperature continually increasing to 378 K. The predicted ignition threshold velocity level of the explosives under coupled impact and high temperature loading conditions were consistent with the experimental data.

Yttrium aluminum garnet (YAG) with cerium admixture (Ce:YAG) was plasma sprayed using two different devices – gas-stabilized plasma (GSP) torch and water-stabilized plasma (WSP) torch. Coatings on stainless steel as well as self-standing plates were produced. Besides microstructure and crystallographic characterizations, dielectric tests were performed on these coatings. They included capacitance (i.e. relative permittivity), loss tangent and volume resistivity measurements. After spraying, the YAG crystal phase was preserved without any decomposition, but an amorphous fraction was detected in the as-sprayed coatings deposited by both processes. The dielectric behavior of the coatings was influenced by imperfections like splat boundaries, pores and thin cracks. The Ce:YAG samples were successfully plasma sprayed by both spray techniques. Selected aspects of wear were measured and compared with a single-crystal. The dielectric properties are comparable with the single-crystal and highly promising, particularly the loss tangent with values so low that they were not found in any other as-sprayed ceramic coating.

High efficiency, environmental protection and sustainability have become the main theme of the development of the protection engineering, requiring that the components not only meet the basic functions, but also have chemical properties such as acid and alkali corrosion resistance and aging resistance. Polyisocyanate-oxazodone (POZD) polymer has the above characteristics, it also has the advantages of strong toughness, high strength and high elongation. The concrete slab sprayed with POZD material has excellent anti-blast performance. In order to explore the damage characteristics of POZD sprayed concrete slabs under the action of contact explosion thoroughly, the contact explosion test of POZD concrete slabs with different charges were carried out. On the basis of experimental verification, numerical simulation were used to study the influence of the thickness of the POZD on the blast resistance of the concrete slab. According to the test and numerical simulation results that as the thickness of the coating increases, the anti-blast performance of the concrete slab gradually increases, and the TNT equivalent required for critical failure is larger. Based on the above analysis, empirical expressions on normalized crater diameter, the normalized spall diameter and normalized spall diameter are obtained.

In the present study, thermal hazards of TNT and DNAN used as the molten binder in TKX-50-based melt-cast explosives were comparatively studied through accelerating rate calorimeter (ARC) and Cook-off experiments. Two kinds of ARC operation modes were performed to investigate the thermal safety performance under adiabatic conditions (HWS mode) and constant heating (CHR mode). The obtained results demonstrated that at both heating modes, DNAN/TKX-50 outperformed TNT/TKX-50 from the thermal safety point of view. However, the sensitivity to heat of the samples was reverse because of the different heating modes. In addition, the results of thermal hazard assessment obtained from the cook-off experiment complied with ARC analysis which indicated the molten binder TNT replaced by DNAN would reduce the hazard of the TKX-50 melt cast explosive. Furthermore, the results of cook-off experiments also showed that DNAN/TKX-50 outperformed TNT/TKX-50 from the aspect of thermal stability, which was consistent with the result of CHR mode because of the similar heating process.

The appearance of high-entropy alloys (HEAs) makes it possible for a material to possess both high strength and high ductility. It is with great potential to apply HEAs under extreme conditions such as in the penetration process. In this paper, experiments of WFeNiMo HEA and tungsten heavy alloy (WHA) projectiles penetrating medium-carbon steel were conducted by using the ballistic gun and two-stage light-gas gun that can accelerate projectiles to impact velocities ranging from 1162 m/s to 2130 m/s. Depth of penetration (DOP) at elevated impact velocities of HEA and WHA projectiles were obtained firstly. Combined with the macroscopic and microscopic analysis of the residual projectiles, the transition of the penetration mode of the WFeNiMo HEA projectile was identified systemically. The experimental results indicated that the penetration mode of the HEA projectile changes from self-sharpening to mushrooming with the increase of impact velocity, while for the WHA projectile, the penetration mode is always mushrooming. The microstructure of the residual HEA projectiles showed that the phases tangle with each other and the morphology of the microstructure of the phases differs in the two penetration modes. Besides, the evolution of shear bands and fractures varies in the two modes. The evolution of the microstructure of HEAs causes the sharp-pointed nose to disappear and the HEA projectile ultimately becomes blunt as the impact velocity increases.

YAG (Y3Al5O12) transparent ceramics have attractive application prospects for transparent armor protection modules because of their excellent light transmittance and anti-ballistic capability. Understanding the fracture behavior and damage mechanism of YAG is necessary for armor design. To explore the damage characteristics of YAG under compression and tension, shock compression and shockless spalling experiments with soft recovery technique are conducted. The spall strength of YAG is obtained and the recovered samples are observed by CT and SEM. It is shown that the macroscopic damage characteristic of YAG under compression is vertical split cracks with oblique fine cracks distributed in the entire sample, while that under tension is horizontal transgranular cracks concentrated near the main spall surface. The cracks generated by macroscopic compression, tension and shear stress extend in similar tensile form at the microscale. The proportion of transgranular fractures on spall surfaces is higher than that of cracks induced by macroscopic compression. Meanwhile, higher loading rate and longer loading duration increase the transgranular fracture percentage.

Thin-walled lattice materials can be applied as energy absorbers in protective structures of civil defense. In this paper, quasi-static in-plane crushing tests were carried out to investigate the crushing behavior and energy absorption of buckling induced meta-lattice structures (BIMSs) with different central angles made of plastic iron material DT3 and formed by wire cutting technique. Three crushing patterns were revealed and analyzed. The test results clearly show that the initial peak force (IPF), the crushing force efficiency (CFE), the specific energy absorption (SEA) and the mean crushing force (MCF) can be substantially improved by introducing buckling pattern into the straight-walled lattice structure. The MCF of the BIMS was consistently predicted based on the simplified super folding element (SSFE) and the flattening element.

The booming development of DIW technology present an unprecedented prospect in energetic materials field and has attracted great interest due to its relative simplicity and high flexibility of manufacturing. Herein, a novel CL-20 based explosive ink formulation have been developed successfully for MEMS initiation systems via DIW technology. We designed PVA/GAP into an oil-in-water(O/W)emulsion, in the way that the aqueous solution of PVA as water phase, the ethyl acetate solution of GAP as oil phase, the combination of Tween 80 and SDS as emulsifier, BPS as a curing agent of GAP. The ideal formulation with good shear-thinning rheology properties and clear gel point was prepared using only 10 wt% emulsion. The dual-cured network formed during the curing process made the printed sample have good mechanical properties. The printed samples had satisfactory molding effect without cracks or fractures, the crystal form of CL-20 not changed and the thermal stability have improved. Deposition of explosive inks via DIW in micro-scale grooves had excellent detonation performances, which critical detonation size was 1 × 0.045 mm, detonation velocity was 7129 m/s and when the corner reaching 150° can still detonated stably. This study may open new avenues for developing binder systems in explosive ink formulations.

Since the multi-layered structures are widely used nowadays, and due to interesting applications of cylindrical shells, this study is dedicated to analyzing free vibrational behaviors of functionally graded saturated porous micro cylindrical shells with two nanocomposite skins. Based on Biot's assumptions, constitutive relations for the core are presented and effective properties of the skins are determined via the rule of mixture. A sinusoidal theory is used to capture the shear deformation effects, and to account for the scale effects, the modified couple stress theory is employed which suggests a material length-scale parameter for predicting the results in small-dimension. With the aid of extended form of Hamilton's principle for dynamic systems, differential equations of motion are extracted. Fourier series functions are used to obtain natural frequencies and after validating them, a set of parametric studies are carried out. The results show the significant effects of porosity and Skempton coefficient, pores placement patterns, CNTs addition and distribution patterns, temperature variations, material length-scale parameter and viscoelastic medium on the natural frequencies of the microstructure. The outcomes of this work could be used to design and manufacture more reliable micro cylindrical structures in thermo-dynamical environments.

A facile and economical approach was developed for the large-scale production of powdered core-shell structured PTFE/Al (CS-PA) energetic materials through ultrasonic-assisted mixing. The low-cost micrometer-sized PTFE and Al particles were used as starting materials. Under high-power ultrasonic waves, the PTFE powder was dispersed into nano-to sub-micrometer-sized particles and then encapsulated the Al microparticles to form the core-shell structure. The heat of combustion, burning rate, and pressurization rate of the powdered CS-PA were measured. The thermal-initiated reaction behavior was further evaluated using thermogravimetry-differential scanning calorimetry. Subsequently, the bulk CS-PA with a uniform microstructure was obtained via cold isostatic pressing of the powdered CS-PA followed by vacuum sintering. For the bulk CS-PA, the quasi-static compression behavior was characterized, and the impact-initiated reaction processes were conducted using the Split Hopkinson Pressure Bar (SHPB) and evaluated by a high-speed camera. Compared to physically mixed PTFE/Al materials, the powdered and bulk CS-PA demonstrated enhanced thermal- and impact-initiated reaction characteristics respectively, proving the effectiveness of our approach for constructing core-shell structures.

Nowadays, the mitigation of damage to a ship caused by the underwater explosion attracts more and more attention from the modern ship designers. In this study, two kinds of scale tests were conducted to investigate the effects of polyurea coatings on the blast resistance of hulls subjected to underwater explosion. Firstly, small-scale model tests with different polyurea coatings were carried out. Results indicate that polyurea has a better blast resistance performance when coated on the front face, which can effectively reduce the maximum deflection of the steel plate by more than 20% and reduce the deformation energy by 35.7%–45.4%. Next, a full-scale ship (approximately 50 m × 9 m) under loadings produced by the detonation of 33 kg of spherical TNT charges was tested, where a part of the ship was coated with polyurea on the front face (8 mm + 24 mm) and not on the contrast area. Damage characteristics on the bottom were statistically analyzed based on a 3D scanning technology, indicating that polyurea contributes to enhancing the blast protection of the ship. However, damage results of this test were different from those of the small-scale tests. Moreover, the deformation area of the bottom with polyurea was greatly increased by 40.1% to disperse explosion energy, a conclusion that cannot be drown from the small-scale tests.

The compression behavior of the lattice-walled tubes under variable strain rates are investigated by numerical simulation, and the stress-strain relationship of the structure under quasi-static loading is theoretically analyzed. The finite element software LS-DYNA is used to simulate the structure established by the beam element, and the critical impact velocity is obtained when the structure collapses layer by layer. According to the plastic hinge theory and considering the combined action of the beam's bending moment and axial force in the structure, the stress-strain relationship of the structure under quasi-static loading is derived and compared with the experimental results. The numerical simulation results reveal that the structure of the single-layer gradient tube(SGC) does not undergo shear deformation under quasi-static and low-speed impact. The critical speed of the gradient square tube(GS) is higher than that of a cylindrical tube. The theoretical model can correctly reflect the mechanical response of the structure under uniaxial compression.

Particle size and content of RDX are the two main factors that affect the burning stability of RDX-based propellants. However, these effects and the corresponding mechanisms are still controversial. In this work, we investigated the physicochemical processes during burning and the corresponding mechanisms through the technologies of structure compactness analysis on the base of voidage measurement and theoretical interfacial area estimation, apparent burning rate measurement using closed vessel (CV) and extinguished burning surface characterization relying on interrupted closed vessel (ICV) and scanning electron microscope (SEM). The results indicate that the voidage increased with the increase of RDX content and particle size due to the increasing interfacial area and increasing interface gap size, respectively. The apparent burning rate increased with the increase of RDX particle size because of the decreasing RDX specific surface area on the burning surface, which could decrease the heat absorbing rates of the melting and evaporation processes of RDX in the condensed phase. Similarly, the apparent burning rate decreased with the increase of RDX content at pressures lower than around 55 MPa due to the increasing RDX specific surface area. Whereas, an opposite trend could be observed at pressures higher than around 55 MPa, which was attributed to the increasing heat feedback from the gas phase as the result of the increasing propellant energy. For propellants containing very coarse RDX particles, such as 97.8 and 199.4 μm average size, the apparent burning rate increased stably with a flat extinguished surface at pressures lower than around 30 MPa, while increased sharply above around 30 MPa with the extinguished surface becoming more and more rugged as the pressure increased. In addition, the turning degree of u-p curve increased with the increase of coarse RDX content and particle size, and could be reduced by improving the structure compactness.

This article addresses the response of GLAss fiber REinforced aluminum to hypervelocity impacts of micrometeoroid analogs at impact velocities of 7 km/s and beyond. In relation, the damage modes of different GLAss fiber REinforced aluminum configurations have been exemplified. The GLAss fiber REinforced aluminum configurations comprised six to twelve variably thick aluminum layers and up to four plies of glass fiber reinforced epoxy per composite laminate. Hypervelocity impact experiments have been conducted with the help of a two-stage light-gas gun, wherein aluminum- and stainless steel projectiles were launched at velocities up to 7.15 km/s. Visual inspection of the damage area suggested the dissipation of impact energy in elastic-plastic deformation, petalling, delamination, debonding, tensile failure of fibers, and pyrolysis of epoxy. A prevailing damage mode was not apparent albeit. The quasi-isotropic ply orientation of S2-glass/FM94-epoxy laminates promoted the interference of shock- and rarefaction waves and suppressed the damage area of GLAss fiber REinforced aluminum. To discriminate between the impact performance of different GLAss fiber REinforced aluminum configurations, the energy dissipated in different damage modes of GLAss fiber REinforced aluminum has been assessed quantitatively. In terms of normalized energy, the cross-ply GLAss fiber REinforced aluminum dissipated higher energy in petal formation than in other primary damage modes. The normalized petalling energy was found to decline with the increase of impact energy. The outcomes of this study will help to optimize the GLAss fiber REinforced aluminum laminate, which will be employed as a bumper shield to prevent the fatal damage and the unzipping of a spacecraft pressure bulkhead.

Penetration and internal blast behavior of reactive liner enhanced shaped charge against concrete space were investigated through experiments and simulations. The volume of the enclosed concrete space is about 15 m3. The reactive liner enhanced shaped charge utilizes reactive copper double-layered liner, which is composed of an inner copper liner and an outer reactive liner, while the reactive material liner is fabricated by PTFE/Al (Polytetrafluoroethylene/Aluminum) powders through cold-pressing and sintering. Static explosion experiments show that, compared with the shaped charge which utilizes copper liner, the penetration cavity diameter and spalling area of concrete by the novel shaped charge were enlarged to 2 times and 4 times, respectively. Meanwhile, the following reactive material had blast effect and produced significant overpressure inside the concrete closed space. Theoretical analysis indicates concrete strength and detonation pressure of reactive material both affect the penetration cavity diameter. To the blast behavior of reactive material inside the concrete space, developing TNT equivalence model and simulated on AUTODYN-3D for analysis. Simulation results reproduced propagation process of the shock wave in concrete space, and revealed multi-peaks phenomenon of overpressure-time curves. Furthermore, the empirical relationship between the peak overpressure and relative distance for the shock wave of reactive material was proposed.

The Mg-2Zn-1.5Mn alloy (ZM21) sheets were hot-rolled in a single pass at 150 °C with different reductions through on-line heating rolling. Microstructures and edge cracking behavior of the rolled sheets were investigated. The in-situ tensile tests at 150 °C were also carried out, the crack initiation and propagation were compared with the edge cracking behavior of ZM21 sheets prepared by on-line heating rolling. The results reveal that the edge cracks are most likely to originate in the rolling direction and normal direction (RD-ND) plane due to the secondary tensile stress along RD. Edge cracking becomes more severe with an increasing reduction. The edge cracks mainly initiate and propagate in the fine recrystallized grain areas and the junction of recrystallized grains and sub-grains with hard orientation. The in-situ tensile test indicates that micro-cracks mainly initiate at the triple junction of grain boundaries where grains have hard orientation with low basal Schmid factor (SF). Meanwhile, those cracks are more likely to propagate along the grain boundaries with maximum difference in basal Schmid factor. Besides, the crack initiation and propagation during the in-situ tensile deformation at 150 °C are found not to be associated with the recrystallization.

A very coarse-grained (335 μm) Fe41Mn25Ni24Co8Cr2 high-entropy alloy with a single FCC phase was cold rolling to a 80% reduction in thickness using the differential speed rolling technique with various speed ratios (SRs) ranging between 1 and 4. As the SR was increased, the volume fraction of the region of high-density micro-shear bands increased to accommodate the higher shear strain. At SR = 4, the entire thickness of the sheet was covered with micro-shear bands, and ultrafine (sub)grains with a size of 1.4 μm were uniformly formed along the shear bands. A continuous dynamic recrystallization (CDRX) mechanism occurred during deformation, and a higher SR promoted the CDRX process. During conventional rolling (at SR=1), a brass { 110 } 〈 112 〉 orientation texture with minor components of S { 123 } 〈 634 〉 and Cu { 112 } 〈 111 〉 orientations developed. At higher SRs, shear texture developed as the main type, while the development of rolling texture was suppressed. The microstructure at SR=4 obtained after annealing at 973 K showed a fully recrystallized microstructure composed of a five times smaller grain size (4 μm) with a higher intensity of γ fiber texture compared with that prepared by conventional rolling. The annealed samples processed with high SRs exhibited superior tensile properties compared with a conventionally rolled sample in terms of strength and ductility. The current results demonstrate that by using differential speed rolling with a high SR, one can achieve a significantly finer and more homogeneous microstructure, stronger shear texture, and better tensile mechanical properties for an FCC high-entropy alloy compared to that obtained by conventional rolling. The strength of the as-rolled and annealed samples could be quantitatively explained by considering the contribution of grain size and dislocation density to strengthening.

The complex micromechanical response among grains remains a persistent challenge to understand the deformation mechanism of titanium alloys during cold rolling. Therefore, in this work, a multiscale crystal plasticity finite element method of dual-phase alloy was proposed and secondarily developed based on LS-DYNA software. Afterward, the texture evolution and slip mode of a Ti-5.5Mo-7.2Al-4.5Zr-2.6Sn-2.1Cr alloy, based on the realistic 3D microstructure, during cold rolling (20% thickness reduction) were systematically investigated. The relative activity of the 2 ¯ 0>{0001} slip system in the α phase gradually increased, and then served as the main slip mode at lower Schmid factor ( 2 ¯ 3>{10 1 ¯ 1} slip system to the overall plastic deformation was relatively limited. For the β phase, the relative activity of the {110} slip system showed an upward tendency, indicating the important role of the critical resolved shear stress relationship in the relative activity evolutions. Furthermore, the abnormally high strain of very few β grains was found, which was attributed to their severe rotations compelled by the neighboring pre-deformed α grains. The calculated pole figures, rotation axes, and compelled rotation behavior exhibited good agreement to the experimental results.

As a typical dual-phase eutectic high entropy alloy (EHEA), AlCoCrFeNi2.1 can achieve the fair matching of strength and ductility, which has attracted wide attention. However, the engineering applications of as-cast AlCoCrFeNi2.1 EHEAs still face challenges, such as coarse grain and low yield strength resulting from low solidification rate and temperature gradient. In this study, selective laser melting (SLM) was introduced into the preparation of AlCoCrFeNi2.1 EHEA to realize unique strength-ductility balance, with emphasis on investigating the effects of processing parameters on its eutectic microstructure and properties. The results show that the SLM-ed samples exhibit a completely eutectic structure consisting of ultra-fine face-centered cubic (FCC) and ordered body-centered cubic (B2) phases, and the duplex microstructure undergoes a morphological evolution from lamellar structure to cellular structure as laser energy input reducing. The SLM-ed AlCoCrFeNi2.1 EHEA presents an excellent match of high tensile strength (1271 MPa), yield strength (966 MPa), and good ductility (22.5%) at room temperature, which are significantly enhanced by the ultra-fine grains and heterogeneous structure due to rapid solidification rate and high temperature gradient during SLM. Especially, the yield strength increment of ∼50% is realized with no loss in ductility as compared with the as-cast samples with the same composition. On this basis, the precise complex component with excellent mechanical properties is well achieved. This work paves the way for the performance improvement and complex parts preparation of EHEA by microstructural design using laser additive manufacturing.

We report laser cladding of pure titanium on a CoCrMo alloy using directed energy deposition. Using electron microscopy, the microstructural evolution upon varying the process parameters, especially laser power and powder feed rate, was investigated in relation with crack formation. Cladding layers showing dilution rates of more than 5% contained cracks due to the formation of the brittle Co2Ti intermetallic phase. The observed cracks could be ascribed to a mismatch in thermal expansion and a resulting stress of more than 440 MPa acting on the Co2Ti phase, as determined by density functional theory and nanoindentation. Furthermore, an excess laser energy caused chemical inhomogeneity and unmelted Ti powder particles, while a deficient laser energy resulted in lack of fusion. Neither cracks nor partially melted powders were observed for a powder feed rate of 3 g/min and a laser power of 225-300 W, for which the dilution rate was minimized to less than 5%. For such samples the cladding layers comprised pure α-Ti and a uniform CoTi interface with Co2Ti islands.

The inverse gradient-grained CoCrFeMnNi high-entropy alloy with a desirable mechanical property that evades the strength-ductility trade-off is fabricated by the process of cold rolling and subsequent laser surface heat-treatment. Due to the gradually decayed thermal effect along with the thickness, the grain size increases from the hard core to the soft surface in terms of the inverse gradient-grained sample, which is in good consistent with the microhardness profiles. The hetero-deformation induced strengthening and strain hardening which caused by the inverse gradient-grained structure improve the strength-ductility combination, as well as the high-order hierarchal nanotwins due to the enhanced interaction with dislocations. For the laser surface heat-treatment technique, the strength and ductility are significantly increased by enlarging the microhardness difference and decreasing the thermal stress. Considering the high volume fraction of gradient-grained layer and a great deal of high-order hierarchal nanotwins in the central region, the laser surface heat-treatment technique is a promising way to produce the gradient-structured materials without thickness limitation.

In this work, the microstructure of titania coating fabricated on the surface of hydrostatically extruded titanium grade 4 with the use of the micro-arc oxidation method was studied. The surface topography and microstructure investigations performed with atomic force microscopy and scanning and transmission electron microscopy revealed that, by using an Na2HPO4 electrolyte, a well-adherent porous coating is produced on the top surface and side walls of the extruded rod. The distribution of chemical elements was analyzed by using energy dispersive X-ray spectroscopy. The chemical elements dissolved in the electrolyte i.e. (Na, P and O) incorporated into the coating. Sodium locates preferentially in the outer part of the coating, while phosphorus and oxygen are distributed throughout the whole coating. The most relevant finding shows that a grain refinement caused by a hydrostatic extrusion provoked an increase in density of high-angle grain boundaries (HAGB), which in turn secured the formation of a continuous amorphous layer close to the substrate. The presence of this layer compensates for the effect of anisotropic substrate, producing a comparable and homogenous microstructure with a large number of micropores.

s This paper investigates the effect of porosity on active damping of geometrically nonlinear vibrations (GNLV) of the magneto-electro-elastic (MEE) functionally graded (FG) plates incorporated with active treatment constricted layer damping (ATCLD) patches. The perpendicularly/slanted reinforced 1–3 piezoelectric composite (1–3 PZC) constricting layer. The constricted viscoelastic layer of the ATCLD is modeled in the time-domain using Golla-Hughes-McTavish (GHM) technique. Different types of porosity distribution in the porous magneto-electro-elastic functionally graded PMEE-FG plate graded in the thickness direction. Considering the coupling effects among elasticity, electrical, and magnetic fields, a three-dimensional finite element (FE) model for the smart PMEE-FG plate is obtained by incorporating the theory of layer-wise shear deformation. The geometric nonlinearity adopts the von Karman principle. The study presents the effects of a variant of a power-law index, porosity index, the material gradation, three types of porosity distribution, boundary conditions, and the piezoelectric fiber's orientation angle on the control of GNLV of the PMEE-FG plates. The results reveal that the FG substrate layers' porosity significantly impacts the nonlinear behavior and damping performance of the PMEE-FG plates.

High velocity ballistic impact deformation behaviour of Titanium/GFRP Fiber Metal Laminates (FML) has been explored. Both single and multiple projectiles impact conditions were considered. Ti/GFRP FML targets were fabricated with addition of 5% and 10% weight percentage of boron carbide (B4C) particles. Mechanical properties of Ti/GFRP FML targets were determined as per ASTM standards. High velocity ballistic experiments were conducted using Armour Piercing Projectile (APP) of diameter 7.62 mm and velocity ranging between 350 and 450 m/s. Depth of penetration of the projectile into the target was measured. The deformation behaviour of Ti/GFRP targets with and without the presence of ceramic powder (B4C) was investigated. “Ductile hole growth” failure mode was observed for pure GFRP target when subjected to single projectile impact whereas “plugging” failure mode was noted for Ti/GFRP targets. The presence of B4C (5% by weight) particles has significantly improved the ballistic resistance of the Ti/GFRP FML target by offering frictional resistance to the projectile penetration. Further addition (10% by weight) of B4C has reduced the ballistic performance due to agglomeration. None of the targets showed ‘brittle cracking’ or ‘fragmentation’ failures. When compared to the published results of Aluminium (Al 1100/GFRP and Al 6061/GFRP) FMLs, Ti/GFRP FML showed lesser DoP which increases its potential application to aerospace industry.

Ballistic impact response of resistance-spot-welded (RSW) double-layered (2 × 1.6 mm) plates (190 mm × 150 mm) for Q&P980 steel impacted by a round-nosed steel bullet (12 mm diameter and 30 mm length) was investigated by using gas gun and high-speed camera system. The RSW specimens were spot welded using a 6 mm diameter electrode face producing a 7.2 mm diameter fusion zone of the spot weld. The ballistic curve and energy balance for the tests of the spot weld of the RSW specimens at different velocity were analyzed to characterize the ballistic behavior of the RSW specimens under bullet impact. The fracture mechanisms of the RSW specimens under bullet impact were presented. For the tests below the ballistic limit, the cracks initiated from the notch-tip and propagated along the faying surface or obliquely through the thickness depending on the impact velocity. For the tests above the ballistic limit, the plug fracture in the front plate of the RSW specimen could be caused by the thinning-induced necking in the BM near the HAZ, while the plug fracture in the rear plate of the RSW specimens may be consist of the circumferential cracking from the rear surface and the bending fracture of the hinged part of material. The effects of the electrode indentation and the weld interfaces on deformation and fracture of the RSW specimens under bullet impact were revealed. For the tests above the ballistic limit, the circumferential fracture from the rear surface of the RSW specimens was always initiated along the interior periphery of the electrode indentation and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface. When the circumferential crack also formed outside the electrode indentation, the fracture on the BM/HAZ interface could be found. On the front plate of the RSW specimens, the shear/bending induced cracking from the notch-tip were observed and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface.

A great challenge hindering the use of cellulose nanofibers (CNF) as a reinforcing filler in bio-based polymeric matrices are their poor chemical compatibility. This is because of the inherent hydrophilic nature of CNF and the hydrophobic nature of the polymeric matrix. In this study, cellulose laminates were prepared by using CNF as a filler and cellulose acetate butyrate (CAB) as the polymer matrix. To improve the compatibility between CAB and CNF, the residual hydroxyl groups of CAB and the hydroxyl groups on the surface of CNF were cross-linked with bio-derived polyisocyanurate D376N (STABiO™). The composite material was obtained in one step by sandwiching a CNF sheet (10 wt%) coated with a cross-linking agent between CAB films (90 wt%) using hot pressing. When 14.3 wt% of the cross-linking agent to the total weight of CNF and CAB was added, the tensile strength and flexural strength were improved by 72.4% and 16.3%, respectively, compared with neat CAB. It was concluded that this increase in strength is a result of both: cross-linking between the CNF sheets as well as the cross-linking occurring at the CNF/CAB interface.

Sesquioxides such as Y2O3 and Sc2O3 are important optical materials, but the fabrication of their transparent ceramics remains a challenge due to the ultra-high melting point of over 2400 oC. In this work, a series of (Y1-xScx)2O3 transparent ceramics were successfully fabricated by a simple vacuum sintering process without any sintering additives, and the effect of Scandium (Sc) content on the crystal structure and optical/thermal/mechanical properties were evaluated. Y2O3 and Sc2O3 form a complete solid solution with a cubic bixbyite structure. The formation of (Y1-xScx)2O3 solid solution promotes the densification of ceramics, leading to the realization of high transparency close to the theoretical transmittance over a wide wavelength range of 0.35-8 mm. In particular, the in-line transmittance in the range of 0.6-6 mm remains above 80% for (Y1-xScx)2O3 with x = 0.23-0.31, while the pristine Y2O3 and Sc2O3 are opaque. Moreover, the mechanical properties including Vickers hardness (Hv), fracture toughness (KIC), and biaxial strength (δb) are evidently enhanced due to the solid solution strengthening, while the thermal conductivity is reduced due to the reduction of photon free path. This study demonstrates that forming of solid solution is a facile and universal approach for preparing sesquioxides transparent ceramics with high optical and mechanical quality.

The thermal stability and mechanical properties of a gradient-nanograined structure (GNS) CoCrNi medium entropy alloy (MEA) processed by ultrasonic surface rolling were studied by using isothermal/isochronal annealing tests combined with quasi-in-situ electron backscatter diffraction (EBSD) characterization and Vickers micro-hardness (HV) measurements. A layer by layer high-throughput investigation method was used to quantitatively study the grain growth kinetics and grain boundary evolution with different initial grain sizes, which could effectively save specimen and time costs. The grain nucleation and growth, as well as shrink and disappearance process through Σ3 coincidence site lattice boundary migration with slightly lattice rotation during annealing were directly revealed. The layer by layer grain growth kinetics and calculated activation energy indicate that the thermal stability of nano-grained top surface layer is relatively higher than that of nano-twined subsurface layer for the gradient CoCrNi MEA processed by ultrasonic surface rolling. Further analysis show that the grain boundary relaxation and dynamic recrystallization of the topmost nano-grains led to the decrease of grain boundary energy, thus improving their thermal stability. The present work provided theoretical basis for the application of CoCrNi MEA at high temperatures. Moreover, the high-throughput method on the investigation of grain stability by using gradient structure can be easily extended to other materials and it is of great significance for understanding the microstructural evolution of gradient materials.