墨水直写增材制造技术及其在含能材料领域的研究进展

系统介绍了墨水直写(DIW)增材制造技术及其在含能材料领域的应用,重点综述了近年来DIW技术在亚稳态分子间复合物(铝热剂、铝-氟聚物)、复杂异型火炸药装药结构(固体推进剂装药、炸药装药)及火工品药剂中的研究进展,并提出与之相关的机遇和挑战。指出DIW技术在一定程度上能够弥补传统装药技术的不足,在新型多孔/特殊结构装药和能量密度递变的火炸药装药研发与制造方面极具开发应用潜力,未来可进一步加强增材制造火炸药配方应用基础研究、光-热协同固化体系研究以及弹药壳体-装药一体化制造等方面的研究,为我国新型、高精度战略武器装备的发展提供新思路与技术途径。     

Fabrication of 3D structures via direct ink writing of kaolin/graphene oxide composite suspensions at ambient temperature

Kaolin/graphene oxide composite has been widely utilized in aero-space and architectural engineering applications due to its excellent mechanical property. Direct ink writing (DIW) is a freeform rapid prototyping technology that could be used to accurately fabricate the resulting size with complex shapes. In this study, we reported the DIW of kaolin/graphene oxide (GO) composite suspensions (KGCS) to assemble 3D structures at ambient temperature for the first time. The effects of GO on the chemical constitution and microstructure of kaolin suspensions were investigated. Rheology was characterized to ensure printability of KGCS. The addition of GO in kaolin suspensions quickened a flocculation structure, which dramatically changed their rheology properties. The DIW of 3D structures from the optimal KGCS sample maintained their initial shape without spreading. The flexural and compressive strengths of the dried optimal KGCS samples were obviously enhanced due to the improvement and reduction of the micro-defects compared from cured kaolin matrix.     

A 3D Smoothed Particle Hydrodynamics Method with Reactive Flow Model for the Simulation of ANFO

ANFO (ammonium nitrate/fuel oil) is a widely used bulk industrial explosive mixture that is considered to be highly “non‐ideal” with long reaction zones, low detonation energies, and large failure diameters. Thus, its detonation poses great challenge for accurate numerical modeling. Herein, we present a numerical model to simulate ANFO based on improved smoothed particle hydrodynamics (SPH) method, which is a mesh‐free Lagrangian method performing well in simulating situations consist of moving interface and large deformation, as happened in high‐velocity impact and explosion. The improved three‐dimensional SPH method incorporated with JWL++ model is used to simulate the detonation of ANFO. Good agreement is observed between simulation and experiment, which indicates that the proposed method performs well in prediction of behavior of ANFO.     

Direct ink writing of ceramic matrix composite structures

We present the development of an ink containing chopped fibers that is suitable for direct ink writing (DIW), enabling to obtain ceramic matrix composite (CMC) structures with complex shape. We take advantage of the unique formability opportunities provided by the use of a preceramic polymer as both polymeric binder and ceramic source. Inks suitable for the extrusion of fine filaments (<1 mm diameter) and containing a relatively high amount of fibers (>30 vol% for a nozzle diameter of 840 μm) were formulated. Despite some optimization of ink rheology still being needed, complex CMC structures with porosity of ~75% and compressive strength of ~4 MPa were successfully printed. The process is of particular interest for its ability to orient the fibers in the extrusion direction due to the shear stresses generated at the nozzle tip. This phenomenon was observed in the production of polymer matrix composites, but it is here employed for the first time for the production of ceramic matrix ones. The possibility to align high aspect ratio fillers using DIW opens the path to layer‐by‐layer design for optimizing the mechanical and microstructural properties within a printed object, and could potentially be extended to other types of fillers.     

Effect of Al/O Ratio on the Detonation Performance and Underwater Explosion of HMX‐based Aluminized Explosives

The performance of detonation and underwater explosion (UNDEX) of a six‐formula HMX‐based aluminized explosive was examined by detonation and UNDEX experiments. The detonation pressures, detonation velocities, and detonation heat of HMX‐based aluminized explosive were measured. The reliability between the experimental results and those calculated by an empirical formula and the KHT code was verfied. UNDEX experiments were carried out on the propagation of a shock wave and a bubble pulse of a 1 kg cylindrical HMX‐based aluminized explosive underwater at a depth of 4.7 m. Based on the experimental results of the shock wave, the coefficients of similarity law equation for the peak pressure and attenuation time constant of shock wave were in acceptable agreement. The bubble motion during UNDEX was simulated using MSC.DYTRAN software, and the radius time curves of bubbles were determined. The effect of the aluminum/oxygen ratio on the performance of the detonation and UNDEX for an HMX‐based aluminized explosive was discussed.     

A Simple and Rapid Evaluation of Explosive Performance – The Disc Acceleration Experiment

It is crucial in the development of a new explosive to obtain an evaluation of performance early in the process when the availability of material is limited. Evaluation requires dynamic measurements of detonation velocity, pressure, and expansion energy – typically in separate experiments that require large amounts of material, time, and expense. There is also a need for evaluation of the total available thermodynamic energy. The dynamic evaluations, in particular, have been a major hindrance to development of new explosives. The new experimental testing method to be described here requires small charges and obtains accurate measurement of all three of the detonation performance characteristics in a single test. The design, a Disc Acceleration eXperiment (DAX), provides an initial condition of steady detonation and a charge‐geometry amenable to 2D hydrodynamic simulations. The velocity history of a metal disk attached to the end of the explosive charge is measured with Photonic Doppler Velocimetry (PDV). This disc velocity data is analyzed to give both CJ pressure and expansion energy. The detonation velocity is obtained with probes along the charge length. The experiments and subsequent analyses are concentrated on LX‐16, a known PETN based explosive, for the purpose of establishing the accuracy of the method and to provide a standard for comparison with other explosives. We present details of the experimental design and also detonation velocity and PDV results from a number of experiments. The total available internal energy for the explosive was obtained from published detonation calorimetry measurements by Ornellas [1], and from thermodynamic equilibrium calculations. An equation‐of‐state (EOS) for LX‐16 was derived from hydrodynamic simulations of thin plate‐push velocity‐time data. We will show a successful comparison with a previously published Jones‐Wilkins‐Lee (JWL) EOS for PETN by Green and Lee [2–4].     

Nanocomposite Formation in Hydrogenated Nitrile Rubber (HNBR)/Organo‐Montmorillonite as a Function of the Intercalant Type

Summary: Hydrogenated acrylonitrile butadiene rubber (HNBR) was melt compounded with montmorillonite (MMT) and organophilic modified MMTs prior to sulfur curing. In contrast to the micro‐composite formation resulting from the compounding of the HNBR and pristine MMT, the modified MMTs (i.e., octadecylamine: MMT‐ODA, octadecyltrimethylamine: MMT‐ODTMA, methyltallow‐bis(2‐hydroxyethyl) quaternary ammonium: MMT‐MTH intercalants) produced nanocomposites. It was found that the organoclay with primary amine intercalant (cf. MMT‐ODA) gave confined structures along with the exfoliated/intercalated structures. This was traced to its reactivity with the curatives. By contrast, the organoclays containing less reactive quaternary ammonium compounds (cf. MMT‐ODTMA, MMT‐MTH) were exfoliated and intercalated based on X‐ray diffraction (XRD) and transmission electron microscopy (TEM) results. The hydroxyl functional groups of the MMT‐MTH supported the clay dispersion. The better adhesion between MMT‐MTH and HNBR was explained by hydrogen bonding between the hydroxyl groups of the intercalant and the acrylonitrile group of the HNBR matrix. This HNBR/MMT‐MTH nanocomposite showed the best mechanical properties as verified by tensile mechanical tests and dynamic mechanical thermal analysis (DMTA). The high tensile strength along with the high elongation at break for the rubber nanocomposites were attributed to the ability of the ‘clay network’ to dissipate the input energy upon uniaxial loading.

Scheme of failure development in rubber/organoclay mixes with poor (a) and good (b) dispersion of the clay layers.     

Damage of a High‐Energy Solid Propellant and Its Deflagration‐to‐Detonation Transition

In order to assess the safety of high‐energy solid propellants, the effects of damage on deflagration‐to‐detonation transition (DDT) in a nitrate ester plasticized polyether (NEPE) propellant, is investigated. A comparison of DDT in the original and impacted propellants was studied in steel tubes with synchronous optoelectronic triodes and strain gauges. The experimental results indicate that the microstructural damage in the propellant enhances its transition rate from deflagration to detonation and causes its increased sensitivity. It is suggested that the mechanical properties of the propellant should be improved to reduce its damage so that the probability of DDT might be reduced.     

The Insensitive Energetic Material Trifurazano‐oxacycloheptatriene (TFO): Synthesis and Detonation Properties

The high‐energy insensitive compound trifurazano‐oxacycloheptatriene (TFO) was first by synthesized through special etherification. The reaction mechanism and reaction conditions were discussed. TFO has a low melting point (78.6 °C) and good compatibility. TFO is insensitive to impact and friction and has similar detonation velocity (7.7 km s⁻¹) and detonation pressure (35.6 GPa) to RDX.     

Detonation Energies from the Cylinder Test and CHEETAH V3.0

The cylinder test for deriving detonation energies is fully described and analyzed, including the relation between streak camera and Fabry‐Perot interferometer data. The 6, 12.5 and 19 mm scaled displacements are modified to represent average relative volumes of 2.2, 4.4 and 7.2. CHEETAH V3.0 is introduced with its new all‐Hugoniot calibration, which produces the most accurate detonation energies to date. Using CHEETAH V3.0 energies at the three cylinder volumes, we find that 107 cylinder shots show full burn. Of these, 52 are taken as standards with an error of ±2.6 %. Another 26 show higher energies, which cannot be explained. Finally, 111 shots show lower energies and these are taken to represent slow kinetics. The composite explosive PBXN‐111 is taken as a special problem, because unconfined and confined Size Effect data plus two different‐size cylinder tests have been done. The form of JWL++ with one fully‐reacted JWL, as copied from Ignition & Growth, failed to fit the data. The two rate constants interact too strongly, so that the form works for 90 % cylinder energies but not for the 25 % found in PBXN‐111. We, therefore, constructed a 2‐JWL form with the first, fast rate describing the detonation velocity and the second, slow rate the cylinder energies. This form of JWL++ isolates the rate constants and works for slow‐reacting explosives. The simple form of JWL++ allows the fast and slow rates to be estimated directly from the data. The Gurney velocity divided by the detonation velocity for the standard explosives is found to be 0.30, 0.33, 0.34 and 0.35 for the relative volumes v=2.2, 4.4, 7.2 and the maximum measured.     

Tribological properties of micro‐ and nanoparticles‐filled poly(etherimide) composites

It has been found that nano‐ or microsized inorganic particles in general enhance the tribological properties of polymer materials. In the present study, 5 vol % nano‐TiO₂ or micro‐CaSiO₃ was introduced into a polyetherimide (PEI) matrix composite, which was filled additionally with short carbon fibers (SCF) and graphite flakes. The influence of these inorganic particles on the sliding behavior was investigated with a pin‐on‐disc testing rig at room temperature and 150°C. Experimental results showed that both particles could reduce the wear rate and the frictional coefficient (μ) of the PEI composites under the applied testing conditions. At room temperature, the microparticles‐filled composites exhibited a lower wear rate and μ, while the nano‐TiO₂‐filled composites possessed the lowest wear rate and μ at elevated temperature. Enhancement in tribological properties with the addition of the nano‐particles was attributed to the formation of transfer layers on both sliding surfaces together with the reinforcing effect. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1678–1686, 2006     

A novel composite binder design for direct ink writing alumina-based ceramics with enhanced strength at low sintering temperature

Direct ink writing (DIW), an extrusion-based additive manufacturing method, has been proposed as a versatile process for preparing ceramics for structural and functional applications. However, controlling the strength of ceramics during processing remains a challenge. In this study, a novel composite binder system consisting of aqueous polyvinylpyrrolidone solution and Al(H₂PO₄)₃ gel was adopted for the DIW of alumina ceramics. Throughout the process, the mechanical performance, dimensional shrinkage, phase compositions and microstructure of samples were evaluated. The results indicate that the composite binder improves green strength by generating hydrogen bonding, which considerably enhances the strength of alumina ceramics under low-temperature sintering due to the reaction between Al(H₂PO₄)₃ gel and nanosized clay particles. This also promotes the high-temperature sintering performance of Al₂O₃-based ceramics. Overall, the current composite binder is anticipated to be promising for DIW of alumina ceramics, providing sufficient strength for post-processing and greatly improving strength after low-temperature sintering.     

Rheological behavior and thermal properties of poly(butyl acrylate‐co‐2‐ethylhexyl acrylate)‐grafted vinyl chloride resin

The rheological behavior and thermal properties of a poly(butyl acrylate‐co‐2‐ethylhexyl acrylate) [P(BA‐EHA)]‐grafted vinyl chloride (VC) composite resin [P(BA‐EHA)/poly(vinyl chloride) (PVC)] and its materials were investigated. The rheological behavior, thermal stability, and Vicat softening temperature (VST) of P(BA‐EHA)/PVC were measured with capillary rheometry, thermal analysis, and VST testing, respectively. The effects of the P(BA‐EHA) content and the polymerization temperature of grafted VC on the rheological behavior of the composite resin were examined. The weight loss of the composite resin and its extracted remainder via heating were analyzed. The influence of the content and crosslinking degree of P(BA‐EHA) and the polymerization temperature of the grafted VC on VST of the materials was determined. The results indicated the pseudoplastic‐flow nature of the composite resin. The flow property of the modified PVC resin was improved because of the incorporation of the acrylate polymer. The molecular weight of PVC greatly influenced the flow behavior and VST of the composite resin and its materials. The flowability of the composite resin markedly increased, and the VST of its materials decreased as the polymerization temperature of the grafted VC increased. The initial degradation temperature of the composite resin increased as the P(BA‐EHA) content increased. The VST of the samples was enhanced a little as the content of the crosslinking agent increased in P(BA‐EHA). As expected, the composite resin, with good impact resistance, had better heating stability and flowability than pure PVC, whereas the VST of the material decreased little with increasing P(BA‐EHA) content. Therefore, P(BA‐EHA)/PVC resins prepared by seeded emulsion polymerization have excellent potential for widespread applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 419–426, 2005     

Time–temperature superposition principle applied to a kenaf‐fiber/high‐density polyethylene composite

The time–temperature superposition principle was applied to the viscoelastic properties of a kenaf‐fiber/high‐density polyethylene (HDPE) composite, and its validity was tested. With a composite of 50% kenaf fibers, 48% HDPE, and 2% compatibilizer, frequency scans from a dynamic mechanical analyzer were performed in the range of 0.1–10 Hz at five different temperatures. Twelve‐minute creep tests were also performed at the same temperatures. Creep data were modeled with a simple two‐parameter power‐law model. Frequency isotherms were shifted horizontally and vertically along the frequency axis, and master curves were constructed. The resulting master curves were compared with an extrapolated creep model and a 24‐h creep test. The results indicated that the composite material was thermorheologically complex, and a single horizontal shift was not adequate to predict the long‐term performance of the material. This information will be useful for the eventual development of an engineering methodology for creep necessary for the design of structural building products from these composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1995–2004, 2005     

LX‐17 Corner‐Turning

We have performed a series of highly‐instrumented experiments examining corner‐turning of detonation. A TATB booster is inset 15 mm into LX‐17 (92.5% TATB, 7.5% kel‐F) so that the detonation must turn a right angle around an air well. An optical pin located at the edge of the TATB gives the start time of the corner‐turn. The breakout time on the side and back edges is measured with streak cameras. Three high‐resolution X‐ray images were taken on each experiment to examine the details of the detonation. We have concluded that the detonation cannot turn the corner and subsequently fails, but the shock wave continues to propagate in the unreacted explosive, leaving behind a dead zone. The detonation front farther out from the corner slowly turns and eventually reaches the air well edge 180° from its original direction. The dead zone is stable and persists 7.7 μs after the corner‐turn, although it has drifted into the original air well area. Our regular reactive flow computer models sometimes show temporary failure but they recover quickly and are unable to model the dead zones. We present a failure model that cuts off the reaction rate below certain detonation velocities and reproduces the qualitative features of the corner‐turning failure.     

COOHMWCNTs‐induced BiFeO3‐poly(vinylidene fluoride) (PVDF) composites with enhanced dielectric and ferroelectric properties

In this work, flexible three phase composite films were prepared with surface functionalized multi‐walled carbon nanotubes (f‐MWCNTs) and bismuth ferrite (BiFeO₃;BFO) particles embedded into the poly(vinylidene fluoride) (PVDF) matrix via solution casting technique. The properties and the microstructure of prepared composites were investigated using an impedance analyzer and field emission scanning electron microscope. The micro‐structural study showed that the f‐MWCNTs and BFO particles were dispersed homogeneously within the PVDF matrix, nicely seated on the floor of the f‐MWCNTs separately. The dielectric measurement result shows that the resultant composites with excellent dielectric constant (≈96) and relatively lower dielectric loss (<0.23 at 100 Hz). Furthermore, the percolation theory is explored to explain the dielectric properties of the resultant composites. It says that the percolation threshold of f_MWCNTs = 0.9 wt % and the enhancement of the dielectric constant of the composite was also discussed. In addition, the remnant polarization of the un‐poled PVDF‐BFO‐f‐MWCNTs composites (2P_r ～1.34 µC/cm² for 1.1 wt % of f‐MWCNTs) is also improved. These three phase composites provide a new insight to fabricate flexible and enhanced dielectric properties as a promising application in modern electrical and electronic devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46002.     

COOH?MWCNTs‐induced BiFeO3‐poly(vinylidene fluoride) (PVDF) composites with enhanced dielectric and ferroelectric properties

In this work, flexible three phase composite films were prepared with surface functionalized multi‐walled carbon nanotubes (f‐MWCNTs) and bismuth ferrite (BiFeO₃;BFO) particles embedded into the poly(vinylidene fluoride) (PVDF) matrix via solution casting technique. The properties and the microstructure of prepared composites were investigated using an impedance analyzer and field emission scanning electron microscope. The micro‐structural study showed that the f‐MWCNTs and BFO particles were dispersed homogeneously within the PVDF matrix, nicely seated on the floor of the f‐MWCNTs separately. The dielectric measurement result shows that the resultant composites with excellent dielectric constant (≈96) and relatively lower dielectric loss (<0.23 at 100 Hz). Furthermore, the percolation theory is explored to explain the dielectric properties of the resultant composites. It says that the percolation threshold of f_MWCNTs = 0.9 wt % and the enhancement of the dielectric constant of the composite was also discussed. In addition, the remnant polarization of the un‐poled PVDF‐BFO‐f‐MWCNTs composites (2P_r ～1.34 µC/cm² for 1.1 wt % of f‐MWCNTs) is also improved. These three phase composites provide a new insight to fabricate flexible and enhanced dielectric properties as a promising application in modern electrical and electronic devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46002.     

A Miniature Device for Shock Initiation of Hexanitrostilbene by High‐Speed Flyer

A miniature device for shock initiation of the hexanitrostilbene (HNS) through micro‐charge detonation‐driven flyer was fabricated. This device consisted of the substrate, micro‐charge, flyer, and barrel. Four types of flyer (titanium of 28 μm, aluminum of 22 μm, copper of 22 μm and polyimide (PI) of 55 μm in thickness) were studied and the effect of micro‐charge thickness, diameter, and barrel length were investigated by measuring the average flyer velocities using polyvinylidene fluoride (PVDF) films. The results show that the titanium flyer is more proper for such initiation device compared to aluminum, copper, and polyimide flyer. The average velocity of the flyer increased with the thickness of micro‐charge and the increment was larger when the thickness increases from 0.3 mm to 0.4 mm than when the thickness increases from 0.4 mm to 0.6 mm. The flyer velocity significantly increased with the increase in the diameter of micro‐charge until a plateau appeared at 0.8 mm. The flyer velocity increased first and then decreased sharply with the increase in barrel length. The average velocity for a 28 μm thick titanium flyer was measured to be as high as 2468 m s⁻¹ when the thickness, micro‐charge diameter and the length of barrel were 0.6 mm, 0.8 mm and 659 μm, respectively. The HNS‐IV explosive with density 1.57 g cm⁻³ was initiated by this miniature device.     

Dynamic Fragmentation and Blast from a Reactive Material Solid

Structural reactive material (SRM) is consolidated from a fine granular mixture of reactive materials towards the mixture theoretical maximum density with little porosity, thus bearing both high energy density and mechanical strength. A reactive hot spot concept was investigated for fine fragmentation of a SRM solid under explosive loading to augment air blast through rapid reaction of fine SRM fragments. In this concept, micro‐sized reactive materials were distributed in a fuel‐rich SRM solid, such as MoO₃ particles consolidated in a particulate aluminum base in 10Al+MoO₃. Intermetallic reactions of micro‐sized MoO₃ and nearby Al under explosive loading created heat and gas products to form microscale hot spots that initiated local fractures leading to fine fragments of the rest of Al. The SRM solid was made of a thick‐walled cylindrical casing, containing a high explosive in a detonation pressure range of 25–34 GPa with a casing‐to‐explosive mass ratio of 1.78. Experiments in a cylindrical chamber demonstrated the presence of a large amount of fine SRM fragments, whose reaction promptly after detonation significantly enhanced the primary and near field blast wave, as compared to the results from a baseline pure Al‐cased charge, thus indicating the feasibility of the concept.     

Assessing biodegradability and mechanical,thermal, and morphological properties of an acrylic acid‐modified poly(3‐hydroxybutyric acid)/wood flours biocomposite

A poly(3‐hydroxybutyric acid) and wood flours (PHB/wood flours) composite and an acrylic acid‐grafted PHB/wood flours composite were characterized and their properties were examined and compared. Mechanical properties of PHB became significantly worse when it was blended with wood flours, due to the poor compatibility between the two phases. Much better dispersion and homogeneity of wood flours in the polymer matrix was obtained when PHB‐g‐acrylic acid (AA) was used in place of PHB in the composite. Improved mechanical and thermal properties of the PHB‐g‐AA/wood flours composite, notably an increase in tensile strength at breakpoint, evidenced its superiority to the PHB/wood flours composite. Furthermore, PHB‐g‐AA/wood flours composites were more easily processed because of their lower melt viscosity. Under soil and enzymatic environments, weight loss data indicated that both composites were more biodegradable with higher wood flours content. A reduction in tensile strength at break after exposure to soil and enzymatic environments was also observed in both blends, especially at high wood flours content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3565–3574, 2006