Search Results (45)

Al-based nanocomposite energetic materials have broad application prospects in explosives and propellants, owing to their excellent energy release efficiency. However, their insufficient reliability, poor stability, and difficulty of formation limit their practical application. This study employed self-assembly using a hydrophilic polymer polyvinylpyrrolidone (PVP) together with nano-aluminum powder (Al), copper oxide (CuO), and ammonium perchlorate (AP) to obtain high-strength and high-activity composite micrometer-sized microspheres. The influence of PVP concentration on the mechanical behavior of Al/AP composite microspheres was systematically investigated, and Al was replaced with ultrasonically dispersed Al/CuO to explore the mechanism of action of PVP in the system and the catalytic behavior of CuO. PVP significantly enhanced the interfacial bonding strength. The Al/AP/5%PVP microspheres achieved a strength of 8.4 MPa under 40% compressive strain, representing a 365% increase relative to Al/AP. The Al/CuO/AP/5%PVP microspheres achieved a strength of 10.2 MPa, representing a 309% increase relative to Al/CuO. The mechanical properties of the composite microspheres were improved by more than threefold, and their thermal reactivities were also higher. This study provides a new method for the controlled preparation of high-strength, high-activity, micrometer-sized energetic microspheres. These materials are expected to be applied in composite solid propellants to enhance their combustion efficiency. Full article

As CMOS technology continues to downsize to the nanometer range, the exponential growth predicted by Moore’s Law has been significantly decelerated. Doubling chip density in the two-dimensional domain will no longer be feasible without further device downsizing. Meanwhile, emerging new device technologies, which may be incompatible with the mainstream CMOS technology, offer potential performance enhancements for system integration and could be options for a More-than-Moore system. Additionally, the explosive growth of artificial intelligence (AI) demands ever-high computing power and energy-efficient computing platforms. Heterogeneous multi-chip integration, which combines diverse components or a larger number of functional blocks with different process technologies and materials into compact 3D systems, has emerged as a critical pathway to overcome the performance limitations of monolithic integrated circuits (ICs), such as limited process/material options, low yield, and multifunctional design complexity. Furthermore, it sustains Moore’s Law progression for a further smaller footprint and higher integration density, and it has become pivotal for “More-than-Moore” strategies in the next CMOS technology revolution. This approach is also crucial for sustaining computational advancements with low-power dissipation and low-latency interconnects in the coming decades. The key techniques for heterogeneous wafer-to-wafer bonding involve both copper-to-copper (Cu-Cu) and dielectric-to-dielectric bonding. This review provides a comprehensive comparison of recent advancements in Cu-Cu bonding techniques. Major issues, such as plasma treatment to activate bonding surfaces, passivation to suppress oxidation, Cu geometry, and microstructure optimization to enhance interface diffusion and regrowth, and the use of polymers as dielectrics to mitigate contamination and wafer warpage, as well as pitch size scaling, are discussed in detail. Full article

The effect of the void defect on β−HMX−based polymer−bonded explosives (PBXs) for a comprehensive understanding of the deformation and fracture process is lacking. In this paper, the atomic scale model of the β−HMX crystal and its PBX is built using LAMMPS software to investigate the mechanical response under dynamic tensile conditions. The void defect considers both regular and stochastic distributions. The simulation concerns the deformation and fracture process with respect to the void size, void number, void spacing, and the stochastic characteristics. The tensile stress–strain relationship is obtained, and the fracture morphology is simulated well. The crack propagation is discussed in detail. Further, the fracture mode is compared between the single crystal and PBX. In addition, the characteristic defect parameter combines both the damage area and the void spacing, and it is used to predict the crack occurrence and propagation for the single crystal. However, for PBX, the interface between the crystal and binder determines the fracture process instead of the characteristic defect parameter. Full article

The dynamic mechanical properties and damage behaviors of polymer-bonded explosives (PBXs), as a kind of highly particle-filled polymer composite, must be known to ensure the safe use of related weapons and munitions. The high particle volume fraction of PBXs, which can reach approximately 95%, makes it difficult to investigate their mechanical properties and damage behavior via conventional methods. In this study, a microstructural model was developed by employing the Voronoi correction method to achieve a highly particle-filled PBX. Additionally, a bilinear model was used to accurately represent the nonlinearity of the stress–strain curve, while a zero-thickness cohesive zone model was incorporated to effectively describe the damage mechanism. The dynamic mechanical properties and damage behavior of PBXs with high particle fractions were elucidated to comprehensively understand the effects of strain rate, interface strength, and particle volume fraction on peak stress, failure strain, and damage extent. The numerical results exhibit excellent concurrence with existing experimental measurements and other computational simulations. The mechanical behavior of PBXs was also described by developing a viscoelastic model based on damage, which incorporated the equations associated with macroscopic and microscopic damage evolution. Overall, the proposed numerical technique is effective for comprehending the mechanical behavior and microscopic damage response of PBXs subjected to dynamic compression. Full article

Ultrasonic imaging methods show significant advantages in detecting internal defects of composite crystalline materials. For polymer-bonded explosives (PBXs) with highly filled crystalline particles, the strong acoustic attenuation caused by their heterogeneous crystalline structure leads to low signal-to-noise ratios (SNRs) in the full matrix capture (FMC) signals and strong background noise in reconstructed images. To realize the high-SNR imaging of defects in PBXs, this paper is the first to schematically reorganize the nonlinear post-process algorithms which have the potential to realize high-SNR imaging of defects in crystalline particle-filled explosives. Six kinds of beamforming algorithms (DAS, F-DMAS, BB-DMAS, DMAS3, L-DMAS, and DS-DMAS) were applied to the same FMC data to reconstruct the images of prefabricated side-drilled holes (SDHs) in PBXs. The image quality in terms of SNR, lateral and axial resolution, and calculation efficiency was compared and evaluated quantitatively. The experimental results show that the nonlinear beamforming algorithms showed significant improvements in SNR and resolution. In particular, L-DMAS and DS-DMAS exhibited excellent imaging capability in SDH defect detection compared to the other algorithms, with effective suppression of crystalline structural noise. Full article

Heavy metal powders driven by explosions can enhance the near-field lethality of explosive warheads by forming a quasi-pressure field while reducing collateral damage at medium and long ranges. Incorporating polymers into high-content metal powders prevents powder sintering under explosive high pressure, enhancing dispersion uniformity and making them promising for controllable warhead applications. To describe the mechanical behavior of materials under impact loading, this paper investigates the dynamic and static mechanical properties and constitutive modeling of tungsten powder/polytetrafluoroethylene (PTFE) composites. Quasi-static compression tests and split Hopkinson pressure bar (SHPB) dynamic tests were conducted on composites with varying tungsten contents (0 wt%, 70 wt%, 80 wt%, and 90 wt%) and particle sizes (200 μm, 400 μm, and 600 μm), obtaining compressive stress–strain curves over a strain rate range of 0.001 to 3610 s⁻¹. The compressive strength of the composites slightly decreased with increasing tungsten particle size but increased with higher tungsten content. Under quasi-static compression, the compressive strength of the composites with 70 wt% and 80 wt% tungsten was lower than that of pure PTFE. This was due to the bonding strength between the tungsten particles and the resin being weaker than the cohesion within the resin. Additionally, the random distribution of the tungsten particles in the matrix led to shear cracks propagating along the phase interfaces, reducing the compressive strength. The compressive strength of the composites with 90 wt% tungsten exceeded that of pure PTFE, as the packed arrangement of the tungsten particles increased the material strength through particle extrusion and friction during compression. Under dynamic impact, the compressive strength of the composites was higher than that of pure PTFE, primarily due to particle extrusion and friction effects. The composites exhibited significant strain rate sensitivity, with both the compressive strength and critical strain increasing quasi-linearly with the strain rate. Based on the experimental data, a damage-modified Zhu–Wang–Tang (ZWT) viscoelastic model was employed to fit the data, effectively characterizing the uniaxial compressive constitutive behavior of tungsten powder/PTFE composites. Full article

3-nitro-1,2,4-triazol-5-one (NTO) has been widely used as a kind of insensitive single-compound explosive owing to its excellent balance between safety and explosive energy. To reduce its possible acid corrosion and extend its application to insensitive ammunition, acid protection research on NTO-based explosives is significant. Traditionally, the acid protection effect was evaluated by metal corrosion, which is time-consuming and qualitative. An efficient and quantitative method is desirable for evaluating the acid protection effect and exploring novel protection materials. Herein, a polyimide of 4,4’-(hexafluoroisopropene)diphthalic anhydride (6FDA)/2,2-bis(trifluoromethyl)-4,4-diaminobiphenyl (TFMB) was synthesized by replacing the 4,4’-diaminodiphenyl ether (ODA) monomer with a TFMB monomer to act as an acid-protective coating material for NTO-based explosives. Compared with three other coating materials, polyvinylidene fluoride (PVDF), polyetherimide (PEI), and copolyimide (P84), the fluorinated polyimide exhibits the best acid protection effect. Moreover, a new method was constructed to obtain the pH time-dependent curve in order to evaluate efficiently the acid protection effect of the polymer materials. By the virtue of molecular dynamic simulation (Materials Studio 2023), the interfacial effects of the coating materials with NTO-based explosives were obtained. The study provides an interpretation of the acid protection effect on the molecular level, suggesting that the higher content of fluorine atoms is beneficial for stabilizing the active hydrogen atom of the NTO by forming intermolecular hydrogen bonds. Full article

The accidental initiation of explosives under mechanical loads has caused numerous catastrophic events. Therefore, the dynamic damage behavior of confined polymer-bonded explosives (PBXs) must be assessed to improve their practical applicability. In this study, polymer-bonded sugar (PBS) materials were prepared using a novel agglomerate to develop a PBX substitute material with enhanced experimental safety. The mechanical properties of the PBS shell were evaluated using a dynamic compression test, which revealed that the compression response of the shell was affected by the strain rate. A low-velocity impact experiment was performed to investigate the dynamic damage and load transfer characteristics of the PBX substitute. A constitutive model was developed to characterize the mechanical response of PBS subjected to high strain rates, and implementing this model in ABAQUS ensured successful prediction of the damage evolution process associated with PBS. Simulation results indicated that the PBS specimen was primarily damaged around its center while sliding friction was dominant near the center during pressure application. Notably, different stress states result in distinct crack growth velocity histories along the axial direction, with the damage ratio progressively decreasing toward regions closer to the impact surface. Full article

A number of coating techniques have been used to improve the processability of high explosives. These techniques are typically used for developing compositions, such as boosters and fillers. The most typically used technique is the “solvent–slurry coating”. Several compositions of polymer-bonded explosives have been industrialized using this technique. The NUPC-6 polymer-bonded powder composition of hexahydro-1,3,5-trinitro-1,3,5-triazine is optimized using the solvent–slurry coating. It involved multiple processes, i.e., preparing a slurry of high explosives in an aqueous phase, dissolving the modified polymer binder in an organic solvent, maintaining both the solvent and slurry at controlled temperatures, introducing polymer binder solution and ingredients in the slurry, distilling the solvent, mixing contents homogeneously, filtering the polymer-coated hexahydro-1,3,5-trinitro-1,3,5-triazine composition, and drying in a vacuum oven. The phlegmatizing and hydrophobic agents enhance flowability and hydrophobicity. The mass flow rate, bulk density, tapped density, compressibility index, and Hausner ratio are determined to evaluate its flowability during filling operations. The results show that the composition is flowable using a filling funnel, with a 150 mm upper diameter, 25 mm flow diameter, and 136 mm total funnel height. The raw polymer binder was modified using diisooctylsebacate and SAE-10 oil. The additives in the composition enhance its flowability, and it might be used in underwater applications. Full article

Uniaxial cyclic compression tests were performed to investigate the compression deformation and damage of polymer-bonded explosive (PBX) simulant, particularly shear localization. The macroscopic mechanical behavior and mesoscale failure mechanisms of the PBX simulant were analyzed by optical observation and SEM scanning methods. After each cyclic compression, the specimen was scanned by X-ray computed tomography (CT), and the internal 3D deformation of the specimen was calculated using the digital volume correlation (DVC) method. The results show that the stress–strain curve of the PBX simulant exhibits five stages and coincides with the morphological changes on the surface of the specimen. The mesoscale failure mechanism is dominated by particle interface debonding and binder tearing, accompanied by a small amount of particle breakage. There are three bifurcation points (T₁, T₂, and T₃) in the curves of the normal and shear strain components with compression strain. It was found that these bifurcation points can reflect the full progression of the specimen from inconspicuous damage to uniformly distributed damage, shear localization, and eventual macroscopic fracture. The strain invariant I₁ can quantitatively and completely characterize the deformation and damage processes of the PBX simulant under cyclic compression. Full article

Electrostatic accumulation is associated with almost all powder-conveying processes which could bring about electrostatic discharges. In most cases of industrial accidents, electrostatic discharge is proven to be the primary source of ignition and explosion. Herein, a surface modification process of polyaniline (PANI) is proposed to construct highly exothermic special powders, namely, HMX@PANI energetic composites, with low charge accumulation for improving powder electrostatic safety. Pure HMX are encapsulated within the PANI-conductive polymer layer through simple hydrogen bonding. Simulation results demonstrate that the forming process of HMX/aniline structure is a spontaneously thermodynamical process. The resultant inclusion complex exhibits excellent thermal stability, remarkable compatibility and intensive heat release. Importantly, PANI possesses superior electrostatic mobility characteristics because of the π-conjugated ligand, which can significantly reduce the accumulated charges on the surface of energetic powders. Moreover, the modified explosive has a narrower energy gap, which will improve the electron transition by reducing the energy barrier. The electrostatic accumulation test demonstrates that HMX@PANI composites possess a trace electrostatic accumulation of 34 nC/kg, which is two orders of magnitude lower than that of pure HMX (−6600 nC/kg) and might indicate a higher electrostatic safety. In conclusion, this surface modification process shows great promise for potential applications and could be extensively used in the establishment of high electrostatic safety for special powders. Full article

Binders mixed with explosives to form polymer-bonded explosives (PBXs) can reduce the sensitivity of the base explosive by improving interfacial interactions. The interface formed between the binder and matrix explosive also affects the thermal conductivity. Low thermal conductivity may result in localized heat concentration inside the PBXs, causing the detonation of the explosive. To investigate the binder–explosive interfacial interactions and thermal conductivity, PBXs with polyurethane as the binder and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/2,4,6-trinitrotoluene (CL-20/TNT) co-crystal as the matrix explosive were investigated through molecular dynamics (MD) simulations and reverse non-equilibrium molecular dynamics (rNEMD) simulation. The analysis of the pair correlation function revealed that there are hydrogen bonding interactions between Estane5703 and CL-20/TNT. The length of the trigger bonds was adopted as a theoretical criterion of sensitivity, and the effect of polymer binders on the sensibility of PBXs was correlated by analyzing the interfacial trigger bonds and internal trigger bonds of PBXs for the first time. The results indicated that the decrease in sensitivity of CL-20/TNT mainly comes from the CL-20/TNT contact with Estane5703. Therefore, the sensitivity of CL-20/TNT-based PBXs can be further reduced by increasing the contact area between CL-20/TNT and Estane5703. The thermal conductivity of PBXs composed of Estane5703 and CL-20/TNT (0 0 1), (0 1 0) and (1 0 0) crystal planes, respectively, were calculated through rNEMD simulations, and the results showed that only the addition of Estane5703 to the (1 0 0) crystal plane can improve the thermal conductivity of PBX100. Full article

In order to study the ignition process and response characteristics of cast polymer-bonded explosives (PBX) under the action of friction, HMX-based cast PBX explosives were used to carry out friction ignition experiments at a 90° swing angle and obtain the critical ignition loading pressure was 3.7 MPa. Combined with the morphology characterization results of HMX-based cast PBX, the friction temperature rise process was numerically simulated at the macro and micro scale, and the ignition characteristics were judged. The accuracy of the numerical simulation results was ensured based on the experiment. Based on the thermal–mechanical coupling algorithm, the mechanical–thermal response of HMX-based cast PBX tablet under friction was analyzed from the macro scale. The results show that the maximum temperature rise is 55 °C, and the temperature rise of the whole tablet is not enough to ignite the explosive. Based on the random circle and morphology characterization results of tablet, the mesoscopic model of HMX-based cast PBX was constructed, and the microcrack friction formed after interface debonding was introduced into the model. The temperature rise process at the micro scale shows that HMX crystal particles can be ignited at a temperature of 619 K under 4 MPa hydraulic pressure loaded by friction sensitivity instrument. The main reason for friction ignition of HMX-based cast PBX is the friction hot spot generated by microcracks formed after interface damage of the tablet mesoscopic model, and the external friction heat between cast PBX tablet and sliding column has little effect on ignition. External friction affects the ignition of HMX-based cast PBX by influencing the formation of internal cracks and the stress at microcracks. Full article

The increasingly harsher and more complex international and European environmental legislation drives the current development of “greener” energetics materials and munitions. The aerospace and defense industries rely on extensive research in the formulation and scale-up production of polymer-bonded explosives (PBX). In this context, this paper aims to present a versatile method for obtaining “green” PBX formulations based on two high explosives (hexogen (RDX) and octogen (HMX)) and acrylic acid—ethyl acrylate copolymeric binders. This study developed an innovative “eco-friendly” technology for coating the RDX and HMX crystals, allowing straightforward and safer manufacture of PBX, avoiding the use of traditional organic solvents. At the same time, these polymeric binders are soluble in water at a slightly alkaline pH and insoluble at acidic or neutral pH, thus ensuring a safer manipulation of the energetic materials during their entire life cycle and a facile recovery of the explosive in its original shape and morphology in demilitarization. The PBX formulations were characterized via specific analytical tools to evaluate the influence of their composition on the safety and performance characteristics: scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), alkaline pH solubility tests, differential thermal analysis (DTA), impact sensitivity test (BAM Fall Hammer Test), friction sensitivity test (BAM Friction Test), electrostatic sensitivity test (ESD), vacuum stability test, small scale shock reactivity test (SSRT), detonation velocity test. The “green” PBX formulations obtained through a simple and innovative coating method, based on the polymeric binders’ adjustable water solubility, demonstrated remarkable energetic performances and a facile recovery of the explosive crystals by the dissolution of the polymeric binder at pH 11 and 30 °C. Full article

To lay the foundation for environmentally friendly energetic polymer composites, GAP (glycidyl azide polymer) adhesive-based polymer films with different curing parameter R (mol ratio of hydroxyl/isocyanate) and energetic polymer composites with different RDX contents were studied. GAP/TDI (toluene diisocyanate)/GLY(glycerol) was selected as the adhesive system. The tensile strength and elongation at the break of the polymer film with R = 2.2, was 14.34 MPa and 176.86%, respectively, as observed by an AGS-J electronic universal testing machine. A relatively complete cross-linking network and high hydrogen bonding interaction were observed by LF-NMR (low-field nuclear magnetic resonance, where the cross-linking density was 11.06 × 10⁻⁴ mol/cm³) and FT-IR (fourier transform infrared spectroscopy, where the carbonyl bonding ratio was 64.84%). Forty percent RDX(hexogen) was added into the adhesive system. The tensile strength was 4.65 MPa, and the elongation at the break was 78.49%; meanwhile, the heat of the explosive was 2.87 MJ/kg, and the residue carbon rate was only 2.47%. The tensile cross-sections of energetic polymer composites were observed by SEM (Scanning electron microscopy). Full article