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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]

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]

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]

AbstractThe reactive material-metal composite jet (RMM-CJ), exhibiting a dual penetration-enhancement effect is of growing concern. In the present study, the composite jets of reactive material-copper (RM–Cu), reactive material-titanium (RM–Ti), and reactive material-aluminum (RM–Al) impacting multi-spaced plates were studied experimentally and numerically. A comprehensive analysis of the damage effects was conducted based on experimental and simulation results. The results show that the damage area of each layer of plate is closely related to the mass distribution of reactive material. The relationship of the mass of each layer of reactive material with time is given, and the deflagration gain is quantified. The research results provide a useful reference for the design and optimization of reactive material-metal composite liners. [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]

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]

Composite concrete structures, commonly found in urban infrastructures, such as highways and runways, are pivotal research object in the protection field. To study the dynamic response of composite concrete structures subjected to reactive jet penetration coupled with an explosive effect, a full-scale damage experiment of composite structures under the action of 150 mm caliber shaped charges was performed, to derive the dynamic damage modes of different concrete thicknesses under the combined kinetic and chemical energy damage effects. The results indicated that under aluminum jet penetration, concrete layers exhibited minor funnel craters and penetration holes. However, concrete layers displayed a variety of damage modes, including central penetration holes, funnel craters, bulges, and radial/circumferential cracks when subjected to the PTFE/Al jet. The area of the funnel crater expanded as the thickness of the concrete increased, while the height of the bulge and the number of radial cracks decreased. The diameter of penetration holes increased by 76.9% and the area of funnel crater increased by 578% in comparison to Al jet penetration damage. A modified-RHT concrete model that reflected concrete tensile failure was established, utilizing AUTODYN. Segmented numerical simulations of damage behavior were performed using the FEM-SPH algorithm and a restart approach combined with reactive jet characteristics. The spatial distribution characteristic of the reactive jet and the relationship between kinetic penetration and explosion-enhanced damage were obtained by the simulation, which showed good concordance with the experimental results. This study provides important reference data and a theoretical basis for the design of composite concrete structures to resist penetration and explosion. [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]

In order to study the morphology characteristics of the PTFE/Al reactive shaped charge jet and the chemical reaction during the jet formation, PTFE/Al reactive liners with aluminum particle sizes of 5 μm and 100 μm were prepared. The parameters of the Johnson–Cook constitutive model of PTFE/Al reactive materials (RMs) were obtained through quasi-static compression experiments and SHPB (Split Hopkinson Pressure Bar) experiments. X-ray imaging technology was used to photograph the shape of reactive shaped charges jet at two different time points. The AUTODYN secondary development technology was used to simulate the jet formation, and the simulation results are compared with the experimental results. The results show that the simulation results are close to the experimental results, and the error is in the range of 4–8%. Through analysis, it is observed that the RMs reacted during the PTFE/Al reactive shaped charge jet formation, and due to the convergence of the inner layer of the liner during the jet formation, the chemical reaction of the jet is from inside to outside. Secondly, the particle size of aluminum powder has an influence on the chemical reaction and morphology of the jet. During the jet formation, there were fewer RMs reacted when the PTFE/Al reactive liners were prepared with 100 μm aluminum powder. Compared with 5 μm aluminum powder, when the aluminum powder is 100 μm, the morphology of the jet is more condensed, which is conducive to generating greater penetration depth. [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]

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]

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]

Many scholars have used experimental research methods to conduct extensive research on the impact energy release behavior of Polytetrafluoroethylene(PTFE)/Al reactive materials. However, in numerical simulation, PTFE/Al still lacks the calculation parameters of impact energy release behavior. In order to obtain the simulation parameters of PTFE/Al impact ignition, the Hill mixture law was used to calculate the material parameters of PTFE/Al (mass ratio 73.5/26.5), and according to the Hugoniot curve of PTFE/Al and the γ state equation, the JWL equation of state of a PTFE/Al unreacted substance and reaction product was fitted with a genetic algorithm. According to the PTFE/Al impact energy release experiment, the parameters of the PTFE/Al chemical kinetic equation were determined, and the parameters of the trinomial reaction rate equation were fitted. The obtained parameters were used in the simulation calculation in LS-dyna to predict the damage of the aluminum target plate under the impact of the PTFE/Al reactive fragments. [ABSTRACT FROM AUTHOR]

In this study, the static and dynamic mechanical behaviors of four types of PTFE/Al/W reactive materials with different component mass ratios were studied. The mechanical properties of reactive materials at elevated strain rates and temperatures were tested by quasi‐static compression and Split Hopkinson Pressure Bar (SHPB). Parametric study on material properties was carried out, and the Johnson‐Cook constitutive constants were well determined. Based on the good agreement between the predicted and tested constitutive response, a systematic comparison of the static and dynamic behaviors, as well as the comprehensive stress‐strain relationships were conducted, regarding the strain rate and temperature effect. Microscopic fractographic analysis of the tested samples reveals the localized thermal softening effects and fiber network formation phenomenon of the matrix, which dominate the overall mechanical response of the four types of PTFE/Al/W reactive materials, and contribute to the elasto‐plastic property, strain hardening, strain rate strengthening and thermal softening effects. [ABSTRACT FROM AUTHOR]

This paper begins with experiments to investigate the behind‐target damage effects on sandwich‐like plates subjected to reactive liner shaped charge jet. Sandwich‐like plates, consisting of triple spaced aluminum plates filled with flame‐retardant foams, are placed under a steel target. The reactive liner shaped charge is initiated at a stand‐off of 1.0 CD, producing a reactive jet to perforate the steel target and then cause behind‐target damage effects on sandwich‐like plates. The experimental results show there is an unusual rupturing effect on sandwich‐like plates, which strongly depends upon the steel target thickness. Generally, the rupturing effects on sandwich‐like plates increase gradually with the steel target thickness decreasing from 60 mm to 40 mm. Then, the interaction mechanism between the reactive jet and target is discussed in three phases. The formation phase shows an expansion behavior of reactive jet, leading to the jet density less than the initial density. The penetration phase results in central holes on aluminum plates and provides a precondition for cracks. Then, the deflagration reaction phase causes a field of high temperature and high pressure inside the sandwich‐like plates, which enlarges the kinetic energy‐induced pre‐perforations and thereby causes the unusual rupturing effects. Finally, an analytical model for the rupturing damage to aluminum plate is developed and the relevant parameter is obtained approximately. [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]

Abstract: Physical experiments were performed to investigate the enhanced lethality of reactive materials (RMs) shaped charge liner against concrete target. The results show that the shaped charge with RMs liner left a funnel shaped hole on the pure concrete target front surfaces, whereas the Cu liner just left a slender penetration hole and produced less damage in comparison. The damage events were recorded by high‐speed photography with the frame rate up to 10,000 frames/s, and the results indicate that deflagration reaction of RMs has occurred inside the target after the detonation of main charge. By comparison of damage effects between RMs and inert Cu liners, we conclude that the gaseous products of the deflagration are the main inducement of catastrophic damage. For multi‐layered concrete targets, a cavity inside the target and several cracks on the targets front surfaces were formed, and the formation mechanisms are deeply discussed in this paper. Based on the isentropic expansion and crack growth theories, the computational formula for crack length was developed, and the influences of the mass of RMs and initiation depth on crack effects are achieved. [ABSTRACT FROM AUTHOR]

Reactive materials bring the dramatically enhanced lethality by means of the combined defeat mechanisms of impact kinetic energy and chemical energy release. This paper presents such an investigation on these reactive materials for the enhanced initiation behavior of covered explosives. First, a simple initiation process comparison between the inert metal and reactive material projectiles impacting covered explosives is described. Then high velocity ballistic impact experiments, which include both reactive material and tungsten alloy projectiles with mass matched against covered explosives, are conducted to investigate and compare the initiation behavior of covered explosives. Finally, theoretical analysis and discussions about contributions of both kinetic energy-to-initiation and chemical energy-to-initiation mechanisms to the enhanced initiation behavior of covered explosives impacted by reactive materials are presented. [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]

The behind-plate overpressure effect by a reactive material projectile with a density of 7.7 g cm−3 was investigated by ballistic impact and sealed chamber tests. The reactive projectile was launched onto the initially sealed test chamber with a 2024-T3 aluminum cover plate with a thickness of 3 mm, 6 mm, and 10 mm, respectively. Moreover, the overpressure signals in the test chamber were recorded by a pressure sensor and a data acquisition system. The experimental results show that the behind-plate overpressure effect is significantly influenced by plate thickness and impact velocity. For a given plate thickness, the peak overpressure in the test chamber shows an increasing trend with increase of impact velocity. However, for a given impact velocity, when impacting the 6 mm thick aluminum plate, the peak overpressure measured and the impulse delivered to chamber are higher than the values recorded for the 3 mm and 10 mm thick aluminum plates. As such, it is inferred that there is an optimum plate thickness to maximize the behind-plate overpressure effect by reactive projectile. [ABSTRACT FROM AUTHOR]

The application of reactive materials on shaped charge liners has received much attention. Herein, the demolition mechanism and behavior of reactive materials based shaped charge liner are investigated by experiment, numerical simulation, and theoretical analysis. Three reactive shaped charge liners, composed of a mixture of Al/PTFE (26.5/73.5 wt-%) powders, are fabricated by pressing and sintering. The damage effects of the multi-layered target against reactive materials based shaped charge are investigated. The results show that the reactive liners create excellent collateral damage due to the release of chemical energy contained in reactive materials. An Eulerian computational model is developed to investigate penetration behavior of the reactive jet formed by shaped charge liner. In addition, a theoretical model based on cavity expansion is derived to predict the initiated location of reactive materials. Comprehensive analysis indicates that the TNT equivalence factor for these powder mixtures used in this work is 3.41-7.77 and that the self-delay time is about 0.8 ms. This work will provide guidance and reference for the design of reactive shaped charge liner. [ABSTRACT FROM AUTHOR]

Reactive material lining is an efficient damage enhancement technology that incorporates the defeat mechanisms of kinetic energy and chemical energy. The liners are fabricated by cold isostatically pressing at a pressure of 250 MPa. In this paper, the formation behaviors of jet with the polymer-based reactive material liner are investigated by numerical simulation and X-ray photographs. The corresponding simulations of jet formation are presented, and the results agree well with experimental ones. They show that the reactive material liner can shape almost continuous and straight jet. Compared with the conventional copper liner, the reactive material liner can shape jet in a shorter time, but the jet break easily and lose stability due to its poor ductility. Although the penetration depth is sacrificed slightly when penetrating steel target, the reactive material liner produce a significantly enlarged hole-diameter. [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]

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 formation process of reactive materials shaped charge is investigated by X-ray photographs and numerical simulation. In order to study the formation process, a trans-scale discretization method is proposed. A two-dimensional finite element model of shaped charge and reactive material liner is established and the jet formation process, granule size difference induced particle dispersion and granule distribution induced jet particle distribution are analyzed based on Autodyn-2D platform and Euler solver. The result shows that, under shock loading of shaped charge, the Al particle content decreases from the end to the tip of the jet, and increases as the particle size decreases. Besides, the quantity of Al particles at the bottom part of the liner has more prominent influence on the jet head density than that in the other parts, and the Al particle content in the high-speed section of jet shows inversely proportional relationship to the ratio of the particle quantity in the top area to that in the bottom area of liner. [ABSTRACT FROM AUTHOR]

Drop-weight tests were conducted to investigate the impact-initiation sensitivity of high-temperature PTFE-Al-W reactive materials. The test results show that the impact-initiation sensitivity of the materials more than doubles with increasing the sample temperature from 25 to 350 °C. Combined with the impact-induced initiation process recorded by high-speed video and the difference between reacted and unreacted residues, the crack-induced initiation mechanism was revealed. The rapid propagation of crack provides a high-temperature and aerobic environment where Al reacts violently to PTFE, which induces the initiation. Moreover, the influence of sample temperature on the sensitivity was discussed and analyzed. The analysis results indicate that the sensitivity shows a temperature interval effect, and 127 and 327 °C are the interval boundaries where the sensitivity changes significantly. The sensitivity may leaps at 127 °C and increases more rapidly in the temperature interval from 127 to 327 °C, but hardly changes after the temperature reaches 327 °C. [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]