It is an effective way to initiate detonation with the aid of a pre-detonator in the detonation engines, and the initiation process by the pre-detonator has been widely investigated in static and subsonic flows. However, how to initiate a detonation wave with a pre-detonator in the supersonic flow was little dealt with in the literature and still needs to be intensively investigated. The diffraction and re-initiation processes during a planar detonation wave propagates into the supersonic inflow were numerically investigated in this paper. The detonation initiation processes both in a semi-infinite space and a confined channel were studied. The governing equations are two-dimensional in-viscid Euler equations. The high-accuracy WENO scheme was utilized in the simulations. The chemical reaction model is a two-step chain branching kinetic model with induction and reaction steps. The cellular structure of detonation wave is regular which is corresponding to the detonation wave formed in the detonable mixture highly diluted with inert gas. It was shown that the maximum distance of detonation propagation increased as the Mach number of supersonic inflow in the semi-infinite space. More transverse waves were generated outside the kernel zone. However, the re-initiation of detonation was failed in the geometry utilized in this work. In the confined channel, the re-initiation process was greatly influenced by the reflected waves. The emerged flow was compressed at the upstream side when the supersonic inflow was added and the pressure of the shock wave was increased accordingly. Compared with the failure of detonation re-initiation in the static flow, the re-initiation of detonation was successfully triggered in the supersonic inflow with Ma=2.0, despite the two cases used the same geometry. It was because that the wrinkles occurred on the reaction front and then resulted in the generation of transverse waves in the supersonic inflow. Because of the collisions between transverse waves, or between the transverse wave and the wall, the pressure decay of the leading shock wave was suppressed. Consequently, a successful re-initiation of detonation was occurred.

In order to study reaction properties of Al-teflon with different particle sizes, we prepared Al-teflon reactive material powders by mixing Al powder with particle sizes of 25 μm, 1 μm, and 20-200 nm, where micron-sized teflon powder as raw materials. The laser ablation experiments of Al-teflon reactive material were performed by a pulsed laser system. The self-luminescence imaging and emission spectra in the reaction process were collected and analyzed by ICCD camera and spectrometer. The results show that the reaction properties of Al-teflon reactive material under laser ablation reflect the characteristics of typical secondary reactions, together with continuous combustion characteristics and obvious afterburning effects, and the total energy release time is long. At the same time, the reaction properties is closely related to the particle size of Al powder. As the particle size of Al powder decreases, the reaction becomes more violently in the initial reaction stage. As the reaction progresses, the subsequent reaction capability of the corresponding reactive material with nano-Al size powder gradually decreases, the reaction intensity and reaction time are not as good as the corresponding reaction materials of 1 μm size aluminum powder.

Accidental initiations of the explosive subjected to mechanical or thermal loads have caused numerous catastrophic tragedies. The impact sensitivity and thermal safety of explosive is of great importance for the applications. Previous work showed an evident decline on modulus with increasing cook-off temperature, which suggest that Cook-off temperature may affect the deformation process of the impacted PBX, and further affect the critical impact velocities for initiation. In this work, to investigate the mechanical and thermal response of confined PBX charge under low velocity impact of a small projectile during cook-off events, a finite-element model was established to provide reliable prediction of explosive safety performance at high temperature. A thermal-mechanical-combined experiments from literature enabled comparisons between simulated results and measured data for the critical impact velocities of initiation for a HMX-based PBX charge (HMX/TATB/olefin). The simulation results showed that when it was heated up to 348.15 K, the critical impact velocity of initiation for the explosives reached the maximum (360 m/s). With the increase of cook-off temperature, the localized heating regions change from the surface of explosive charge to the center. This phenomenon was caused by the effect of compression overshadows shearing on the initiation because of the strength decreases in the heated PBX, implying that thermal softening plays an important role in the impact sensitivity of the heated PBX charge.

In order to obtain the chemical reaction zone of HMX based JOB-9003 explosive, experimental measurements on the detonation wave profile of solid explosives using photon Doppler velocimetry (PDV) have been performed. Planar detonations were produced by impacting the explosive with sapphire flyer launched from a powder gun. Particle velocity wave profiles were measured at the explosive/window interface. LiF windows with very thin vapor deposited aluminum mirrors were used in the experiments. The time resolution of PDV is about 1 ns, and the velocity uncertainty  is less than 2%. The measurements show distinct end to the reaction zone indicating a CJ point in JOB-9003. The results show that the reaction time of JOB-9003 is (11±2) ns, and the corresponding reaction length is (0.075±0.014) mm. The CJ pressure is (35.6±0.9) GPa, and the pressure at Von-Neumann spike is (47.9±1.2) GPa.

To find out about the patterns and regularities of the reaction growth of shock initiation on JB-9014 explosives, using aluminum-based multiple EMV, we conducted six one-dimensional planar impact experiments in the gun-power platform. Under different initial pressures (11.33−14.18 GPa), we measured the particle velocity versus time u_p(t) and wave-profiles in the JB-9014 explosive at 9 different distances from the impact plane, and recorded the position of the shock front with time x(t), successfully fitting the unreacted explosive JB-9014 Hugoniot relation. Furthermore, we obtained the time and distance to detonation are estimated according to both the wave-profiles and the x(t) trajectories from the shock wave tracker gauges.

Based on the wave propagation characteristics of variable cross-section rods, a generalized wave impedance gradient flyer, termed the " bed of nails” was designed. The process of the generalized wave impedance gradient flyer impacting the sample was simulated by using the SPH algorithm of the LS-DYNA software. The wave profiles display a smooth increase of  velocity, with no indication of a shock jump. The physical mechanism of the quasi-isentropic compression generation is attributed to the interaction from a series of approximately spherical waves with slowly rising front. The influences of impact velocity and geometric parameters of the flyer on the ramp wave loading characteristics were discussed in detail, which provide some useful information  for the design and application of the generalized wave impedance gradient flyer. Selective Laser Melting, and an additive manufacture technique, were used to manufacture  the " bed of nails” flyer. The experiments were performed at the impact velocities of 348 m/s using the 57 mm gas gun. The measured free surface velocity profile agrees well with the simulation results.

Based on the Navier-Stokes equations, the large-eddy simulation code MVFT (multi-viscous-flow and turbulence) was applied to numerically study the Richtmyer-Meshkov instability (i.e. RMI) for a perturbed interface, which is driven by a non-planar shock wave with Ma=1.25 in uniform and non-uniform flows with Gaussian distribution of the initial density. The simulation results show that the interface evolution of the RMI induced by non-planar shock wave is affected by the non-uniformity of the initial flows. Before reshock, the growth of the disturbed interface increases with the increasing of the non-uniformity flow field for either φ=0 or φ=π. However, these discrepancies are reduced as the flow enters the turbulent mixing. Further quantitative analysis of the circulations and high-order fluctuating velocity correlation in the flow field reveal the mechanisms for the aforementioned regulations. In addition, it is found that the interface evolution of the RMI induced by non-planar shock wave is different from that driven by planar shock wave. The mechanism for the difference is the influence of the initial vorticity of non-planar shock wave and the vorticity generated by the shock-interface.

The mathematical-physical model used to describe the detonation  dynamics has many  uncertain factors due to the complexity and lack of knowledge for detonation phenomenon. Quantifying and assessing the impact of input uncertainties on output of detonation systems has a direct influence on reducing the risk based on the numerical model  and simulation results for detonation. The Wiener chaos based on adapted basis is used to deal with the uncertainty quantification of high-dimensional random variables for detonation simulation. The rotation transformation and projection method is used  to reduce the length of truncation number.  Rosenblatt transformation is used to transform the set of dependent random variables into independent random variables. The equality of probability principle is used to change the non-Gaussian random variables into standard random variables. Uncertainty quantifications of the cylinder test with high dimensional input uncertainties are studied. The statistical informations such as mean, standard deviations, and confidence intervals are presented. The simulation  results coincide with the experimental data, and the accuracy of the model is validated.

In this work, to obtain the pressure state of underwater explosion in near-field, we numerically simulated the whole process of underwater explosion using the smoothed particle hydrodynamics and adopting the C-J detonation model, and following the empirical formulas, confirmed the laws of the peak pressure, thereby verifying the effectiveness of the numerical program. We also analyzed the waves' propagation in underwater explosion and compared it with the numerical results of underwater explosion in various dimensions. The results show that the distance ratio R/a=6 is a demarcation point in the waves structure, and in the R/a＜6 near-field range the fitted peak pressure curve should be divided into two sections. Further, we performed segmented fitting of the numerical results with power function, and found the fitted curve in good agreement with the numerical results.