Study on the influence of side-blown airflow velocities on plasma and combustion wave generated from fused silica induced by combined pulse laser

This study examines the impact of variations in side-blowing airflow velocity on plasma generation,combustion wave propagation mechanisms,and surface damage in fused silica induced by a combined millisecond-nanosecond pulsed laser.The airflow rate and pulse delay are the main experimental variables.The evolution of plasma motion was recorded using ultrafast time-resolved optical shadowing.The experimental results demonstrate that the expansion velocities of the plasma and combustion wave are influenced differently by the sideblowing airflow at different airflow rates(0.2 Ma,0.4 Ma,and 0.6 Ma).As the flow rate of the sideblow air stream increases,the initial expansion velocities of the plasma and combustion wave gradually decrease,and the side-blow air stream increasingly suppresses the plasma.It is important to note that the target vapor is always formed and ionized into plasma during the combined pulse laser action.Therefore,the side-blown airflow alone cannot completely clear the plasma.Depending on the delay conditions,the pressure of the side-blowing airflow,the influence of inverse Bremsstrahlung radiation absorption and target surface absorption mechanisms can lead to a phenomenon known as the double combustion waves when using a nanosecond pulse laser.Both simulation and experimental results are consistent,indicating the potential for further exploration of fused silica targets in the laser field.

The Process of a Laser-Supported Combustion Wave Induced by Millisecond Pulsed Laser on Aluminum Alloy

We study the process of a laser-supported combustion wave （LSCW） when an aluminum alloy is irradiated by a millisecond pulse laser based on the method of laser shadowgraphy. Under the condition of different laser parameters, the obtained results include the velocity, ignition threshold of LSCW and the variation law. The speed of LSCW increases with the laser energy under the same irradiation laser pulse width, and the speed of LSCW reduces with the increase of the laser pulse width under the same irradiation laser energy. Moreover, the ignition time of LSCW becomes shorter by increasing the laser number of the pulse and is not effected by changing the frequencies, when keeping the laser pulse width and energy unchanged. The results of the study can be applied in the laser propulsion technology and metal surface laser heat treatment, etc.

Nonlinear Dynamic Characteristics of Combustion Wave in SHS Process

The characteristic of combustion wave and its change were analyzed by numerical value calculation and computer simulation, based on the combustion dynamical model of SHS process. It is shown that with the change of condition parameters in SHS process various time-space order combustion waves appear. It is concluded from non-liner dynamical mechanism analysis that the strong coupling of two non-linear dynamical processes is the dynamical mechanism causing the time-space order dissipation structures.

Combustion Characteristics of Solid Sustained-Release Energetic Materials

A solid sustained-release energetic material sample,an eruption device and a complete test system were prepared further to analyse the combustion characteristics of solid sustainedrelease energetic materials.The high-temperature heat flux generated by the combustion of the samples from the eruption device was used to penetrate the Q235 target plate.In addition,the meaning and calculation formula of energy density characterising the all-around performance of heat flux were proposed.The numerical simulation of the combustion effect of samples was carried out.According to the data comparison,the numerical simulation results agreed with the experimental results,and the maximum deviation between the two was less than 8.9%.In addition,the structure of the combustion wave and high-temperature jet was proposed and analysed.Based on theoretical analysis,experimental research and numerical simulation,the theoretical burning rate formula of the sample was established.The maximum error between the theoretically calculated mass burning rate and the experimental results was less than 9.8%.Therefore,using the gas-phase steady-state combustion model to study the combustion characteristics of solid sustained-release energetic materials was reasonable.The theoretical burning rate formula also had high accuracy.Therefore,the model could provide scientific and academic guidance for the theoretical research,system design and practical application of solid sustained-release energetic materials in related fields.

Study on the effect of focal position change on the expansion velocity and propagation mechanism of plasma generated by millisecond pulsed laser-induced fused silica

In this work, by controlling the positional relationship between the target and the focal point, the surface damage, shock wave phenomenon and propagation mechanism involved in the plasma generation of fused silica by millisecond pulsed laser irradiation at different focal positions were studied. Laser energy is an important experimental variable. The dynamic process of plasma was detected by optical shadow method, and the influence of surface film damage on plasma propagation and the propagation mechanism at different focal positions were discussed. The study found that the plasma induced by the pulsed laser at the focus position within 0–20 μs exploded, the micro-droplets formed around 20 μs. At the same time, a shock wave is formed by the compressed air, the micro-droplets are compressed under the action of the shock wave recoil pressure, and the micro-droplets channel phenomenon is observed in the micro-droplets. The peak velocities of plasma and combustion wave appear earlier in the pre-focus position than in the post-focus position. This research provides a reference for the field of laser processing using fused silica as the substrate.

Experiment Study on Shock Induced Reaction Process of Ti+Si Reactive Powder

A phenomenon of shock wave reacceleration was studied when Ti＋Si reactive powder is loaded by a high-speed flyer.The self-propagating reaction in the Ti＋Si reactive powder was triggered by the high speed impaction of the flyer launched by a two-stage gas gun.In the process of self-propagating reaction,a strand of optical fiber and the electric pins were used to measure the velocity of shock wave propagation.The experimental results showed that the initial velocity of shock wave in the reactive powder was a few hundred meters per second,and then it decreased obviously with the increase of propagation distance.This phenomenon was also verified in the process of a pure Si powder loaded by a shock,while the phenomenon of shock wave reacceleration was not observed in the Ti＋Si reactive powder.