Thermal Erosion Behaviour Research Articles

An interface shear damage model of chromium coating/steel substrate under thermal erosion load

The Cr-plated coating inside a gun barrel can effectively improve the barrel’s erosion resistance and thus increase the service life. However, due to the cyclic thermal load caused by high-temperature gunpowder, micro-element damage tends to occur within the Cr coating/steel substrate interface, leading to a gradual deterioration in macro-mechanical properties for the material in the related region. In order to mimic this cyclic thermal load and, thereby, study the thermal erosion behavior of the Cr coating on the barrel’s inner wall, a laser emitter is utilized in the current study. With the help of in-situ tensile test and finite element simulation results, a shear stress distribution law of the Cr coating/steel substrate and a change law of the interface ultimate shear strength are identified. Studies have shown that the Cr coating/steel substrate interface’s ultimate shear strength has a significant weakening effect due to increasing temperature. In this study, the interfacial ultimate shear strength decreases from 2.57 GPa (no erosion) to 1.02 GPa (laser power is 160 W). The data from this experiment is employed to establish a Cr coating/steel substrate interface shear damage model. And this model is used to predict the flaking process of Cr coating by finite element method. The simulation results show that the increase of coating crack spacing and coating thickness will increase the service life of gun barrel.

Numerical study of thermal erosion behavior of RPV lower head wall impinged by molten corium jet with particle method

Erosion behavior of RPV lower head wall is of significance in the late in-vessel stage of a nuclear reactor severe accident. In the present study, a numerical modeling based on MPS method was completed and validated against the experimental data, and then the thermal erosion mechanisms of lower head wall by different molten corium jets were analyzed and the approach of coating a ZrO2 liner to delay the thermal erosion was proposed. The results indicated that the heat transfer to lower head wall was dominated by forced convection for molten SS jet condition, while for Zr, ZrO2 and UO2 jet conditions the heat transfer at lower head wall surface was mainly through conduction due to the existence of crust and melted carbon steel layer. The insulating effect of the crust and melted carbon steel layer could delay the thermal erosion significantly, but the impingement of molten SS jet with superheat degree at about 300K or higher was a great threat to lower head wall integrity. The sensitivity analysis of the effect of ZrO2 liner on lower head wall thermal erosion demonstrated that it could effectively delay the erosion by molten metal jets.

Two-phase mass injection from the stagnation zone of a blunt body in a hypersonic flow

A mathematical model of the hypersonic steady gas flow over the stagnation zone of an axisymmetric blunt body ~Mth given twophase injection from the surface is proposed. The two-continuum model of a dusty gas [3] is used for describing the flow in the region of the walt. The problem is solved in the boundary layer and thin viscous shock layer approximations. On the basis of the numerical calculations the distribution of the parameters of the carrier and dispersed phases near the axis of symmetry is obtained. The similarity parameters determining the convective heat transfer are found. The stagnation point heat fluxes w~th and without particles are compared. The range of parameters on which particles can significantly reduce the heat transfer is determined. Research into the thermal erosion behavior of various materials in high-enthalpy gas flows and, moreover, the development of new active thermal protection techniques [1--3] make it necessary to investigate the effect on the thermal load of dispersed particles introduced into the flow from the body surface. In the above-mentioned applications a mixture of gas and disperse particles, which then move in a narrow region near the wall, is injected from the surface. Two-phase injection into a supersonic flow without allowance for the viscosity and thermal conductivity of the carder phase was previously considered in [4]. The influence of particles on the flow in the boundary layer without injection effects was investigated in [5, 6].

Thermal erosion behaviour of carbon and boron-carbon materials during simulated plasma disruptions

Results from disruption simulation experiments are described in which specimens were exposed to 3.8 MJ m −2 energy deposition during about 10 ms from a hydrogen plasma with a density of 3×10 20 m −3 and a temperature of about 10 eV. The materials tested were pure graphite, graphite with 3 to 30% boron addition, B 4 C coat mix material, and plasma sprayed B 4 C coatings on graphite. The interaction of the thermally eroded material was measured by emission spectroscopy. The results show that the addition of boron to graphite does not significantly change the thermal erosion behaviour, or the formation of a vapour cloud in front of the specimen surface. B 4 C coat mix material melted and the eroded species show a much weaker interaction with the incident plasma than the graphite materials.

Thermal erosion behaviour of carbon and boron-carbon materials during simulated plasma disruptions

Thermal erosion behaviour of carbon and boron-carbon materials during simulated plasma disruptions

Simulation and Analysis of the Response of Carbon-Fiber Composites and Pyrolytic Graphites to Off-Normal High Heat Loads

The response of plasma-facing materials to off-normal high heat loads expected in Next European Torus/International Thermonuclear Experimental Reactor (NET/ITER) disruptions has been studied by both experimental and numerical simulations. Experiments have been performed on a number of pyrolytic graphites and carbon-fiber composites. The measured erosion is compared with numerical predictions by a transient heat load code. The effect of variations in thermophysical material parameters on thermal erosion behavior is discussed. Cracking is observed on the surface of pyrolytic graphites, even below the erosion threshold.

Simulation and analysis of the response of carbon materials to off-normal heat loads accompanying plasma disruptions

The effects of off-normal heat loads accompanying plasmadisruptions have been studied by both experimental and numerical simulations. Experiments have been performed on a range of polygranular graphites, pyrolytic graphite and carbon composite material. The measured erosion is compared with numerical predictions by a transient heat load code taking a revised value for the vaporization enthalpy of carbon. The effect of variations in thermo-physical material parameters on thermal erosion behaviour is discussed.

Thermal erosion of graphite by pulsed electron beam

Electron beam heating tests were performed for several kinds of Isotropie graphite to evaluate the dependence of thermal erosion behavior on the graphite species and on the heat load. The specimens were irradiated by electron beams with power densities of 25 to 45 MW/m 2 and a pulse length of 2.0 s. A crater caused by erosion was found to be the major damage and preferential erosion was observed at the grain boundaries. In some kinds of graphite, a large weight loss caused by thermal erosion, which exceeded the expected weight loss due to sublimation, was observed. In these cases, some of the ejected bulk graphite particles that had collected on a Mo sheet were observed with an optical microscope. These results suggest that some kinds of graphite will be eroded mainly by the “particle emission” mechanism under high heat loads.