Multi-walled carbon nanotubes (MWCNTs) were synthesized via the detonation of methane and oxygen as precursors and ferrocene as catalyst in a sealed stainless steel pressure vessel.Then the MWCNTs were characterized by X-ray diffraction (XRD), transmission electron microscopy and Raman spectroscopy.The results indicate that MWCNTs present appearance of entangled morphologies with outer diameters of 20-50 nm and lengths up to several microns, which have an excellent tubular structure and a relatively high graphitization degree; A small number of iron (Fe) nanoparticles remaining in the MWCNTs consist of Fe₃C, which results from the continuous supply of carbon source and iron catalyst.XRD analysis shows that, after the detonation reaction, the catalyst is broken down and reduced to metal simple substance.Through the experimental results and theoretical analysis, we propose the formation mechanism of gas detonation synthesis of carbon nanotubes.

Carbon microspheres prepared using the chemical vapor deposition method were treated under high-pressure and high-temperature conditions of about 8 GPa and 1 600 ℃.Based on the volume variation of diamond and molybdenum with the pressure and temperature, we designed and optimized the temperature-pressure path for sample treatments, thereby reducing the residual stress caused by the difference between the diamond's and the molybdenum's elastic modulus and thermal expansion.The Raman spectrum show that the samples have an obvious 1 332 cm^-1 diamond characteristic peak, and the high-temperature and high-pressure treatments effectively eliminate the trans-polyacetylene in the initial diamond-like carbon microsphere.The scanning electron microscope results show that the samples exhibit good sphericity, with an average diameter of 2 mm, the diamond-like film surface has an average grain size of 100 nm, and the film thickness is about 20 μm.The atomic force microscope test results show that the surface roughness is 647 nm.

The research of the effect of rapid compression within milliseconds on materials is still in its initial stage.Therefore, it is necessary to improve the rapid compression experimental technology and carry out in-depth research on rapid compression process and its application in materials science.In the present review, we discuss 4 kinds of experimental techniques developed to produce the rapid compression within milliseconds, and summarize their applications in material science, including preparing amorphous materials, measuring Grüneisen and W-J parameters, and studying the transformation kinetics.

To assess the suitability of 47Zr45Ti5Al3V alloy used in the future spacecraft in a space debris environment, we performed single and repeated hypervelocity impact experiments on a laser driven mini-flyer system.The crater depth in the recovered target was measured by a surface profile meter.The relationship between the crater depth and the velocity of flyer and the relevance of the crater depth and impact frequency were obtained.We also studied the microstructural changes and micro-damage behaviors of 47Zr45Ti5Al3V alloy using a scanning electron microscope and a transmission electron microscope.The results show that there are no micro-cracks, micro-voids, adiabatic shear bands or dynamic recrystallization in the region adjacent to the crater.In addition, the X-ray diffraction pattern of the bottom of the crater reveals that α and β phases coexist and α→β phase transition occurs, suggesting that the 47Zr45Ti5Al3V alloy exhibits good characteristics of structural stability and mechanical properties after hypervelocity impact, and it is a potential structural material for improving protection against orbital debris impacts on the future spacecraft.

To find out about the effect of hardness on the dynamic behavior and the damage parameters of 30CrMnSiNi2A steel, we investigated the quasi-static and dynamic mechanical properties of different steel alloys with the hardness of 31HRC, 36HRC, 45HRC and 55HRC using a universal material testing machine and a split Hopkinson pressure bar (SHPB).Based on the relationship among the yield strength, the strain rate and the equivalent plastic strain, we determined the parameters of Johnson-Cook constitutive model of 30CrMnSiNi2A steel with different hardnesses.Furthermore, we obtained the parameters of Johnson-Cook failure model for 30CrMnSiNi2A steel by the relationship among the failure strain, the stress triaxiality and the strain rate, and summarized the remarkable influence of the hardness on the parameters of Johnson-Cook constitutive model and failure model of 30CrMnSiNi2A steel.The results show that, as the hardness of 30CrMnSiNi2A steel increases, its plasticity and strain rate sensitivity decreases, but its brittleness increases.

From a micromechanical point of view, concrete was considered as a three-phase composite composed of cement mortar, coarse aggregate and interface transition zone (ITZ) between them.In order to study the influence of ITZ on the dynamic mechanical behavior of concrete, we designed a two dimensional circular coarse aggregate random distribution program to simulate the dynamic failure process of concrete with different ITZ sizes, and analyzed the influences of the ITZ size, the specimen size, and the particle size and the volume fraction of coarse aggregate on the load-carrying capacity of concrete.Numerical simulation showed that the concrete with different ITZ sizes has an obvious size effect.The load-carrying capacity of the concrete with different ITZ sizes decreases with the size of ITZ.When the ITZ size and the particle size of the coarse aggregate are kept unchanged, the load-carrying capacity of the concrete increases at first and then decreases with the volume fraction of the coarse aggregate; when the minimum particle diameter of the coarse aggregate and the ITZ size are kept constant, the load-carrying capacity of the concrete increases at first and then decreases with the increase of the maximum particle diameter of the coarse aggregate.

Plain concrete exhibits a significant strain rate hardening effect, and the relationship between the dynamic increase factor (DIF) and the corresponding strain rate at high strain rates is obviously different from that at low strain rates.In this paper, we collected and examined a large number of dynamic compression test data of plain concrete from the public literatures in the past 30 years.Based on the comparison among these data, we analyzed the relationship between the DIF and the strain rate in different strain rate regions and then investigated the influences of the static compressive strength on the DIF of compressive strength.Finally, we proposed a new relation between the DIF and the compressive strain rate of concrete.The results show that the DIF of compressive strength of the concrete increases linearly approximately with the increase of the strain rate; there are three different regions in the DIF of the compressive strength versus the strain rate curve, and the slope of the curve in the high strain rate region is the highest, but there is no notable relationship between the slope and the quasi-static compressive strength.

The Russian pine is widely used in packaging, transportation and penetration test.In this paper, we studied the stress-strain relationship and the failure mode of the Russian pine under quasi-static loading.The results show that the deformations of the pine in the radial and tangential directions undergo three phases:elastic deformation, plastic deformation and densification, and in the axial direction the pine undergoes small plastic deformations and damages when the yield limit is reached.The failure mode of the tangential and radial directions is mainly dissociated along the fiber direction, and the axial failure mode is dominated by the kink crack.Furthermore, we carried out high strain-rate dynamic compression tests of the Russian pine at the strain rates ranging from 500 s^-1 to 5 000 s^-1 using the split Hopkinson pressure bar system.The results show that the initial yield stress in the axial direction is more sensitive than that in the tangential and radial directions.The radial platform stress increases more rapidly with the strain rate than the tangential platform stress.The energy absorption capacity along the tangential and radial directions increases gradually as the strain rate increases, while it decreases gradually along the axial direction.The failure mode under dynamic loading is highly similar to that under the quasi-static loading.

After validating our hydrodynamics program and damage model with the corresponding experimental data, we carried out numerical simulation study on the damage and spall mechanism of Sn under the explosive detonation loading.The numerical results show that the damage in Sn sample is related to the loading intensity, the wave profile and the sample size; the initial microstructure of the material will act on the critical fracture damage and then affect the damage and spall in the sample, and the damage decreases with the increase of the critical fracture damage.Moreover, the comparison of the numerical results with the experimental results on the tension and compression damages indicates that the tension damage plays a decisive role in material damage.

To quantitatively study the air blast wave field characteristics of the explosive charge moving at different velocities, we carried out simulations using AUTODYN software.The simulation results show that the charge velocity exerts great influence on the time-space distribution of the blast wave field.At the initial stage of the explosion, the moving speed and the displacement of the blast wave field are positively correlated with the charge velocity.The space distribution of the dynamic blast wave is non-uniform, the relation of the blast wave's overpressure with the angle is approximately cosine function, and the variation amplitude increases along with the increase of charge velocity.Also, we analyzed the correlation between the static and the dynamic blasting shockwave field, and established the engineering calculation model for the dynamic blasting shock wave overpressure.The modeling results agree well with the dynamic experimental and simulation results.

As a novel technique, the magnetically driven ramp wave compression has attracted considerable attention of specialists in hydrodynamics.In this paper, we analyzed the loading process of magnetically driven ramp wave compression.Then we derived the experimental uncertainty transfer equations based on the forward Lagrangian analysis method, and estimated the uncertainties of the experimental results obtained by the backward integration method.There was good agreement between the two different methods.The results show that the relative uncertainties of the sound speed and the stress obtained in the magnetically driven ramp wave compression experiment are less than 1.5% and 2.5%, respectively.It shows that the magnetically driven ramp wave compression technique is a high-precision and reliable loading technique.

To reveal the suppression chemical mechanism of nitrogen and water and to prevent the methane-air explosion more effectively, we designed different schemes with different concentrations of nitrogen and water vapor, and simulated the pressure, temperature and time to peak pressure of the methane-air explosion using a chemical kinetic software.We compared the reaction rates of main elementary reactions of different schemes, and analyzed the suppression chemical kinetics mechanism.The results show that both the nitrogen and the water vapor can effectively suppress the elementary reaction rate of the explosion, and the water vapor is more efficient than the nitrogen.Meanwhile, the concentration of free radical OH· will increase with water vapor as the inert gas.This research results can provide reference for the study of the explosion suppression of methane-air mixture.

A reactive material with the density of 5.2 g/cm³ was impacted by high velocity flyers launched by a ∅57 mm powder gun and, for the first time in research, its particle velocities and shock wave histories were measured with embedded electromagnetic particle velocity gauges.The results indicated that, though the reactive material could be initiated when impacted by high velocity flyers, its reaction rate was slow and its energy release process lasted for a long time, the reaction is not self-sustained.By comparing the particle velocities of the reactive material with those of PBX 9502 and the inert material, we found that the reaction characteristics of the reactive material can be defined as somewhere between those of PBX 9502 and the inert material.This method can be applied to researches on the reaction characteristics of other reactive materials, and the corresponding experimental results provide reference to the materials choice and reactive fragments design for reactive fragment warheads.

Numerical simulation and experimental methods were utilized to study the influence of material type on the morphology of the flyer in the field of MEMS booster train based on micro charge involving copper azides.The research results indicate that titanium is suitable for flyer material, while copper, aluminum and polyimide are not.The flyer morphology is closely related to the mechanical properties of material.The integrity of the metal flyer depends mainly on the effective plastic failure strain, while that of the non-metal flyer depends mainly on the Young's modulus.

Based on the analysis of the ignition characteristics of the fragile penetrator, the ignition experiments for No.0 diesel fuel were carried out to investigate the influence of the incident velocity, the incident angle, and the cross-section shape of the projectile and the thickness of the target on the ignition characteristics of the fragile tungsten alloy projectile.The results show that the ignition characteristic is improved with the increase of the incident velocity; to a certain degree, the ignition characteristic is improved with the increase of the target thickness, and then weakened with the further increase of the target thickness; the fragile projectile with a triangular cross-section has a better ignition characteristic than that with a circular cross-section at different incident velocities and incident angles.

In this work high flash-point jet fuel containing different proportions of explosion-suppressive material, called as explosion-suppressive high flash-point jet fuel, was prepared.The liquid fuel combustion and explosion performance evaluation devices were used to measure the explosion parameters of the fuel under different conditions of the spray pressures in the range of 0.343, 0.687, 1.030, 1.373 and 1.717 MPa.The results from the experiment show that the explosion will be more sufficient with the increase of the spray pressure, and the explosion-suppressive capability of the high flash-point jet fuel becomes stronger as the content of the explosion-suppressive material proportion increases.Further, to study the internal relationship between the atomization property and the explosion-suppressive characteristics, the droplet size distribution under the spray pressure of 1.717 MPa was measured using the Malvern particle size analyzer.Based on the above research results, the explosion-suppressive mechanism of the explosion-suppressive high flash-point jet fuel was discussed in detail.

In this paper, we developed a visible light intensified charge coupled device (ICCD) and introduced its key elements including the coupler, the fast pulse power and the high-precision delay synchronization control unit.The test results show that the ICCD's shortest exposure time is 5 ns, and the image spatial resolution is better than 37 lp/mm.Using this newly developed ICCD, we set up a special transmission schlieren optical system for measuring the process of high-voltage air discharge, and obtained remarkably clear images, thereby enabling the ICCD to present a high-quality level and meet such ultrafast transient diagnostic requirements as plasma discharge, ejecta analysis, bioluminescence, laser induced fluorescence, and possess a broad application prospect.

In the present work we simulated the process of a sub-caliber projectile moving in the bore of a DAVIS gun using the finite element method based on the LS-DYNA calculation program.By loading the pressure of the gases from the propellant burning on the pushing module, we calculated the stress of the test accessories moving in the bore and checked its strength.Further, we verified the safety of the test accessories of the sub-caliber projectile using the simulation and the experimental results.This analysis can serve as a reference for refining the sub-caliber launching technique of the DAVIS gun and other guns.

In this work we studied the effect of extreme high hydrostatic pressure treatments (700-1 200 MPa) on the texture and cytoderm microstructure of carrot slices compared with heat treated and untreated samples, and examined the changes of their texture and cytoderm structure during the storage days (7 d).The results show that the carrot slices treated by 700, 800, 900, 1000, 1 100 and 1 200 MPa high pressures presented a decrease of 67.65%, 72.17%, 67.30%, 74.05%, 77.67%, 62.46% in hardness, respectively.However, there was no significant correlation (P > 0.05) between the changes of hardness and pressure.With the extension of processing time, the hardness of carrot slices decreased correspondingly, when the treatment pressure was below 1 000 MPa.The adhesiveness and resilience of the samples decreased significantly (P < 0.05) after the pressure treatment and the cytoderm ruptured.The hardness of samples decreased gradually with the extension of storage time.The pectin in the cytoderm degraded, coupled with the collapse of the cytoderm and the disappearance of the rigid cell structure.