Explosive Heat Research Articles

Study of microstructure evolution in the aluminum‒magnesium alloy AlMg6 after explosive welding and heat treatment

Study of microstructure evolution in the aluminum‒magnesium alloy AlMg6 after explosive welding and heat treatment

Study of Structure Formation in Multilayer Composite Material AA1070-AlMg6-AA1070-Titanium (VT1-0)-08Cr18Ni10Ti Steel after Explosive Welding and Heat Treatment

Multilayer composite materials, consisting of layers of aluminum alloy and steel, are used in the manufacturing of large engineering structures, including in the shipbuilding and railcar industries. Due to the different properties of aluminum alloys and steels, it is difficult to achieve high-strength joints by conventional welding. Therefore, these joints are produced by explosive welding. In the present work, the structure of a multilayer material, AA1070-AlMg6-AA1070 (aluminum alloys)-VT1-0-08Cr18Ni10Ti (steel), was investigated after explosive welding and heat treatments were performed under different conditions. The microstructure of the AlMg6 layer at the AlMg6-AA1070 interface consists of shaped anisotropic grains extending along the weld interface. The AA1070 layer is enriched with magnesium due to its diffusive influx from AlMg6. In the AlMg6 and VT1-0 layers, adiabatic shear bands are found that start at the weld interface and propagate deep into the material. The optimal temperature for the heat treatment is 450–500 °C, as internal stresses are reduced at this temperature and the grain structure of the AlMg6 layer is not coarse. Tear strength testing revealed that the tear strength of the composite material after explosive welding was 130 ± 10 MPa, which exceeded the strength of the AA1070 alloy.

Theoretical exploration of the stabilities and detonation parameters of nitro-substituted 1H-benzotriazole.

The nitro group was introduced into the nitrogen heterocycle of 1H-benzotriazole to design a total of 31 derivatives. To estimate the thermal stability of these derivatives, the heat of formation (HOF) is calculated based on the isodesmic reaction. The bond dissociation energy (BDE) was also predicted based on the homolytic reaction to further evaluate the dynamic stability. To evaluate the possibility of utilizing as high energy density compounds (HEDCs), the detonation parameters including the detonation pressure (P), detonation velocity (D), and explosive heat (Q) are predicted by taking advantage of the Kamlet-Jacobs empirical equation. To measure the sensitivity to impact, both the characteristic height (H50) and free space in crystal (∆V) are considered in this paper. Based on our calculations, D-series and E are found to be the candidates for HEDCs. The Gaussian 09 software package was used in this paper. The B3PW91 hybrid function with the 6-311 + G(d,p) basis set was chosen to perform the structural optimization, frequency analysis, heat of formation, and bond dissociation energy. The detonation parameters were calculated following the Kamlet-Jacobs equation.

Fabrication and energy release study of metastable intermolecular composite microspheres with enhanced combustion performance

Metastable intermolecular composites (MICs) are often used in military and aerospace applications because of their high energy density. However, the traditional preparation methods are either complicated and unsafe, or the prepared composites have incomplete combustion and low energy release rates. In this paper, a series of aluminum/metal oxide/nitrocellulose (AMxN) composite microspheres were prepared by spray drying technique. The field emission scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) results show that the prepared AMxN composite microspheres have regular morphology and uniform particle size, and nitrocellulose (NC) is successfully coated between fuel (Al) and oxidizers (CuO, MoO3, and Bi2O3). The thermal reactivity, energy, and combustion properties of AMxN were investigated and compared with physically mixed aluminum/metal oxide (AMx). The explosion heat of AMxN is higher than AMx, while the thermal reaction exothermic peak temperature is lower. Among them, the composite containing copper oxide has the highest explosive heat value (5034 J/g), and the composite containing bismuth oxide has the shortest burning time (2.8 ms). These results prove that NC as a binder shortens the reaction distance between the oxidizer and the fuel in the presence of spray drying. Different oxidizers can modulate the energy release rate of AMxN composites, which is beneficial for applying MICs in energetic materials.

Investigation of the suppression effect of inert dust on the pressure characteristics of gas coal dust explosion

The suppression effect of inert powder on gas-induced suspension coal dust explosions was investigated using a semi-closed pipeline experimental platform. The shock wave overpressure propagation characteristics of gas explosions with different concentrations of mixed dust (calcium carbonate and coal dust) were measured and analyzed. The suppression mechanism of inert powder on the explosion process was also discussed. The results indicate that when the coal dust concentration is 200g/m?, the peak overpressure of the explosion decreases gradually with increasing inert powder concentration, and the peak overpressure ratio in the pipeline shows a decreasing-increasing trend; the acceleration of the explosion pressure reduces with increasing mixed dust concentration, and when high concentration of mixed dust is involved in the explosion, the acceleration of the explosion pressure is lower than that when only coal dust is involved; The inhibitory effect of calcium carbonate on dust explosion increased linearly with its concentration when the ratio of inert dust to coal dust was 1:2.; Inert powder mainly suppresses the explosive power by physical heat absorption and reducing heat exchange efficiency. The experimental results established the theoretical basis for inert dust suppressing coal dust participation in explosions, and have reference significance for formulating mine explosion suppression measures.

Theoretical study about the thermal stability and detonation performance of the nitro-substituted derivatives of 4-(1H-1,2,4-triazol-1-yl) pyrimidine

The nitro groups are introduced into 4-(1H-1,2,4-triazol-1-yl) pyrimidine to substitute the hydrogen atoms successively, through which a total of 31 derivatives are constructed to look for high energy density compounds (HEDCs). To probe the thermal stabilities, the heats of formation (HOFs) are calculated by using the G3MP2 method. To explore the dynamic stability, the natural bond orbital (NBO) analysis is performed to confirm the trigger bond, for which the bond dissociation energy is calculated using the B3PW91 method with the 6-311 + G(d,p) basis set. Furthermore, the detonation velocity (D), the detonation pressure (P), the molecular density (ρ), the explosive heat (Q), and character height (H50) are also predicted. Based on our calculation, it is confirmed that D1, D2, D5, and E are potential high-energy-density compounds with sufficient stability and excellent detonation performance.

Structures, cold pressure lines, and electronic properties of cubic Al2O and AlO: First-principles calculations.

Aluminized explosive has attracted more and more attention in recent years because of its high explosive heat and high power. Al2O and AlO are indispensable aluminum oxides in the explosion process of aluminized explosives. The study of the physical properties of solid Al2O and AlO under pressure may play an important role in the understanding of the explosion mechanism of aluminized explosives. CONTEXT: The structures, cold-pressed lines and electronic properties of cubic Al2O and AlO are calculated and analyzed based on first-principles calculation in this paper. The optimized structures of Al2O and AlO are in good agreement with those previously studied. The cold pressure line shows that the specific volumes of Al2O and AlO decrease with increasing pressure. The peak values and peak positions of density of state of Al2O and AlO change greatly under pressure. METHODS: The CASTEP code was used to execute these calculations throughout the present work, where the plane-wave basis set and norm conserving pseudopotential were employed.

Development and Performance Analysis of an Atomic Layer Thermopile Sensor for Composite Heat Flux Testing in an Explosive Environment

Traditional contact heat flux sensors suffer from a lack of dynamic performance, and existing non-contact optical heat measurement equipment fails to detect convective heat transfer effectively. This limitation precludes the effective testing of composite heat flux in explosive fields. This study introduces an ultra-responsive atomic layer thermopile (ALTP) heat flux sensor, developed and employed for the first time, to evaluate the transient heat flux associated with thermobaric explosions. Measurements reveal that the ALTP sensor’s temporal resolution surpasses that of the thermal resistance thin film heat flux sensor (TFHF), attaining a spectral response time of 10 μs under pulsed laser irradiation. Beyond these radiation-based tests, the present work also conducted novel simulation analyses of high-temperature jet impacts using COMSOL software. Static simulation discovered that fluid velocity significantly influences ALTP’s sensitivity, resulting in an error of 71%. Conversely, dynamic simulation demonstrated that an increase in fluid velocity reduces the ALTP’s time constant, whereas other factors such as fluid temperature exert minimal impact on its dynamic characteristics. This confirms that the simulation model compensates for the cost and accuracy deficiencies of convection heating tests. It also provides a new way to analyze the error of explosive heat flux measurement caused by sensitivity fluctuation and insufficient dynamic performance. In thermobaric explosive trials, the maximum heat fluxes recorded were 202 kW/m2 in semi-enclosed environments and 526 kW/m2 in open environments. A distinctive double-wave phenomenon was evident in the test curve. By a fast-response thermocouple, the study was able to differentiate between radiation and convective heat flux in the explosion field. The findings substantiate that the ALTP sensor amalgamates the benefits of optical thermal measurement tools with those of traditional contact heat flux sensors, thereby facilitating composite heat flux measurements in the challenging conditions of an explosive field.

Microstructure Evolution and Growth of Interfacial Intermetallic Compounds in NiCr/Ti Alloy Laminated Composite after Explosive Welding and Heat Treatment

The paper considers the issues of interaction of the molten metal at the interface of explosively welded NiCr/titanium alloy laminated composites with the reaction zone formed during heat treatment, as well as the features of its destruction after welding. It was established that the molten metal is a heterogeneous mixture based on Ni(Cr,Ti) and Ti(Ni,Al) solid solutions and NiTi and Ni3Ti intermetallic compounds. The estimated existence time of molten metal areas in the liquid state was ~10−8–10−11 s. The obtained values are comparable with the time of the unloading wave arrival at the contact surface, which is the reason for the presence of fracture areas in the form of detachments on the fracture surface. Continuous nanometer-size interlayers with an amorphous structure, due to the ultra-high cooling rate of the liquid melt, induce viscous destruction of the interface. Heat treatment at temperatures of 700 and 850 °C led to the formation of a layered reaction zone at the NiCr/Ti boundary, consisting of interlayers of solid solutions based on Ti2Ni, TiNi, and TiNi3 intermetallic compounds, as well as inclusions of a Cr(Ti) solid solution. The diffusion flow gradient was predominantly directed into the titanium alloy.

Research on the Performance of Deterred-coating DIANP Gun Propellant

Deterred-coating DIANP gun propellant was prepared by the two-step process called “polymer composite materials deterring and energetic composite materials coating”. The performance of energy and static combustion of deterred-coating DIANP gun propellant was investigated by explosive heat and closed-bomb test. The results show that compared with DIANP gun propellant, the energy of deterred-coating DIANP gun propellant decreased by only about 3.2%, but it had better combustion progressivity and low temperature sensitivity effect. The combustion progressivity of deterred-coating DIANP gun propellant was improved by increasing the content of deterring and coating materials.

Suppression effects of ABC powder on explosion characteristics of hybrid C2H4/polyethylene dust

In order to analyze the suppression effects and mechanisms of ABC powder on ethylene gas (C2H4)/polyethylene (PE) hybrid explosion, to explore the suppression characteristics of gas-solid two-phase explosion, the 20-L apparatus are used for the test of the explosion overpressure. The results show that when the volume fraction of C2H4 is 3%, the concentration of ABC powder required to completely inhibit the explosion of 300 g/m3 PE dust increases from 200 g/m3 to 1200 g/m3. When increasing the volume fraction of ethylene to 5% and 7%, the explosion overpressure reduction in the mixture is 40.68% and 28.59%. The results of thermal analysis show that the addition of ABC powder improves the thermal stability of PE particle. Through the physical effects of heat absorption, oxygen insulation, and thermal transmission weakened and the chemical effect of eliminating explosive radicals, ABC powder reduces the rate of explosive chain reaction and heat release rate, thus producing an effective inhibition effect. But C2H4 will induce the explosion process of the mixture from two-phase combustion to homogeneous combustion to promote the explosion, and its effect is opposite to that of ABC powder pyrolysis in the system, which makes the explosion of mixed system more difficult to be suppressed.

Effects of 2CL-20/HMX cocrystals on the thermal decomposition behavior and combustion properties of polyether solid propellants

Herein, the effects of cocrystals of two nitroamine explosives, namely hexanitrohexaazaisowurtzitane (CL-20) and 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX), which are denoted as CHC, on the combustion properties, heat release, and safety profiles of polyether solid propellants were systematically analyzed. The peak decomposition temperature of CHC was found to be 244.8 °C, which is lower than those of its component CL-20 and HMX. However, the thermal stability of CHC was similar to that of CL-20, and the thermal decomposition behavior of CHC was significantly different from that of a physical mixture of CL-20 and HMX. In addition, similar to CL-20, CHC was not completely decomposed upon heating, despite the decomposition activation energy of CHC (322.7 kJ·mol−1) being similar to that of HMX (322.4 kJ·mol−1). In contrast, the thermal decomposition behaviors of CHC-based propellants differed from those of solid propellants that were based on physical mixtures of CL-20 and HMX. During thermal decomposition, CHC did not decompose into CL-20 and HMX, and the heat released from the CHC-based propellants was more concentrated than that released from the other propellant mixture examined. Furthermore, the rate of combustion of CHC-based propellants fell between those of the CL-20- and HMX-based propellants at all the tested pressures. The pressure exponents of combustion rates of the examined CHC-based propellants were slightly lower than those of the CL-20- and HMX-based propellants, and the combustion rates and their corresponding pressure exponents decreased with a decrease in the CHC particle size. Moreover, the explosive heat of CHC-based propellant was between those of the CL-20-based and HMX-based propellants, and similar to that of a CL-20/HMX mixture-based propellant. Finally, the safety performance of CHC-based propellant was almost identical to that of the CL-20/HMX mixture.

Evaluation of the safety parameters for a permitted explosive type emulsion

When preparing a permitted explosive recipe an energy or an explosive heat is considered, which should ensure the detonability of the system and at the same time a power that satisfies the purpose for which it will be used, under the conditions of firedamp hazardous mines. The safety parameters for the explosive charges used in the firedamp hazardous mines are decisive, in order to ensure the safety and health requirements at work together with the efficient performance of the blasting operation. The permitted explosive type emulsion is recommended to be used in underground mines, open pit mines as a special methane explosive and can be used where a coal dust and/or methane explosion hazard exists can be loaded into dry and wet blasting holes and it can be used for mechanical loading. The permitted explosive type emulsion is a Detonator-sensitive explosives that can be reliably initiated in an unconfined state by a No. 8 strength detonator it have safety handling characteristics because of the relatively low sensitivity to friction, shock and impact. Technological changes due to the change of suppliers of certified explosives for civil use for underground use in the firedamp hazardous mines, involve reassessing the safety and efficiency of the loads made with these products, which have not been tested and evaluated for the conditions from the Jiu Valley mines.

A Hotspot Model for PBX Explosive Charge Ignition in a Launch Environment.

ABSTRACT The research of explosive ignition mechanisms in the launch environment is significant to determine the launch safety of explosive charge. Based on the two-phase flow theory, the internal ballistic process and the projectile base pressures are calculated accurately. The stress history of PBX explosive during the 155 mm howitzer launching process is obtained based on the finite element method, and then the 1D hollow sphere pore-collapse model considering explosive chemical reaction, heat conduction, phase transition, and viscoplastic deformation processes can be developed, to describe the hot spot formation in explosive charge. Finally, a quantitative determination method with initial porosity as the index for explosive ignition is proposed, contributing to the launch safety determination and performance evaluation of explosive change.

Theoretical exploration about the thermal stability and detonation properties of nitro-substituted hypoxanthine

Nitro-substituted derivatives of hypoxanthine are designed by substituting the hydrogen atoms by nitro groups. The heats of formation (HOF) are calculated at the G3MP2 level to confirm the thermal stability. Also, the bond dissociation energy (BDE) accompanied by the bond order is calculated at the same level to explore kinetic stability. To evaluate the potential application as high-energy density materials, the explosive heat, the molecular density, the detonation pressure, and detonation velocity are estimated by using the Kamlet-Jacobs (K-J) equation. Furthermore, the molecular sensitivities are considered by calculating the character height (H50) and the amount of free space per molecule in the crystal lattice (ΔV). Based on our calculations, the trinitro-substituted hypoxanthine (C) is screened out as the potential high-energy density compounds for further study.

Dynamic characteristics analysis of an infrared thin skin calorimeter for explosive heat flux measurements

In order to meet the requirements of explosive heat flux measurements, a series of novel improvements for the thin skin calorimeter are proposed in this paper. An infrared thermopile is used in the calorimeter to eliminate the heat dissipation effect caused by the thermocouple firstly. Then a non-overshoot model of high order terms is established by a novel processing method of the temporal derivative. Next, an order-reduction calibration method is used to obtain the coefficients of the non-overshoot model by a narrow-pulse-laser. Finally, an explosive experiment is made to verify the performance of the calorimeter. The calibration results show that dynamic characteristics of the calorimeter are gradually improved with the increase of the model order and the biggest improvement is obtained at the 2nd order. In the experiment, the peak time of the 2nd order model decreases by 54.6% and the peak value increases by 51.3%, compared with the 1st order model.

Experimental research on dynamic concentration distribution for combustible dust based on ultrasonic-electric hybrid detection

The concentration distribution of combustible dust determines thermal intensity distribution during an explosion. Current measurements for dust concentration have their particular limitations. Targeting this, we proposed an “ultrasonic-electric” hybrid detection system and a fusion model. We deployed 12 of the ultrasonic-electric hybrid systems in orthogonal arrays to comprehensively observe the clouds. First, the ultrasonic-electric hybrid detection systems obtained concentration data in real time, and those data were calculated by fusion model. Then, the clouds and their concentrations changing with time were depicted. We analyzed those trends and found certain patterns in them. Our approach can provide a fast, accurate way to detect concentrations of dynamic and complex dust. Finally, the corresponding relationship between the dust concentration distribution and its explosive heat intensity distribution is obtained. The results show that the thermal distribution of combustible dust at a concentration of 20-120 g/m3 is proportional to the concentration. This is important for preventing dust explosions and reducing the thermal intensity of explosions.

Thermal stability and detonation characters of nitro-substituted derivatives of pyrazole

High-energy-density compounds are designed successively by substituting the hydrogen atoms of 1H-pyrazole by the nitro group. The thermal stabilities are explored by the calculations of the heat of formation, bond orders, and bond dissociation energy at the B3PW91/6-311 + G(d,p) level. To evaluate the potential application as high-energy-density compounds, the molecular density (ρ), explosive heat (Q), the detonation velocity and detonation pressure are evaluated by using the empirical Kamlet-Jacobs equation. Based on our calculations, five molecules (3,4,5-trinitro-1H-pyrazole, 1,4,5-trinitro-1H-pyrazole, 1,3,5-trinitro-1H-pyrazole, 1,3,4-trinitro-1H-pyrazole, 1,3,4,5-tetranitro-1H-pyrazole) reached the balance between the stability and detonation characters and can be regarded as the potential high-energy-density compounds.

Assessing an experimental approach for chemical explosive mode and heat release rate using DNS data

Obtaining information about burning characteristics and flame structures by analyzing experimental data is an important issue for understanding combustion processes and pursuing combustion modeling approaches. It has been shown that Raman/Rayleigh measurements of major species and temperature can be used to approximate the local heat release rate and the chemical explosive mode, and that these results are sufficiently accurate for a qualitative assessment of the relative importance of different heat release zones within the same overall flame structure in laminar and mildly turbulent partially premixed flames [1,2]. The present study uses data from direct numerical simulation (DNS) to extend and quantify the understanding of the approximation method with respect to premixed and stratified-premixed flames with significant turbulence–chemistry interaction (high Karlovitz number). The accuracy of the approximation procedure is assessed as previously applied, using just major species and temperature, as well as with the OH radical included as an additional experimentally accessible species. The accuracy of the local chemical explosive mode and the local heat release rate results from the approximation are significantly improved with OH included, yielding quantitative agreement with the DNS results. Further, a global sensitivity analysis is applied to identify the sensitivity of the heat release rate and chemical explosive mode to experimental uncertainties imprinted upon the DNS data prior to the approximation procedure.

Preparation of Bi2O3/Al Core-Shell Energetic Composite by Two-Step Ball Milling Method and Its Application in Solid Propellant.

In this article, Bi2O3/Al high-density energetic composites with a core-shell structure were prepared by a two-step ball milling method using a common planetary ball milling instrument, and their morphology, structure, and properties were characterized in detail. Through a reasonable ratio design and optimization of the ball milling conditions, the density of the Bi2O3/Al core-shell energetic composite is increased by about 11.3% compared to that of the physical mixed sample under the same conditions. The DSC (Differential Scanning Calorimetry) test also showed that the exothermic quantity of the thermite reaction of the energetic composite reached 2112.21 J/g, which is very close to the theoretical exothermic quantity. The effect of Bi2O3/Al core-shell energetic composite on the energy performance of insensitive HTPE propellant was further studied. The theoretical calculation results showed that replacing the partial Al with Bi2O3/Al core-shell energetic composite can make the density of propellant reach 2.056 g/cm3, and the density specific impulse reach 502.3 s·g/cm3, which is significantly higher than the density and density specific impulse of the conventional composite solid propellant. The thermal test showed that the explosive heat of the HTPE (Hydroxyl terminated polyether) propellant also increased with the increase of the content of Bi2O3/Al core-shell energetic composite.