Papers by Keyword: Ablation

Abstract: This study focused on the mechanical properties and ablation properties of liner insulation in rocket motors for improving rocket performance by means of tensile strength, elongation, ablation rate and density. The following parameters were varied: amount of zinc oxide, antimony trioxide and carbon black (N550). It was found that the insulation of the rocket motors with antimony trioxide and carbon black provided higher the elongation and ablation rate. Thus, it was able to endure more heat from hot gas in combustion chamber. The result suggests that use of antimony trioxide and carbon black as filler in liner insulation can improve the thermal insulators and case-bonded in rocket motor between the solid propellant and the rocket motor tube.

Abstract: The present research reports the influences of variant phenolic resin concentrations on the thermo-mechanical and ablation characteristics of ethylene propylene diene monomer (EPDM) elastomer. Backface temperature acclivity (BTA), charring rates, and insulation indexes were executed for the fabricated composite specimens. It was noticed that BTA was enhanced while linear/radial/mass ablation rates were significantly diminished with increasing concentration of phenolic resin (PR) in base matrix (elastomeric polymer). The composite (30wt%PR/EPDM) has 25% high thermal endurance compared to virgin EPDM composite. Thermal conductivity was increased with increasing PR to EPDM ratio. PR incorporation has remarkably enhanced the ultimate tensile strength of the EPDM elastomer. An efficient improvement in elastomeric hardness was also observed with increasing PR contents in EPDM matrix. Scanning Electron Microscopy (SEM) results showed the porosity generation and polymer melting during ablation.

Abstract: Modern approaches to the creation of single-layer and multi-layer high-temperature coatings for the protection of heat-resistant carbon-containing composite materials from oxidation and erosion in the high-speed fluxes of oxygen-containing gases are analyzed. Particularly have been outlined the heat-resistant coatings, the main components of which are either super refractory transition metal borides (ZrB₂, HfB₂, TiB₂) with the addition of carbides (SiC, ZrC, HfC, TiC, TaC), silicides (MoSi₂, TiSi₂, ZrSi₂, TaSi₂, WSi₂) and nitrides (HfN, ZrN, TiN), or refractory oxides (HfO₂, ZrO₂), or more complex synthetic compositions based on oxide ceramics. The results of fire gas-dynamic tests of coatings of perspective compositions are presented. The potential architecture of ultra-high-temperature coatings with high efficiency of protective action is justified.

Abstract: In this work, TiB₂-MoSi₂ composite coatings with various contents of MoSi₂ (20 vol. % and 40 vol. %, respectively) were fabricated on SiC coated C/C substrates by low pressure plasma spray (LPPS) technique. The microstructure and phase composition of the coatings were characterized. The ablation behaviors of the composite coatings were evaluated and compared with the pure TiB₂ coating using a plasma flame of about 2200°C. The results showed that MoSi₂ was uniformly distributed in the TiB₂ matrix. All the coatings kept intact after the ablation for 60s - 180s, indicating their excellent ablation resistance. The addition of MoSi₂ had great influence on the ablation behavior of the composite coatings. The TiB₂ coating gained mass after the ablation. The mass of the TM20 coating increased firstly (60s and 120s) and then decreased at 180 s. Mass loss was observed for the TM40 coating during the whole procedure of ablation test.

Abstract: Thermal damage of workpiece material induced by laser machining process can be reduced by using the underwater technique. This method requies the whole workpiece to be submerged in water while a laser beam strikes the work surface for ablation. Though water can cool the workpiece during the ablation, the dynamic features of water can adversely interfere the laser beam. The vapor bubbles created in water can scatter the laser beam and in turn attenuate the laser intensity at the work surface so as the ablation performance. In this paper, the bubble formation caused by laser machining of silicon in water was investigated and analyzed. The shadowgraph technique associated with the high speed camera was used to capture and measure the vapor bubble in water. The bubble size was found to increase with the laser pulse energy. After a number of laser pulses irradiated on the workpiece surface, the bubble was broken up into small ones which can significantly disturb the laser beam so as the ablation performance.

Abstract: The result of direct ablation of silicon by an 800 nm Ti:Sa femtosecond laser pulses are presented. Obtained slice of silicon with submicron roughness with tilt focused femtosecond laser pulses. Yaw cut more due to mechanical vibrations of the entire installation on a pneumatic table, but not the physics of the ongoing process. During processing, possibly thinning the silicon sample from the opposite edge (sharpening) to submicron values ​​(tens of nanometers).

Abstract: Thermal protection materials are required to preserve the metal components of motor that suffer severe heat load. The research on thermal response of insulation of ramjet combustion chamber was carried out by the ground test and numerical simulation. During the working time of the ramjet, the back-face temperature of the thermal protection material was measured. The scanning electron microscope of samples was investigated. The calculation of thermo-chemical flow was solved by the CFD software FLUENT to provide the heat load boundary for simulation of heat transfer of EPDM insulation. The heat transfer model was solved by the FEA software ANSYS. Comparison of the temperature profile at the ablating surface between calculation and measurement shows the two results agree with each other. The simulation results can provide the temperature rising trend of insulation in a certain extent.

Abstract: The system model «high power ion beam – metal» is suggested. Regularities of impulse formation of mechanical load in the volume of metal target subjected to the action of ion beams of different component composition in the range of power density 10⁷...10¹⁰ W/cm² have been considered. The influence of generation mechanisms on the profile and amplitude-to-time parameters of shock-wave excitation is studied.

Abstract: In the Paper, an analysis of laser modification of the surface of specimens produced of powder steel 1.2083 by SLS (selective laser sintering) method is carried out. Three main structures being formed on laser modification of the sintered steels are presented: periodical, interim and degrading. The dependence of the changes of the technological parameters of the laser equipment on the geometrical parameters of the specimen under processing is provided.

Abstract: For oblique incidence of laser radiation on the target, the breakdown of air and erosive jet are separated in time and space. The electron density is higher in the air breakdown area while Al I density is higher in an erosive plume area. We also defined plasma expansion mechanism and estimate the time of erosive plume formation.