Papers by Keyword: Spallation

Abstract: Material choices for liquid lead bismuth spallation target are some of austenitic stainless steel, ferrite martensitic steel and cold-worked austenitic stainless steel. In order to ensure materials resistance to irradiation and corrosion as well as compatibility with lead bismuth, it is appropriate to lower the incident proton current density and the process temperature, in which temperature range engineering design can control to work, especially in ADS (Accelerator-Driven nuclear transmutation System) concept. The lower limit temperature is determined from the physical melting temperature and the engineering efficiency of the steam generator involved in process control. The material related issues for liquid lead bismuth are mass loss by impinging secondary flow, wettability at the device interface for ultrasonic waves application, detachable control of the slag in the flowing system, stabilized electrical resistance between the material and the liquid lead bismuth interface. Electromagnetic fluid analyses show how flow rate relates electrical resistivity of flow channel material.

Abstract: This research investigates the effect of heat treatment on the isothermal oxidation behaviour of Fe-33Ni-19Cr alloy. The samples were undergone heat treatment at three different temperatures namely, 1000oC, 1100oC and 1200oC for 120 minutes of soaking time followed by water quench to differ the grain size of alloy. The heat-treated sample was ground by using SiC paper atP600 finished. The samples were weighed using analytical balance and the surface area was measured before oxidation test. The heat-treated Fe-33Ni-19Cr alloys were isothermally oxidized at 850oC for 150 hours. The characterization on oxidized samples were carried out using scanning electron microscope equipped with energy dispersive x-ray (SEM-EDX) and x-ray diffraction (XRD). The result shows that, the average grain size increases as the heat treatment temperature increased. Fine grain size develops higher grain boundary area which acts as an ion diffusion path across the metal-gas interface during oxide formation. HT1000 sample with fine grain structure shows minimum weight gain and low oxidation rate compared to HT1100 and HT1200 samples. Uniform oxide layerformed on surface of the fine grain size sample. Whereas spallation of oxide scales was identified on the coarse grain size sample. Phase analysis shows that the oxidized sample formed several oxide phase.

Abstract: An investigation of spallation behaviors of plasma-sprayed ZrO₂-7wt.%Y₂O₃ (7YSZ) splat at high temperature was carried out to understand the failure mechanism of thermal barrier coating (TBC). In present work, 7YSZ splats prepared by atmospheric plasma spray (APS) were collected on mirror polished NiCoCrAlYTa bond coating holding at 250 °C, where the nickel base superalloy K4169 was used as substrate. Then the samples with splats were taken into air furnace for isothermal oxidation test at 900 °C for different time. The surface of splat and cross section of splat-bond coating interface during isothermal test were characterized using a focused ion beam (FIB) assisted field emission scanning electron microscope (FE-SEM). Besides, the compositions of thermally grown oxide (TGO) layer at splat-bond coating interface were analyzed after oxidation test. In addition, the schematic diagram of spallation process and oxidation model of splat has been presented at relatively high temperature.

Abstract: The present paper analyzes the phenomenon on spallation and failure of driven pile. Based on the nonlinear program LS-DYNA, the dynamical performance of driven pile into the soft soil foundation is studied by numerical simulation. Taking into account the stress-wave theory, some analyses are conducted to discuss the influence factors on spallation and failure of driven pile. The analysis results show that the compression and tension of stress wave plays an important role in the process of pile driven. Some guidance and reference is useful for the design, manufacturing and construction of piles.

Abstract: In the present study the oxidation behaviour of a number of candidate alloys for heat exchanging components was investigated in model gas mixtures containing high amounts of CO₂ and/or water vapour in the temperature range 550-700°C up to exposure times of 1000 h. During exposure in Ar/CO₂ and Ar/CO₂/H₂O base gas mixtures at 550-650°C the oxidation rates and scale compositions of martensitic 9-12%Cr steels were similar to those previously observed in steam environments. Thin and protective Cr-rich oxide scales which are commonly found during air oxidation was observed locally on the specimens surfaces after oxidation in Ar-(1-3%)O₂-CO₂. The tendency for protective chromia base scale formation increased when 3% oxygen was added, especially for the 12%Cr steel. When iron base oxide scales were formed on the metal surface, the martensitic steels tended to exhibit carburisation whereby the extent was reduced by increasing the water vapour and oxygen contents. All three studied austenitic alloys exhibited very slow scale growth rates at 550°C, however, at and above 600°C the steels with lower Cr content started to form two-layered iron rich surface oxide scales whereby the outer oxide was prone to spallation upon thermal cycling. The high-Cr austenitic steel 310N and the nickel base alloy 617 formed very thin, Cr-rich oxide scales at all used test temperatures and atmospheres. For those two materials the oxidation behaviour in gases containing water vapour in combination with intentionally added oxygen was affected by formation of volatile chromium oxyhydroxide.

Abstract: Based on the 3D plane impact and 2D MCA numerical simulation, the 3D ANSYS/LS-DYNA software is applied to conduct numerical simulations on two kinds of impact breaking process of a glass ball, during which spallation phenomenon occur. The Von Misses stress of each node changes with the time as the result of the stress waves spreading, reflecting and overlapping within the material. The stereograms and profiles from the simulation results reveal that the stress of each node changes with the time. By comparing the simulation results of plane impact and 2D point impact, differences and similarities between these processes are illustrated in this paper, which reflects the complexity of mechanics in the processes.

Abstract: Ti(Al,O)/Al2O3 and TiAl(O)/Al2O3 composite coatings have a potential to reduce dissolution and aluminium soldering tendency of H13 tool steel used in the aluminium processing industry. The thermal shock resistance of H13 tool steel coated with Ti(Al,O)/Al2O3 and TiAl(O)/Al2O3 composite powders sprayed using a high velocity oxygen fuel (HVOF) technique was studied. The thermal shock behaviour of the composite coatings was investigated by subjecting the coated coupons to a number of cycles, each cycle consisting of a holding time of 30 seconds in molten aluminium at 700 ± 10 °C followed by quenching into water. The surfaces of the coupons were examined for Al soldering and an evaluation of surface spallation. Any cracks found in the coatings were studied to explain their thermal shock behaviour. The results of this study showed that both Ti(Al,O)/Al2O3 and TiAl(O)/Al2O3 composite coatings on H13 tool steel have good thermal shock resistance with a thermal shock life between 300 to 400 cycles. The composite coatings and fracture surfaces were analyzed using scanning electron microscopy.

Abstract: Damage prediction, adhesion strength and remaining lifetime of TBC are highly important data for understanding and preventing TBC spallation on blades. LAser Shock Adhesion Test (LASAT) is a powerful method to measure adhesion of coating due to its rapidity, simplicity and capabilities to distinguish different strength levels and the easy damage observation in case of TBCs. A new protocol of LASAT has been introduced in order to measure the adhesion level of the ceramic coating from the exploitation of the two-dimensional effects that promotes a shock wave pressure-dependent size of the damage. Finite element modeling, taking into account the TBCs dimensions, showed the edges effect on interfacial stress applied by laser shock.

Abstract: Spallation of concrete under dynamic loading has been the hot issue of concern about civil engineering structures and protective engineering. In the present paper, the principle of propagation of stress wave and the induced spallation process along a one-dimensional bar and the RFPA-Dynamics code which considers the heterogeneity of the concrete materials are briefly introduced. In order to numerically investigate the effect of mesh size of numerical model on the computational results, the failure process of concrete with three mesh sizes under dynamic loads was numerically simulated using RFPA-Dynamics code. Numerical simulations show that the failure patterns of concrete with different mesh sizes under dynamic stress waves are different. It is found that for the numerical models with the same mechanical parameters, the smaller mesh size of the numerical model is, the longer propagation of stress wave delay, the smaller the compressive stress is, thus the greater the tensile stress is, and the number of cracks is increasing, in general, rupture is more serious. The accuracy of mesh is little to improve when the number of the grid increases to a certain value.

Abstract: Orientation-imaging microscopy offers unique capabilities to quantify the defects and damage evolution occurring in metals following dynamic and shock loading. Examples of the quantification of the types of deformation twins activated, volume fraction of twinning, and damage evolution as a function of shock loading in Ta are presented. Electron back-scatter diffraction (EBSD) examination of the damage evolution in sweeping-detonation-wave shock loading to study spallation in Cu is also presented.