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• The analysis model for jacket fragmentation and dispersion of reactive PELE was proposted. • The radial velocity of jacket fragment significantly depends on the radial energy density. • The deflagration reaction of the reactive filling increases the maximum radial velocity of the jacket fragments by more than 40 %. • The two-step segmented numerical simulation effectively simulates the reactive PELE impacting plate. Comparing with traditional PELE, the reactive PELE shows a more significant lateral enhancement effect due to the deflagration reaction of the filling by impact. Here an analytical model for thin-walled jacket fragmentation and dispersion is presented based on the wave interaction and the reaction of reactive filling. Subsequently, a two-step segmented numerical simulation for the impact deflagration of reactive PELE is developed. Based on the numerical simulation, the wave interaction process and the internal stress distribution of the filling were given firstly, then the deflagration reaction of reactive filling, jacket fragmentation and dispersion were simulated. By the theory and simulation, the experiment results of reactive PELE impacting steel plate are analyzed. In the experiment, the thickness of the front steel target is 6mm-20 mm, and the multi-layer witness aluminum plate is set behind the steel target to obtain the lateral effect of the reactive PELE. The analysis results show that the released energy of the reactive filling increases the maximum radial velocity of the jacket fragments by more than 40 %, and the perforation dispersion on the witness plate significantly depends on the filling reaction level and the front steel plate thickness, the lateral enhancement mechanism of reactive PELE impacting plate is explained. [ABSTRACT FROM AUTHOR]

Reactive material fragment is an extremely efficient damage enhancement technology that incorporates the defeat mechanisms of kinetic energy and chemical energy. In this paper, the polymer-based reactive material fragment/target interactions are investigated. Related dynamic testing techniques for energy release characteristics of reactive material fragments are presented, and a series of ballistic experiments is conducted. The results show the reactive material fragment, which perforates the closed test chamber, undergoes a violent chemical reaction under highly dynamic loads and releases great amounts of thermo-chemical energy on the interior. The impact-initiated process and energy release behavior are markedly influenced by the impact velocity, indicating the material's fracture is of importance to the reaction. A relationship between the maximum pressure inside the chamber and the reaction efficiency is derived to analyze the influence quantitatively, and the venting effects are also considered. [ABSTRACT FROM AUTHOR]

The influence of microstructure on the response of energetic structural materials (ESMs) under shock conditions remains inadequately quantified, and the energy release process is not thoroughly understood. In this work, taking the classical Ni/Al ESM as an example, the shock response was investigated by the shock compression theory with the microstructure-based chemical reaction kinetics model. This theory mainly refers to the equation of the state of multi-component materials with mixture rule, and the reaction at the particle contact interface is built to form the multiscale thermodynamics model. The physical states of material after shock, including relative volume, temperature, and extent of reaction, were analyzed. The results revealed the effect of the burn velocity, particle size and molar ratio on the shock response. Furthermore, the model facilitates a comprehensive understanding of energy release, the extent of the intermetallic reaction, and the oxidation reaction. Despite the involvement of only a small portion of materials in the oxidation reaction, the energy release proportion was comparable to that of the intermetallic reaction. Additionally, insights into the effect of the microstructure on the energy release revealed by the model matched the tests well. [ABSTRACT FROM AUTHOR]

Aimed at finding out the influence degree of temperature, strain rate, water to cement ratio (w/c ratio) and maximum aggregate size on dynamic behavior of cement concrete, an orthogonal test on dynamic compressive strength of cement concrete applying a self-designed low temperature split Hopkinson pressure bar (SHPB) apparatus has been conducted on 8 groups of cylindrical cement concrete specimens (74 mm diameter and 34 mm thickness). The dynamic compressive strength of concrete specimens with different w/c ratios (0.5, 0.6) and maximum aggregate sizes (12 mm, 22 mm) have been tested at different temperatures (28 °C, 0 °C, −15 °C, −30 °C) and strain rates (33.5 s −1 , 46.7 s −1 ). The influence sequence of factors is: temperature > strain rate > w/c ratio > maximum aggregate size. According to the results of orthogonal test, a further experimental study concerning the influence of temperature (28 °C, 0 °C, −15 °C, −30 °C, −45 °C, −60 °C, −75 °C) and strain rate (34.33 s −1 , 44.25 s −1 , 63.18 s −1 ) on dynamic compressive strength of concrete has been conducted on 21 groups of cylindrical specimens. Also a mechanical calculation model has been built for force analysis. The results demonstrate that: When −75 °C < T < 28 °C, increase ratio of specific energy absorption (SEA) rises as temperature decreases; the sensitivity of dynamic compressive strength to strain rate increases as temperature decreases; the relationship between dynamic compressive strength and temperature conforms to a growth curve, and finally the increase ratio of dynamic compressive strength stabilizes at a maximum level of 65% at T = −75 °C. [ABSTRACT FROM AUTHOR]

In order to investigate the failure and ejection behavior of concrete materials under internal blast, the default Riedel-Hiermaier-Thoma (RHT) concrete model in AUTODYN and a meshfree processor called SPH are employed in this numerical simulation. It is shown that the failure mechanisms are significantly different in these damaged zones. Crushed zone is caused by shear failure while fractured zone is induced by tensile failure, and spalled zone is formed by a combination of shear and tensile failure. In addition, the ejection velocity distribution of the fragmented concrete mass on free surface is examined. The results indicate that the ejection velocity declines monotonously with the increase of the distance to symmetry axis of computational model. On the wall of the prefabricated borehole, two types of fragmented concrete mass are analyzed, and bottom initiation is recommended to eject the fragmented concrete mass effectively. Moreover, an algorithm of average ejection speed is developed to effectively estimate the drill capacity of high velocity, energetic (HE) projectiles. At last, the validity of numerical simulation is verified by physical experiments. [ABSTRACT FROM AUTHOR]

Highlights: [•] Response surface methodology (RSM) is used to study ASC’s freeze–thaw resistance. [•] The influence on the freeze–thaw resistance from high to low is A/S, slag content and sand ratio. [•] The interaction of A/S and slag content is the most prominent. [•] Air-void structure is a decisive factor, and space coefficient and specific surface area are related well to D F. [Copyright &y& Elsevier]

Reactive materials (RMs) are special type of impact-initiated energetic materials that have been widely studied with broad military application prospects. However, simulating the ignition and reaction of RMs using current numerical methods is difficult due to their complex mechanism related to high dynamic loads. In this work, based on a theoretical model consisting of impact ignition criteria and chemical reaction rate of polymer-based RMs, a numerical method with a unified equation of state was proposed and compiled as an executable program. Experiments consisting of typical polytetrafluoroethylene /Al RM projectiles impacting double-spaced plates were conducted and simulated using the user-compiled program, and the results verified the effectiveness of the numerical method. The simulation also qualitatively analyzed the second-collision induced reaction enhancement mechanism. In addition, the results revealed that the kinetic-chemical combined effect is a crucial factor that determined the damage enhancement effect on the rear plates. [ABSTRACT FROM AUTHOR]

Two-dimensional simulation models are established to investigate the impact-induced mechanical behavior of the PTFE/Al/W reactive materials. Random distribution of the metal particles and mesh generation of the specimen are obtained by using ANSYS parametric design language. Moreover, based on the experimental results of the Hopkinson bar, the loading curve in the simulation is simplified. Influences of the tungsten particle size, the particle distribution, and the loading strain rate on the mechanical behavior are analyzed by ANSYS/LS-DYNA. The results show that local severe deformation of the polytetrafluoroethylene (PTFE) matrix is generally caused by extrusion and slippage of the metal particles. The generation, growth, and interaction of the cracks are then induced gradually. Finally, many macrocracks form and the specimen dramatically fractures. Results also show that the local deformation of the PTFE matrix, deformation outline, and crack distribution are significantly influenced by the tungsten particle sizes and the particle distribution. In addition, with a decrease in the loading strain rate, the time for initial crack generation gradually delays and the deformation severity of the PTFE matrix shows a decrement. [ABSTRACT FROM AUTHOR]

A polymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride- (THV) based reactive materials (RMs) was designed to improve their density and energy release efficiency. The mechanical performances, fracture mechanisms, thermal behavior, energy release behavior, and reaction energy of four types of RMs (26.5% Al/73.5% PTFE, 5.29% Al/80% W/14.71% PTFE, 62% Hf/38% THV, 88% Hf/12% THV) were systematically researched by conducting compressive tests, scanning electron microscope (SEM), differential scanning calorimeter, thermogravimetric (DSC/TG) tests and ballistic experiments. The results show that the THV-based RMs have a unique strain softening effect, whereas the PTFE-based RMs have a remarkable strain strengthening effect, which is mainly caused by the different glass transition temperatures. Thermal analysis indicates that the THV-based RMs have more than one exothermic peak because of the complex component in THV. The energy release behavior of RMs is closely related to their mechanical properties, which could dominate the fragmentation behavior of materials. The introduction of tungsten (W) particles to PTFE RMs could not only enhance the density but also elevate the reaction threshold of RMs, whereas the reaction threshold of THV-based RMs is decreased when increasing Hf particles content. As such, under current conditions, the THV-based RMs (88% Hf/12% THV) with a high density of 7.83 g/cm3 are adapted to release a lot of energy in thin, confined spaces. [ABSTRACT FROM AUTHOR]

In order to study the microscopic reaction mechanism and kinetic model of Al/PTFE, a reactive force field (ReaxFF) was used to simulate the interface model of the Al/PTFE system with different oxide layer thicknesses (0 Å, 5 Å, 10 Å), and the thermochemical behavior of Al/PTFE at different heating rates was analyzed by simultaneous thermal analysis (TG-DSC). The results show that the thickness of the oxide layer has a significant effect on the reaction process of Al/PTFE. In the system with an oxide layer thickness of 5 Å, the compactness of the oxide layer changes due to thermal rearrangement, resulting in the diffusion of reactants (fluorine-containing substances) through the oxide layer into the Al core. The reaction mainly occurs between the oxide layer and the Al core. For the 10 Å oxide layer, the reaction only exists outside the interface of the oxide layer. With the movement of the oxygen ions in the oxide layer and the Al atoms in the Al core, the oxide layer moves to the Al core, which makes the reaction continue. By analyzing the reaction process of Al/PTFE, the mechanism function of Al/PTFE was obtained by combining the shrinkage volume model (R3 model) and the three-dimensional diffusion (D3 model). In addition, the activation energy of Al/PTFE was 258.8 kJ/mol and the pre-exponential factor was 2.495 × 1015 min−1. The research results have important theoretical significance and reference value for the in-depth understanding of the microscopic chemical reaction mechanism and the quantitative study of macroscopic energy release of Al/PTFE reactive materials. [ABSTRACT FROM AUTHOR]

Perforation behavior of 3 mm/3 mm double-spaced aluminum plates by PTFE/Al/W (Polytetrafluoroethylene/Aluminum/Tungsten) reactive projectiles with densities ranging from 2.27 to 7.80 g/cm3 was studied experimentally and theoretically. Ballistic experiments show that the failure mode of the front plate transforms from petalling failure to plugging failure as projectile density increases. Theoretical prediction of the critical velocities for the reactive projectiles perforating the double-spaced plates is proposed, which is consistent with the experimental results and well represents the perforation performance of the projectiles. Dimensionless formulae for estimating the perforation diameter and deflection height of the front plates are obtained through dimensional analysis, indicating material density and strength are dominant factors to determine the perforation size. High-speed video sequences of the perforation process demonstrate that high-density reactive projectiles make greater damage to the rear plates because of the generation of projectile debris streams. Specifically, the maximum spray angle of the debris streams and the crater number in the debris concentration area of the rear plate both increase with the projectile density and initial velocity. [ABSTRACT FROM AUTHOR]

A combination of mesoscale simulations and explosive loading experiments is used to investigate the shock response and shock-induced initiation behavior of aluminum-polytetrafluoroethylene (Al-PTFE) granular composites. A two-dimensional model following the random distribution of real Al particle sizes is developed and validated against experiments. The model is employed to investigate the effect of Al mass fractions on shock characterizes as well as Hugoniot relationships, and noticeable differences are visualized at the grain-level in the pressure, temperature, and strain response. Systematic shock structures in metals have been identified, and the underlying mechanisms of deformation and energy dissipation are discussed respectively. Results demonstrate that the high pressure is concentrated in the wave front, but a much greater heat and larger strain exhibit along grain/matrix interfaces that enable the friction dissipation the main mechanism of hot-spots formation. Specific quantities of critical temperature to initiate are obtained based on basic microstructure attributes to analyze the influence on hot-spots distribution by mass fractions. The interaction of shock wave with mesoscale heterogeneities accounts for the stochastic nature of the initiation process. Unlabelled Image • Mesoscale simulation combined with explosive loading tests is employed. • Grain-level mechanical, thermal responses, and Hugoniot relationships are obtained. • Plastic deformation and particle/particle friction lead to hot-spots. • Hot-spots distribution reveals the stochastic nature of the initiation process. [ABSTRACT FROM AUTHOR]

Aluminum (Al)-based reactive materials have recently attracted much attention due to their excellent chemical energy release characteristics. However, there still exists a great challenge to improve the mechanical properties and energy density of Al-based reactive materials. In this work, we reported that core–shell nano-aluminum@fluororubber (nAl@F2311) composites with good mechanical properties and high energy release characteristics were designed and fabricated by the electrical exploding wires method. The results showed that Al nanospheres were coated by F2311 uniformly to form the nAl@F2311 core–shell microstructure with high Al contents. Quasi-static/Split Hopkinson Pressure Bar dynamic compression test results showed axial splitting failure mode of nAl@F2311 composites. nAl@F2311-10 composites with 90 wt. % Al contents had higher compressive strength, with quasi-static and dynamic compressive strength of 117.6 and 304.6 MPa, respectively. nAl@F2311-15 composites with 85 wt. % Al contents had a lower ignition threshold. Furthermore, the impact-induced energy release test showed higher fluorine contents will accelerate energy release, reduce impact ignition threshold, and improve the reaction efficiency of nAl@F2311 composites. The high reaction efficiency (97.79%) of the nAl@F2311-15 composites was obtained at an impact velocity of 1090 m/s. This offered a concept-of-proof work to design and fabrication of nanostructured reaction materials, which had high strength and energy release performance. [ABSTRACT FROM AUTHOR]

In this research, the bulk density homogenization and impact initiation characteristics of porous PTFE/Al/W reactive materials were investigated. Cold isostatic pressed (CIPed) and hot temperature sintered (HTSed) PTFE/Al/W reactive materials of five different theoretical maximum densities were fabricated via the mixing/pressing/sintering process. Mesoscale structure characteristics of the materials fabricated under different molding pressures were compared while the effect of molding pressures on material bulk densities was analyzed as well. By using the drop weight testing system, effects of the theoretical maximum densities (TMDs), drop heights and molding pressures on the impact initiation characteristics were studied. Quantitatively, characteristic drop heights (H50) for different types of materials were obtained. The two most significant findings of this research are the density homogenization zone and the sensitivity transition zone, which would provide meaningful guides for further design and fabrication of reactive materials. [ABSTRACT FROM AUTHOR]

The penetration enhancement behaviors of a reactive material double-layered liner (RM-DLL) shaped charge against thick steel targets are investigated. The RM-DLL comprises an inner copper liner, coupled with an outer PTFE (polytetrafluoroethylene)/Al reactive material liner, fabricated via a cold pressing/sintering process. This RM-DLL shaped charge presents a novel defeat mechanism that incorporates the penetration capability of a precursor copper jet and the chemical energy release of a follow-thru reactive material penetrator. Experimental results showed that, compared with the single reactive liner shaped charge jet, a deeper penetration depth was produced by the reactive material-copper jet, whereas the penetration performance and reactive material mass entering the penetrated target strongly depended on the reactive liner thickness and standoff. To further illustrate the penetration enhancement mechanism, numerical simulations based on AUTODYN-2D code were conducted. Numerical results indicated that, with increasing reactive liner thickness, the initiation delay time of the reactive materials increased significantly, which caused the penetration depth and the follow-thru reactive material mass to increase for a given standoff. This new RM-DLL shaped charge configuration provides an extremely efficient method to enhance the penetration damage to various potential targets, such as armored fighting vehicles, naval vessels, and concrete targets. [ABSTRACT FROM AUTHOR]

Polytetrafluoroethylene/aluminum (PTFE/Al) reactive material is a pivotal research object in the aerospace, military, and mechanical engineering fields and can release chemical energy (CE) under shock or impact. However, its relatively low mechanical strength limits its applications. The present paper proposes a Cu-PTFE/Al (73.5wt. %/26.5wt. %) double-layer liner that can form tandem explosive formed projectiles (EFPs) under the shock of shaped charges, which not only retains the strong penetration ability but also shows a more significant lateral enhancement effect through the deflagration reaction. Here, the preparation process of the PTFE/Al liner is given, and an analytical model for the Cu-PTFE/Al tandem EFP of the damage process against multi-spaced plates is established, revealing the penetration and deflagration-enhanced mechanisms. Subsequently, a two-step segmented numerical simulation for the penetration–deflagration coupling effects is conducted, and the time-space interaction process and damage results between kinetic energy penetration and CE deflagration are obtained. A series of experiments of tandem EFPs against spaced plates are conducted, including the different materials, thickness ratio, and standoff. Experimental results show that compared with Cu–Cu tandem EFP with the same condition, the penetration ability of Cu-PTFE/Al composite EFP is reduced, but the damage enhancement effect is greatly improved; the maximum damage area of a single plate is increased by 220.1%, and the average damage area of a single plate is increased by 76.2%. This study provides important reference data and a theoretical basis for the design of metal-reactive tandem EFPs. [ABSTRACT FROM AUTHOR]

The chemical reaction mechanism of Ni/Al composites, referring to the exothermic mechanism and intermetallic-forming mechanism, is investigated by using molecular dynamics simulation. During the exothermic process, the influences of Ni/Al atomic ratios and crystallographic orientations on the exothermic reaction are systematically investigated. The exothermic mechanism can be explained by the atomic diffusion that increases the quantity of Ni–Al chemical bonds. There are two pathways to form the intermetallic phase during the chemical reaction. One is the atomic diffusion that forms the B2 NiAl phase at the interface. The other way is quenching the sample to the room temperature, but the type of intermetallic phases depends on the Ni/Al atomic ratio and ignition temperature. [ABSTRACT FROM AUTHOR]

With the improvement of protection technology, the damage power of conventional penetrators has become increasingly inferior. Reactive material is a new type of energetic material, which has strong energy release capabilities under high-velocity-impact conditions. In this paper, the reactive materials were put into the penetrator, and its penetration characteristics were studied. First, the penetrator with enhanced lateral effect (PELE) projectile structure with better penetration capability was obtained by numerical simulation. Then, based on the established polytetrafluoroethylene (PTFE)/Al reactive material reaction model, the numerical simulation and experimental research of the PELE projectile with a reactive inner core penetrating the target were carried out. The results show that the simulation results are in good agreement with the experimental results, which verifies the confidence of the numerical simulation. The PELE projectile had a significant increase in power with the use of a truncated conical head and reactive materials. The residual velocity of the truncated cone PELE projectile increases by 8.41–21% over conventional PELE projectiles. Its damage range is 43% higher than that of conventional penetrators. The simulation method and the conclusions obtained in this paper can provide support and reference for further research on reactive materials and on effectively improving the damage power of the penetrator. [ABSTRACT FROM AUTHOR]

Fractal theory is introduced in fracture surface research of alkali-slag concrete (ASC) under freeze-thaw cycles; crack distribution of ASC fracture surface and freeze-thaw damage zone were calculated. Through fractal analysis of ASC sample fracture surfaces, relevance between section fractal dimension and fracture toughness and relationship between material composition and section fractal dimension are clarified. Results show that the specimen’s cracks before freeze-thaw extend along force direction gently, and there are more twists and turns after freezing and thawing; the fractal dimension D also grows from 1.10 to 1.33. SEM internal microcracks’ D of ASC internal microstructure after freezing and thawing is 1.37; 0 to 300 times ASC fractal dimension under freezing and thawing is between 2.10 and 2.23; with freeze-thaw times increasing, ASC fracture toughness decreases and fractal dimension increases, the fractal dimension and fracture toughness have a good linear relationship, and the fractal dimension can reflect the toughening effect of ASC. It is very feasible to evaluate ASC fracture behaviour under freezing and thawing with the fractal theory. Fractal dimension generally increases with activator solution-slag (A/S for short) or slag content. The greater the amount of A/S or slag content, the lower the dimension. [ABSTRACT FROM AUTHOR]

Existing research on PTFE-based reactive materials (RMs) mostly focuses on Al/PTFE RMs. To explore further possibilities of formulation, the reactive metal components in the RMs can be replaced. In this paper, Zr/PTFE and Ti/PTFE RMs were prepared by cold isostatic pressing and vacuum sintering. The static and dynamic compressive mechanical properties of Zr/PTFE and Ti/PTFE RMs were investigated at different strain rates. The results show that the introduction of zirconium powder and titanium powder can increase the strength of the material under dynamic loading. Meanwhile, a modified J-C model considering strain and strain rate coupling was proposed. The parameters of the modified J-C model of Zr/PTFE and Ti/PTFE RMs were determined, which can describe and predict plastic flow stress. To characterize the impact-induced reaction behavior of Zr/PTFE and Ti/PTFE RMs, a quasi-sealed test chamber was used to measure the over-pressure induced by the exothermic reaction. The energy release characteristics of both materials were more intense under the higher impact. [ABSTRACT FROM AUTHOR]

Polytetrafluoroethylene (PTFE)/aluminum (Al)-based energetic material is a kind of energetic material with great application potential. In this research, the control of the shock-induced energy release characteristics of PTFE/Al-based energetic material by adding oxides (bismuth trioxide, copper oxide, molybdenum trioxide, and iron trioxide) was studied by experimentation and theoretical analysis. Ballistic impact experiments with impact velocity of 735~1290 m/s showed that the oxides controlled the energy release characteristics by the coupling of impact velocities and oxide characteristics. In these experiments, the overpressure characteristics, including the quasi-static overpressure peak, duration, and impulse, were used to characterize the energy release characteristics. It turned out that when the nominal impact velocity was 735 m/s, the quasi-static overpressure peak of PTFE/Al/MoO3 (0.1190 MPa) was 1.99 times higher than that of PTFE/Al (0.0598 MPa). Based on these experimental results, an analytical model was developed indicating that the apparent activation energy and impact shock pressure dominated the energy release characteristic of PTFE/Al/oxide. This controlling mechanism indicated that oxides enhanced the reaction after shock wave unloading, and the chemical and physical properties of the corresponding thermites also affected the energy release characteristics. These conclusions can guide the design of PTFE-based energetic materials, especially the application of oxides in PTFE-based reactive materials. [ABSTRACT FROM AUTHOR]

Reactive material (RM) is a special kind of energetic material that can react and release chemical energy under highly dynamic loads. However, its energy release behavior is limited by its own strength, showing unique unsustainable characteristics, which lack a theoretical description. In this paper, an impact-initiated chemical reaction model is proposed to describe the ignition and energy release behavior of Al/PTFE RM. The hotspot formation mechanism of pore collapse was first introduced to describe the decomposition process of PTFE. Material fragmentation and PTFE decomposition were used as ignition criteria. Then the reaction rate of the decomposition product with aluminum was calculated according to the gas-solid chemical reaction model. Finally, the reaction states of RM calculated by the model are compared and qualitatively consistent with the experimental results. The model provides insight into the thermal-mechanical-chemical responses and references for the numerical simulation of impact ignition and energy release behavior of RM. [ABSTRACT FROM AUTHOR]

Quasi-static tension tests, quasi-static compression tests and dynamic compression tests were conducted to investigate the mechanical properties, constitutive behaviors and failure criteria of aluminum-polytetrafluoroethylene-tungsten (Al-PTFE-W) reactive materials with W content from 20% to 80%. The analysis of the quasi-static test results indicated that the strength of the materials may be independent of the stress state and W content. However, the compression plasticity of the materials is significantly superior to its tension plasticity. W content has no obvious influence on the compression plasticity, while tension plasticity is extremely sensitive to W content. Dynamic compression test results demonstrated the strain rate strengthening effect and the thermal softening effect of the materials, yet the dynamic compression strengths and the strain rate sensitivities of the materials with different W content show no obvious difference. Based on the experimental results and numerical iteration, the Johnson–Cook constitutive (A, B, n, C and m) and failure parameters (D1~D5) were well determined. The research results will be useful for the numerical studies, design and application of reactive materials. [ABSTRACT FROM AUTHOR]

In recent years, polytetrafluoroethylene (PTFE)/aluminum (Al) energetic materials with high-energy density have attracted extensive attention and have broad application prospects, but the low-energy release efficiency restricts their application. In this paper, oxide, bismuth trioxide (Bi2O3) or molybdenum trioxide (MoO3) are introduced into PTFE/Al to improve the chemical reaction performance of energetic materials. The pressurization characteristics of PTFE/Al/oxide as pressure generators are compared and analyzed. The experiments show that the significantly optimized quasi-static pressure peak, impulse, and energy release efficiency (0.162 MPa, 10.177 s·kPa, and 0.74) are achieved for PTFE/Al by adding 30 wt.% Bi2O3. On the other hand, the optimal parameter obtained by adding 10% MoO3 is 0.147 MPa, 9.184 s·kPa, and 0.68. Further, the mechanism of enhancing the energy release performance of PTFE/Al through oxide is revealed. The mechanism analysis shows that the shock-induced energy release performance of PTFE/Al energetic material is affected by the intensity of the shock wave and the chemical reaction extent of the material under the corresponding intensity. The oxide to PTFE/Al increases the intensity of the shock wave in the material, but the chemical reaction extent of the material decreases under the corresponding intensity. [ABSTRACT FROM AUTHOR]

Spherical explosives had regular shape and smooth surface, which gave them low sensitivity, excellent flowability, and high bulk density, thereby yield good charging performance. Traditional spherization methods always resulted in irregular shape, low sphericity, and uneven size. In this paper, a novel droplet microfluidic technology was used to fabricate hexanitrostilbene (HNS) microspherical with nitrocellulose (NC) as adhesive. The farication process (e. g., HNS concentration, NC concentration, flow rate) was fully investigated in pursuing for the ideal farication condition. The chemical structures, crystalline structures, and thermal stability of HNS were preserved. Meanwhile, the flowability and bulk density of HNS microspheres were significantly improved (Repose angle: HNS microsphere vs raw HNS, 33.1 vs 39.2°; bulk density: HNS microsphere vs raw HNS, 0.466 vs 0.301 g cm−3), which enhanced the charging and pressing performance of HNS. Unlabelled Image • Droplet microfluidics was firstly used for the spheroidization of HNS. • HNS microspheres with arrow size distribution were successfully synthesized. • The flowability of HNS microspheres were superior to that of raw HNS. • This work provided a novel method for the spheroidization of explosives. [ABSTRACT FROM AUTHOR]

The traditional polytetrafluoroethylene (PTFE)/Al reactive material liner shaped charge generally produces insufficient penetration depth, although it enlarges the penetration hole diameter by chemical energy release inside the penetration crater. As such, a novel high-density reactive material liner based on the PTFE matrix was fabricated, and the corresponding penetration performance was investigated. Firstly, the PTFE/W/Cu/Pb high-density reactive material liner was fabricated via a cold pressing/sintering process. Then, jet formation and penetration behaviors at different standoffs were studied by pulse X-ray and static experiments, respectively. The X-ray results showed that the PTFE/W/Cu/Pb high-density reactive material liner forms an excellent reactive jet penetrator, and the static experimental results demonstrated that the penetration depth of this high-density reactive jet increased firstly and then decreased by increasing the standoff. When the standoff was 1.5 CD (charge diameter), the penetration depth of this reactive jet reached 2.82 CD, which was significantly higher than that of the traditional PTFE/Al reactive jet. Moreover, compared with the conventional metal copper jet penetrating steel plates, the entrance hole diameter caused by this high-density reactive jet improved 29.2% at the same standoff. Lastly, the chemical reaction characteristics of PTFE/W/Cu/Pb reactive materials were analyzed, and a semi-empirical penetration model of the high-density reactive jet was established based on the quasi-steady ideal incompressible fluid dynamics theory. [ABSTRACT FROM AUTHOR]

• Impacted by the reactive materials filled projectile produces an interval rupturing damage to the multi-spaced aluminum plates. • The damage to aluminum plates strongly depends on the front steel plate's thickness. • The interval damage relies on chemical energy release by reactive material filling. • A theoretical model is developed to analyze the damage effects of aluminum plates. A series of experiments are performed to investigate the damage effect of multi-spaced metal plates impacted by the reactive materials filled projectile (RMFP) at a velocity about 1100 m s −1. The RMFP is a structural penetrator by replacing projectile's usually inert core with reactive material. The multi-spaced metal plates consist of a front steel plate followed by five aluminum plates. The front steel plates used have thicknesses of 10, 20, and 30 mm. All five spaced aluminum plates are 3 mm thick with the same spaced distance of 300 mm. The distance between the front steel plate and the first aluminum plate is 600 mm. The experimental results indicate an unusual interval rupturing damage phenomenon in the multi-spaced aluminum plates, revealing a strong dependence upon the thickness of the front steel plate: with increasing the thickness of the front steel plate from 10 mm to 30 mm, the damage to the first aluminum plate increases but the interval rupturing damage to the multi-spaced aluminum plates structure decreases significantly. Furthermore, to understand this unusual damage behavior, an analytical model is developed, by which the front steel plate's thickness effect on the interval rupturing damage to the multi-spaced aluminum plates is discussed. The model analysis shows that, with increasing the thickness of the front steel plate, the initiated reactive material filling length increases, resulting in a higher deflagration overpressure in the filling, greater radial expansion effects of the jacket, and shorter projectile remainder, thereby enhancing the rupturing damage to the aluminum plates near the front steel plate but reducing the rupturing damage to the other aluminum plates. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A novel nanocomposite of Si-incorporated SnO 2 with graphene is fabricated. • Si incorporation strengthens the interfacial bonding of nanocomposite. • Si incorporation promotes the electron/ion transport of nanocomposite. • The nanocomposite shows superior Li storage properties. Abstract SnO 2 -based anodes with high capacity are appealing for Li-ion batteries (LIBs). However, the large volume change and inferior cycling stability limit their practical application. To mitigate these problems, a novel nanocomposite of silicon-incorporated SnO 2 with graphene sheets (STOG) has been successfully fabricated as anode material for LIBs. Through a simple hydrolysis process, ultrafine Si-incorporated SnO 2 (STO) nanoparticles are uniformly loaded on the graphene sheets. Further it is found that Si incorporation brings about the Si O Sn bonding in the SnO 2 matrix and strengthens the Sn O C bonding between STO and graphene. These merits can enhance the structural stability and electron/ion transport of STOG nanocomposite, facilitating the reversible conversion of Sn–SnO 2. As a result, this STOG material delivers a high discharge capacity of 1117.8 mAh g−1 and retains 92.5% of the second capacity after 100 cycles at 0.1 A g−1. Furthermore, an excellent rate capacity of 683.9 mAh g−1 can be obtained at a high current of 1 A g−1. This work provides an effective way to design high-performance SnO 2 -based anode material for LIBs. [ABSTRACT FROM AUTHOR]

Highlights • Reactive jet penetrating thick steel plates show unusual damage behaviors. • Damage effects of thick steel plates strongly depended on reactive jet standoff. • Model predictions of damage to thick steel plates fit well with experiments. • Initiation delay time of reactive jet is the primary determinant mechanism. Abstract Reactive liner shaped charge jet (RLSCJ) penetrates thick steel plate by experiments and model analysis combined. The experimental reactive material liners with a density of about 2.3 g/cm3, composed of mass matched ratios of Al/PTFE powders, are consolidated by a cold pressing/sintering process. Four standoffs of 0.5, 1.0, 1.5, and 2.0 CD (charge diameter) are selected to conduct the penetration experiments. The experimental results show that, compared with traditional metal liner shaped charge jet against thick steel plates, a relative larger hole diameter but lower depth accompanying with fragmentation effects of penetrating steel plates are produced by RLSCJ. To understand this penetration behavior of reactive jet, an analytical model is developed to discuss the influence of initiation delay time of reactive jet and standoff on penetration depth. Analysis shows that the penetration depth strongly depends on initiation delay time of reactive jet. With increasing the initiation delay time, the penetration depth increases significantly, showing a good agreement with the experiments. Moreover, to further understand the fragmentation mechanism effect of the thick steel plates, the effective mass of reactive jet inside the penetrating hole and its deflagration-induced structural damage effect are analyzed theoretically. Prediction results fit well with the experiments, including crack generation and propagation in the thick steel plates, and the number of fragments. [ABSTRACT FROM AUTHOR]

Multi-element intermetallic energetic structural materials (ESMs) can be applied as reactive fragment, reactive shell and reactive shaped charge. As typical of intermetallics ESMs, Ni-Al ESMs have been heavily studied. However, the low density limits its application. This work proposed to improve the performance of Ni-Al ESMs by adding Ta. The nearly fully dense Ta-Ni-Al ESMs with a molar ratio 4:3:3 was successfully fabricated by explosive consolidation. The density was high up to 10.52 g/cm3 (98.3% theoretical maximum density). The heat treatment was used to further improve the performance of the Ta-Ni-Al ESMs. The microstructure characteristics were analyzed by scanning electron microscopy, X-ray diffraction and transmission electron microscope. The mechanical properties, reaction and impact-induced energy release have been systematically studied. Firstly, quasi-static and dynamic compression tests were conducted to analyze the mechanical properties of the sample before and after heat treatment. Secondly, the reaction characteristics in different atmospheres were discussed by differential scanning calorimetry and thermogravimetric analysis. The effect of the additive Ta was concerned. Furthermore, Impact-induced energy release tests on the Ta-Ni-Al ESMs were performed to understand the energy release properties. Based on these tests, the characterization of Ta-Ni-Al ESMs fabricated by explosive consolidation was obtained. There was no intermetallic formed in explosive consolidated samples. After the heat treatment, Ta-Ni-Al ESMs have good plasticity and strain rate effect. Meanwhile, under high impact velocity, the impact-induced energy release capability of Ta-Ni-Al ESMs was equivalent to Ni-Al ESMs. • Ta-Ni-Al ESMs with density of 10.56 g/cm3 was prepared by explosive consolidation. • The effect of the heat treatment on the mechanical properties is analyzed. • The effect of Ta on reaction characteristics of Al–Ni composite is investigated. • Under high impact velocity, the energy release capability of Ta-Ni-Al ESMs was equivalent to Ni-Al ESMs. [ABSTRACT FROM AUTHOR]

Ni–Al energetic structural materials (ESMs) has been widely applied in defense field, because of its good mechanical and energy release properties. The effects of the microstructure on mechanical and energy release properties of ESMs are not well understood. In this study, by designing the particle size Ni:Al = 1 μm:25 μm and Ni:Al = 20 μm:25 μm, two kinds of samples, Ni continuous phase (Ni cp) and Al continuous phase (Al cp), were prepared by explosive consolidation. The microstructure characteristics were analyzed by scanning electron microscopy, electron backscatter diffraction, and transmission electron microscope. Quasi-static and dynamic compression tests were also conducted to analyze the mechanical properties. It showed that the Ni cp ESMs had higher quasi-static compressive strength of 325 MPa and fracture strain of 21.3%, compared with the Al cp ESMs having the strength 275 MPa and the fracture strain 17.5%. Also, the dynamic compressive strength of the Ni cp ESMs sample is higher than that of the Al cp ESMs sample. The reaction characteristics of the two ESMs in different atmospheres were discussed by differential scanning calorimetry. The result showed that the reaction temperature of the Ni cp ESMs was lower. Impact-induced energy release tests on the two ESMs were performed to understand their energy release properties. The results showed that the microstructure had significant effects on the ignition velocity threshold and reaction efficiency. The Ni cp ESMs has better reaction performance because of the high interface density. • High dense Ni–Al ESMs is prepared by explosive consolidation. • Two different microstructures defined as Ni continuous phase and Al continuous phase are obtained. • The effect of the microstructure on the mechanical properties is analyzed. • The effect of the microstructure on the impact-induced energy release is evaluated. [ABSTRACT FROM AUTHOR]

Aiming at the problems in the highway runway clearance condition evaluation, according to the improved obstruction requirement of highway runway, the inner transitional surface (ITS) and outer transitional surface (OTS) range are calculated and analyzed in detail, the shape range of the ITS and OTS is pointed out, the methods of calculating the intersecting line and the key various points among ITS, runway strip (RS), inner horizontal surface (IHS) in terminal clearance zone (TCZ), including among OTS, IHS and outer horizontal surface (OHS) in side clearance zone (SCZ) are put forward. Furthermore, obstruction requirement when aircraft are placed on apron of the near highway sections is considered, then the corresponding steps of evaluation are proposed. The procedural design of highway runway clearance condition evaluation is realized by means of software to program. The superelevation condition of the obstacle in the clearance of the highway runway is calculated and analyzed by actual examples. All these have provided a theoretical basis for exactly determining the position, altitude and the superelevation value of the obstacle in the highway runway clearance zone. [ABSTRACT FROM AUTHOR]

Alkali-slag concrete (ASC) is prepared with Na 2 SiO 3 and NaOH composite activator. Fracture properties of ASC under freeze–thaw cycles are studied using response surface methodology (RSM), Design Expert software and Box–Behnken design (BBD). The RSM model of fracture toughness is built, then the influence law of sol ratio, slag content, age on fracture toughness is put forward. The relationship between initiation fracture toughness ( K IC Q ) and unstable fracture toughness ( K IC S ) is established. The influence law of freeze–thaw, sol ratio and slag content on K IC S is built, and the impact mechanism of the two factors on K IC S is analyzed. Results show that the RSM model fits well and can be used to analyze and predict ASC fracture toughness. The influential significance rank for K IC S is slag content > age > sol ratio, and the most significant interaction is between slag content and age. K IC Q is about 50–70% of K IC S , crack initiation should be the warning indicator of ASC structure. Fracture toughness decreases with the increased freeze–thaw times, whose declining rate and degree increase with sol ratio and slag content. With sol ratio increasing, more intense is the alkali slag reaction, reducing density and hindering depolymerization. With more cementitious material content, effective water–cement ratio is relatively decreased, subsequent hydration is limited, some slag powder does not participate in the reaction, reducing ASC toughness. [ABSTRACT FROM AUTHOR]

To reveal the expansion phenomenon and reaction characteristics of an aluminum particle filled polytetrafluoroethylene (PTFE/Al) reactive jet during the forming process, and to control the penetration and explosion coupling damage ability of the reactive jet, the temperature and density distribution of the reactive jet were investigated by combining numerical simulation and experimental study. Based on the platform of AUTODYN-3D code, the Smoothed Particle Hydrodynamics (SPH) algorithm was used to study the evolution behaviors and distribution regularity of the morphology, density, temperature, and velocity field during the formation process of the reactive composite jet. The reaction characteristic in the forming process was revealed by combining the distribution of the high-temperature zone in numerical simulation and the Differential Scanning Calorimeter/Thermo-Gravimetry (DSC/TG) experiment results. The results show that the distribution of the high-temperature zone of the reactive composite jet is mainly concentrated in the jet tip and the axial direction, and the reactive composite jet tip reacts first. Combining the density distribution in the numerical simulation and the pulsed X-ray experimental results, the forming behavior of the reactive composite jet was analyzed. The results show that the reactive composite jet has an obvious expansion effect, accompanied by a significant decrease in the overall density. [ABSTRACT FROM AUTHOR]

The incorporation of reactive material damage element technology in ammunition warheads is a research hotspot in the development of conventional ammunition. The research results are of great significance and military application value to promote the development of high-efficiency damage ammunition technology. In this paper, we aimed to understand the behavior of the reactive jet and its damage effect on a steel target by undertaking theoretical analysis, numerical simulation, and experimental research. We studied the influence of structural and material parameters on the shape of the reactive jet based on autodyn-2d finite element simulation software, and the formation behavior of the reactive jet was verified using a pulsed X-ray experiment. By studying the combined damage caused by the steel target penetrating and exploding the reactive jet, the influence of the structural and performance parameters, and the explosion height of the reactive jet liner on the damage effect to the steel target was studied. A static explosion experiment was carried out, and the optimal structural and performance parameters for the reactive material and explosion height of the reactive jet liner were obtained. [ABSTRACT FROM AUTHOR]

Recent studies have shown that the energy release capacity of Polytetrafluoroethylene (PTFE)/Al with Si, and CuO, respectively, is higher than that of PTFE/Al. PTFE/Al/Si/CuO reactive materials with four proportions of PTFE/Si were designed by the molding–sintering process to study the influence of different PTFE/Si mass ratios on energy release. A drop hammer was selected for igniting the specimens, and the high-speed camera and spectrometer systems were used to record the energy release process and the flame spectrum, respectively. The ignition height of the reactive material was obtained by fitting the relationship between the flame duration and the drop height. It was found that the ignition height of PTFE/Al/Si/CuO containing 20% PTFE/Si is 48.27 cm, which is the lowest compared to the ignition height of other Si/PTFE ratios of PTFE/Al/Si/CuO; the flame temperature was calculated from the flame spectrum. It was found that flame temperature changes little for the same reactive material at different drop heights. Compared with the flame temperature of PTFE/Al/Si/CuO with four mass ratios, it was found that the flame temperature of PTFE/Al/Si/CuO with 20% PTFE/Si is the highest, which is 2589 K. The results show that PTFE/Al/Si/CuO containing 20% PTFE/Si is easier to be ignited and has a stronger temperature destruction effect. [ABSTRACT FROM AUTHOR]

Dynamic response and fracture-induced initiation characteristics of aluminum particle filled polytetrafluoroethylene (PTFE/Al) reactive material was studied in two experimental configurations: (a) thin disks for compression and (b) hat-shaped specimens with predesigned shear bands of different widths for compression-shear, at elevated strain rates and temperatures. Compression stress-strain curves demonstrate typical elasto-plastic behavior with prominent strain hardening, strain rate strengthening, as well as thermal softening effects of the material. While growing oscillations and marked strength decrease due to shear band widths decrease observable on the shear stress-strain curves illustrate the localized shear induced adiabatic thermal effect and size effect of polymer materials. Post compression-shear to initiation phenomenon recorded by high-speed photography reveals the necessity of fracture process to initiation, apart from the intense shear work and loading rate effect. Employing the constitutive parameters determined at elevated strain rates and temperatures, 3D full size finite element modeling was performed. On the basis of a good agreement of the simulated and tested shear stress-strain curves for specimens of different shear band widths, a more direct insight into the deformation and stress evolution at the vicinity of the predesigned shear zones was analyzed and obtained. Unlabelled Image • Dynamic compression/shear response of PTFE/Al using hat-shaped specimen is investigated. • Size effect and adiabatic shear localization results in the four stages of shear stress-strain curves. • Post compression-shear to initiation reveals the fracture-induced initiation mechanism. • Direct insight into deformation and stress evolution in simulated shear bands is obtained numerically. [ABSTRACT FROM AUTHOR]

In this paper, the reaction characteristic of a novel reactive material, which introduced bismuth trioxide (Bi2O3) into traditional polytetrafluoroethylene/aluminum (PTFE/Al), is studied. The effect of Bi2O3 with different content and particle size on the reaction behaviors of PTFE/Al/Bi2O3 are investigated by drop-weight test and X-ray diffractometer (XRD), including impact sensitivity, energy release performance under a certain impact, and reaction mechanism. The experimental results show that the content of Bi2O3 increased from 0% to 35.616%, the characteristic drop height of impact sensitivity (H50) of PTFE/Al/Bi2O3 reactive materials decreased first and then increased, and the minimum H50 of all types of materials in the experiment is 0.74 times that of PTFE/Al, and the particle size of Bi2O3 affects the rate of H50 change with Bi2O3 content. Besides, with the increase of Bi2O3 content, both the reaction intensity and duration first increase and then decrease, and there is optimum content of Bi2O3 maximizing the reaction degree of the PTFE/Al/Bi2O3. Furthermore, a prediction model for the impact sensitivity of PTFE-based reactive material is developed. The main reaction products include AlF3, xBi2O3·Al2O3, and Bi. [ABSTRACT FROM AUTHOR]