The prevention of excessive deformation by thermal ratcheting is important in the design of high-temperature components of fast breeder reactors (FBR). This includes evaluation methods for a new type of thermal ratcheting caused by an axial traveling of temperature distribution, which corresponds to moving-up of liquid sodium surface in startup phase. Long range traveling of the axial temperature distribution brings flat plastic deformation profile in wide range. Therefore, at the center of this range, residual stress that brings shakedown behavior does not accumulate. As a result, repeating of this temperature traveling brings continuous accumulation of the plastic strain, even if there is no primary stress. In contrast, in the case with short range traveling, residual stress is caused by constraint against elastic part, and finally it results in shakedown. Because of this mechanism, we supposed that limit for the shakedown behavior depends on distance from the elastic part (i.e. half length of region with plastic deformation). In this paper, we examined characteristics of the accumulation of the plastic strain caused by realistic heat transients, namely, traveling of temperature distribution synchronizing with temperature rise. This examination was based on finite element analyses using elastic-perfectly plastic material. As a result, we confirmed that the shakedown limit depends not on the traveling range of the temperature distribution but the plastic deformation range, which was predicted by the elastic analysis. In the actual application, we can control the plastic deformation range by changing rate of the moving-up of liquid sodium surface.
The weld pass sequence generally affects residual stress profiles. In this study, the residual stress profiles of bead on plate specimens were analytically and experimentally examined. The material used in this study was the low alloy steel SQV2A (JIS G 3120), which is equivalent to ASTM A533. Phase transformation usually occurs around the welded area in SQV2A and also affects the residual stress profiles. To estimate residual stress, three specimens were fabricated. One was single pass bead welded and the others were five pass and nine pass bead welded. To predict the residual stress profiles numerically, temperature history analyses and residual stress analyses were conducted. Phase transformation strain was taken into consideration as a component of thermal strain. Analysis results show that the amount of longitudinal tensile stress at the center of the last pass area is lower than that at the edges. The longitudinal residual stress profiles around the last pass area of the five pass and nine pass specimens are similar to that around the weld pass area of the single pass specimen. The longitudinal tensile stress in the previous passes area is higher than that at the center of the last pass in the five pass and nine pass specimens. These analysis results suggest that the phase transformation strain affects the residual stress profiles around the last pass area in each specimen. To validate the analysis results, residual stress of these specimens were measured by using the strain relief method. The analysis results with the phase transformation strain consideration are in agreement with the experiment results. Accordingly, these analysis results can be considered valid.
An iodine-sulfur process based thermochemical water-splitting (IS process) for hydrogen production has been developed by JAEA as application of a high-temperature gas cooled reactor. The IS process includes a severe corrosion environment which is made to boil and decompose concentrated sulfuric acid. Two kinds of brittle materials, SiC, Si3N4 and Fe-high Si alloy, were reported as materials having enough corrosion resistance in this corrosion environment. The hybrid tube consisting of the Fe-high Si alloy with boiling sulfuric acid-resistant and the carbon steel with the ductility was produced by a centrifugal casting. An evaluation of the characteristics was carried out by hardness measurements, corrosion tests and thermal cyclic tests. The configuration of the hybrid tube by the centrifugal casting was 240 mm in outer diameter, 200 mm in inner diameter and 980 mm in length. The inner layer of the Fe-high Si alloy and the outer layer of the carbon steel stuck at the interface without pores. There is no intermetallic compound at the interface between the carbon steel and the Fe-high Si. The Fe-high Si alloy lining showed enough corrosion resistance in boiling concentrated sulfuric acid. Thermal cyclic tests (100-900 °C) were executed in order to evaluate the interface between the carbon steel and the Fe-high Si alloy. There was no detachment of the interface though the groove and the cracks were generated in the vicinity of the interface by thermal cycling. It is believed that the cracks parallel to the interface is attributed to the tensile stress during the heating process of thermal cyclic test and the flake graphite precipitate on the grain boundary. It was confirmed that the interface possessed the enough strength.
In existing severe accident codes such as MELCOR and THALES2, rupture of reactor pressure vessel (RPV) by relocated molten core is judged using simple models such as temperature and/or stress criteria. However, it is difficult to assess rupture behavior of the lower head of RPV in boiling-water-type nuclear power plants due to severe accident like Fukushima Daiichi. One reason is that boiling water reactors (BWRs) have geometrically complicated structure with a lot of penetrations. Another one is that BWR lower head is composed of various types of materials of RPV, weld-overlay cladding, control rod guide tubes, stub tubes, welds, etc. Therefore, we have been developing an analysis method to predict time and location of RPV lower head rupture of BWRs considering creep damage mechanisms based on coupled analysis of three-dimensional thermal-hydraulics (TH) and thermal-elastic-plastic-creep analyses. The detailed three-dimensional model of RPV lower head with control rod guide tubes, stub tubes, and welds are constructed. TH analysis is performed to obtain three-dimensional temperature distribution in relocated debris. Using TH analysis results, structural analysis is carried out to evaluate creep damage distributions using four types of damage criterions of “considere”, strain, Kachanov, and Larson-Miller-parameter (LMP) criteria. Creep damage evaluation based on Kachanov and LMP models is made by using experimentally determined parameters. From comparison of damage criterions, it is shown that failure regions of BWR lower head are only penetrations under simulated conditions, although there is a large difference in failure time.
A safety assessment needs to be conducted to analyze the damage caused by an aircraft impacting into a concrete structure at a nuclear power plant. One of the analytical methods used for this issue is a numerical impact simulation conducted after aircraft and reinforced concrete (RC) models are determined. We established the RC model and aircraft model in this study and confirmed the applicability of an impact simulation. Validation of our RC model was confirmed by conducting impact simulations of an F4 Phantom engine (GE-J79) crashing into three different wall thicknesses of 900, 1150, and 1600 mm. The damages to the wall in the simulations agreed with the test results conducted at Sandia National Laboratory around 1990. We also conducted parametric impact simulations of a rigid missile crashing into a concrete wall, changing the impact speed, mass of the missile, and the wall thickness. The wall thickness required to prevent perforation in the simulations was close to that estimated by the empirical formulae, although the residual speeds of the missile after the perforation in simulation did not agree very well to the values obtained by empirical formulae. One of the reasons of the difference in the residual speed is that the speed of the ejected concrete was not considered in our RC model. An impact simulation of an F4 Phantom crashing into a RC wall was conducted for the validation of our aircraft model. The shape of the impact load and the state of the frames of F4 Phantom on impact were almost the same as those in the test results conducted at Sandia, which showed that the F4 Phantom model was valid.
It is important to investigate the failure mode and ultimate strength of piping components in order to evaluate the seismic integrity of piping. Many failure tests of thick wall and high pressure piping for Light Water Reactors (LWRs) have been conducted, and the results suggest that the failure mode that should be considered in the design of a thick wall piping for LWRs under seismic loading is low cycle fatigue. On the other hand, Sodium cooled Fast Reactors (SFRs) is thin wall when compared to LWRs piping. Failure tests of a thin wall piping are necessary because past failure tests for LWRs piping are not enough to discuss failure behavior of a thin wall piping. Therefore, this present work investigated the failure mode and the ultimate strength of thin wall tees.
A new method has been developed to assess potential challenges by forest fire smoke on a cooling function of a decay heat removal system (DHRS) of a sodium-cooled fast reactor. Combinational numerical simulations of a forest fire propagation and a smoke transport were performed to evaluate a cumulative amount of smoke captured on air filters of the DHRS. The forest fire propagation simulations were performed using FARSITE code to evaluate a temporal increase of a forest fire spread area, a frontal fireline location, reaction intensity, and fireline intensity. Peripheral boundary of the forest fire spread area is shaped like an ellipse on the terrain, and the active forest fire area from which smoke is produced as a forest fire product is increased with forest fire spread. The smoke transport simulations were performed using ALOFT-FT code where a spatial distribution of smoke density, especially of particle matter (PM), is evaluated. The snapshot (i.e. at a certain time step) outputs by FARSITE on the reaction intensity and the fireline intensity were utilized as the input data for ALOFT-FT, while it was conservatively assumed that the smoke generated from the active forest fire area along the periphery boundary rises up from the frontal fireline location nearest to a nuclear power plant (NPP) and that prevailing wind transports all smoke to an NPP in the leeward side. The evaluated time-dependent changes of spatial PM density were utilized to calculate a cumulative amount of PM captured on the air filters of the DHRS. Sensitivity analysis was performed on prevailing wind speed to which both the fireline intensity and the smoke transport behavior are sensitive. The total amount of PM on the air filters was conservatively estimated around several hundred grams per m2 which is well below the utilization limit.
In a probable scenario for core disruptive accidents of Sodium-cooled Fast Reactors (SFRs), it is foreseen that molten core material would be discharged into lower sodium plenums through control rod guide tubes. Such material relocation might lead to a considerable thermal load on lower structures of the reactor vessels, while it has been suggested that in SFRs, as soon as the molten core material is discharged into coolant, it might be fragmented into smaller particles by fuel-coolant interactions and thus efficiently cooled in the reactor vessels. Hence, understanding of the fragmentation is crucial for achieving in-vessel retention of molten core material in SFRs. In this paper, based on the experimental results of a series of fragmentation tests, where around 10 kg of molten alumina (Al2O3) was discharged into a sodium pool (depth: 1.3 m, diameter: 0.4 m, temperature: 673 K) through a duct (inner diameter: 40mm to 63 mm) by using an experimental facility at National Nuclear Center of the Republic of Kazakhstan, dominant mechanisms for the fragmentation are discussed. In the present tests, mass median diameters of solidified Al2O3 particles were around 0.3 mm, which were comparable to the values predicted using conventional hydrodynamic-instability theories. However, even though the conventional theories predict that particle size becomes smaller with the increase of Weber number, such tendency was not observed in the present tests. Taking into account that in the present tests, the distances for fragmentation of molten Al2O3 were evaluated to be approximately 60 % to 70 % below the values predicted using an existing representative correlation which regards hydrodynamic instabilities as a dominant fragmentation mechanism, the observed independence on Weber number confirms a mechanism that before hydrodynamic instabilities sufficiently grow to induce fragmentation, thermal phenomena such as local coolant vaporization and resultant vapor expansion significantly accelerate fragmentation in SFRs.
Approximately two months after the Fukushima nuclear accident, the Japan Atomic Energy Agency (JAEA) led off a series of demonstration tests to develop effective but easily applicable decontamination methods for various school facilities in Fukushima. This effort included (1) dose reduction measures in schoolyards, (2) purification of swimming pool water, and (3) removal of surface contamination from playground equipment. Through these demonstration tests, they established practical methods suitable for each situation: (1) In schoolyards, dose rates were drastically reduced by removing topsoil, which was then placed in 1-m-deep trenches at a corner of the schoolyard. (2) For the purification of pool water, the flocculation coagulation treatment was found to be effective for collecting radiocesium dissolved in the water. (3) Demonstration tests for playground equipment, such as horizontal bars and a sandbox wood frame indicated that the decontamination effectiveness considerably varied depending on the material, paint or coating condition of each equipment piece. These findings were summarized in reports, some of which were compiled in local/national guidelines or handbooks for decontaminating the living environment in Fukushima.
The decommissioning of a nuclear facility is a long term project, handling information which begins from the design, construction and operation. Moreover, the decommissioning project is likely to be extended because of the lack of the waste disposal site especially in Japan. In this situation, because the transfer of knowledge and education to the next generation is a crucial issue, integration and implementation of a system for knowledge management is necessary in order to solve it. For this purpose, the total system of decommissioning knowledge management system (KMS) is proposed. In this system, we have to arrange, organize and systematize the data and information of the plant design, maintenance history, trouble events, waste management records etc. The collected data, information and records should be organized by computer support system e.g. data base system. It becomes a base of the explicit knowledge. Moreover, measures of extracting tacit knowledge from retiring employees are necessary. The experience of the retirees should be documented as much as possible through effective questionnaire or interview process. The integrated knowledge mentioned above should be used for the planning, implementation of dismantlement or education for the future generation.
Laser cutting conditions for steel plates having a thickness of more than 100 mm using a 30kW fiber laser were studied for the application to the nuclear decommissioning. Specimens of carbon steel and stainless steel plates were irradiated by laser beam and assist gas. The observed kerf widths at the rear face of the plates were considerably enlarged compared with those at the front face with the increase of the plate thickness for both specimens, when the stand-off distance between nozzle tip of the laser head and the specimen surface was kept 5 mm. Both kerf widths became comparable when specimens were cut at a relatively larger stand-off distance, where the incident laser beam size at the front face of the specimen was enlarged because of the defocusing of the beam. The results were applicable to the thick plate cutting, and specimens of stainless steel and carbon steel having a thickness of more than 100 mm were successfully cut based on this setup. The results show that for a very thick plate, sufficiently large kerf width was required for the cutting which was used as a duct for a successful melt flow process. The results are informative for the development of the laser cutting technology, and show that the laser cutting technology is promising for the dismantlement of thick steel components for the nuclear decommissioning.
The deep understanding of transient pool boiling critical heat flux (CHF) phenomena with treated surface and its correlation in water at saturated and subcooled conditions are becoming increasingly important for the database for the further enhancement of the design of liquid cooling technologies. Transient CHF using horizontal cylinders with different surfaces have been reported. However, there is a need to find the effect of surface wettability (contact angle) on transient CHF. This paper aims to study the steady and transient CHF due to exponentially increasing heat inputs, Q = Q0exp(t/τ) , using horizontal vertically oriented platinum ribbon in a pool of water with respect to pressure, subcooling, surface roughness and contact angle. The exponential period, τ, was varied from 5 ms to 10 s. We used three ribbon heaters with different surfaces, namely, commercial surface (CS), treated surface I (TS-I) polished by buff paper together with alumina, and treated surface II (TS-II) finished by emery paper. For the surface condition, surface roughness and contact angle of each ribbon were measured prior to pool boiling experiment. The acquired non-boiling heat transfer, steady and transient CHF were evaluated with existing corresponding equations. The steady-state CHFs measured on the TS-I were tested with the corresponding results of commercial surface. The three groups of transient CHF with different physical mechanisms, the enhancement of transient CHF in light of surface condition and transient CHF degradation depending on pressure and subcooling were reported.
Natural convection heat transfer from vertical rod bundles in liquid sodium was numerically analyzed for three types of the bundle geometry (two parallel, equilateral triangle and equilateral square arrays). The unsteady laminar three dimensional basic equations for natural convection heat transfer caused by a step heat flux were numerically solved until the solution reaches a steady-state. The PHOENICS code was used for the calculation considering the temperature dependence of thermo-physical properties concerned. The 2 to 4 test rods for diameter (D=7.6 mm), heated length (L=200 mm) and L/d (=26.32) were used in this work. The surface heat fluxes for each cylinder were equally given for a modified Rayleigh number, Rf,L, ranging from 3.06×104 to 3.14×107 (q=1×104 to 7×106 W/m2) in liquid temperature (TL=673.15 K). The values of S/D, which are ratio of the diameter of flow channel for bundle geometry to the rod diameter, for the rod bundle were ranged from 1.4 to 3 on each bundle geometry. The spatial distributions of local and average Nusselt numbers, Nuθ,z and (Nuav,B)N, on vertical rods of a bundle were clarified. The values of average Nusselt number, (Nuav,B)N,S/D, for three types of the bundle geometry with various values of S/D were calculated to examine the effect of the bundle geometry, S/D and Rf,L on heat transfer. The bundle geometry for the higher (Nuav,B)N value under the condition of S/D=constant was examined. The correlation for (Nuav,B)N,S/D for three types of bundle geometry above mentioned including the effects of Rf,L and S/D were developed. The correlations can describe the theoretical values of (Nuav,B)N,S/D for three types of the bundle geometry for S/D ranging from 1.4 to 3 within -7.44 to 10.73 % difference.
A district heating system for household heating and road snow melting utilizing waste heat from Gas Turbine High-Temperature Reactors of 300 MW (GTHTR300s), a high-temperature gas-cooled reactor design, was analyzed. The application area was set in Sapporo and Ishikari, cities with heavy snowfall in northern Japan. The heat transport analyses were performed by modeling heat-transfer components in the system to estimate the system's overall heat supply profile. These components included the pipelines of the secondary water loops between the GTHTR300s and the heat-application area; heat exchangers to transfer the heat from the secondary loops to the tertiary water loops of the district-heating pipes; and the district-heating pipes of the tertiary loops between the heat exchangers and houses and roads. Single- and double-pipes for the secondary loops were compared. Although the double-pipes were advantageous for having less heat loss and a smaller excavation area, these advantages did not compensate for the higher construction cost of the pipes. To satisfy the heat demand of the application area in the month of maximum requirement, 520-529 MW of heat were supplied by 3 GTHTR300s and delivered by 6 secondary loops, 3,450 heat exchangers about 90 m long, and 3,450 tertiary loops. More efficient designs for the heat exchangers and improvements to the tertiary loops applying branched flow networks are desired to reduce the number of heat exchangers and tertiary loops and to make the heat exchangers smaller. Heat lost to the ground from the tertiary loops comprised 80%-90% of the heat loss. Applications of the larger pipe or loops using the branched flow network or double-pipe are required for more efficient heat utilization. More than 90% of the construction cost went into thermal insulators. The thickness and properties of the insulator must be reevaluated for economical heat delivery.
When pressurized water or vapor leaks from a failed heat transfer tube in a steam generator of sodium-cooled fast reactors, a high-velocity, high-temperature jet with sodium-water chemical reaction may cause wastage on the adjacent tubes. For assessment of the wastage environment, a mechanistic computer code called SERAPHIM calculating compressible multicomponent multiphase flow with sodium-water chemical reaction has been developed. In this study, applicability of the SERAPHIM code was investigated through the analysis of the experiment on water vapor discharging in liquid sodium under actual condition of the steam generator. The computational domain consists of the cylindrical vessel and the simulated two horizontal heat transfer tubes. The cylindrical vessel was initially filled with liquid sodium. Pressurized water vapor goes into the sodium pool vertically upward from the discharging nozzle located at the center of one of the two tubes. The numerical result showed that the underexpanded jet appeared and impinged on the target tube located above the discharging tube. The calculated temperature distribution agreed with the measurement result well. The liquid droplet entrainment and its transport were considered in this analysis. The region with higher impingement velocity of the liquid droplet was close to the wastage region confirmed in the experiment.
In the last two decades, CFD codes have been widely used for the design studies of NPPs. Recently high-precision simulation models have been developed to evaluate complicated phenomena, e.g. fuel melting in severe accident. The authors also are developing a high-precision CFD code with an interface tracking method to simulate the gas entrainment (GE) phenomena in sodium-cooled fast reactors (SFRs), which might be caused by a highly-intensified free surface vortex. The GE in SFRs is characterized by an elongated interfacial dent along the vortex core and the bubble pinch-off at the tip of the dent. To simulate this complicated phenomenon, the authors’ CFD code has physics-basis algorithms which model accurately the interfacial dynamic behavior, the pressure jump condition at an interface and the surface tension. Several verification problems, e.g. the slotted-disk problem, have been already solved and the accuracy of each individual algorithm is confirmed. In this paper, a basic experiment of the GE is simulated to validate the developed CFD code. In the experiment, the entrained gas flow rate is measured by image processing with a high-speed video camera. The simulation result of the entrained flow rate shows comparable value to the experimental data, that is, our CFD code is considered applicable to the evaluation of the GE in SFRs.
In this paper, the fabrication method of the BP/C/C composites, and the effect of bamboo charcoal on the wear and friction properties were investigated. The matrix was phenol resin, and reinforcements were Bacterial Cellulose (BC) and Bamboo charcoal particles (BP) as Si additive. The effect of BP weight contents on wear and friction performance has been experimentally investigated. Samples were prepared by carbonizing at temperatures of 700°C to 1000°C. The wear tests were carried out by using pin on drum type wear testing apparatus for constant dry sliding conditions. From the experimental results of wear tests, the wear and friction properties of the BP/C/C composites were dependent on the content of BP wt% and carbonizing temperature. The composites with 5wt% BP carbonized at 900°C indicated the lowest friction coefficient of 0.14 among the composites. The composites with 5wt% BP carbonized at 1000°C exhibited the lowest wear rate of 2.25×10-10 [mm2/N]. Compared with the nano-C/C composites with BC and Phenol resin and the BP/C composites, the BP/C/C composites with optimum BP wt% at higher carbonizing temperature showed lower wear rate and friction coefficient. The experimental results indicated that bamboo charcoal can be applied as filler which can provide lower wear rate and friction coefficient.
Crystal orientations of creep damaged Type 316 stainless steel were measured by 10 organizations using the same specimens, passed in a round robin, in order to investigate the scatter in material damage assessment using the electron backscatter diffraction (EBSD) technique. The measurements were performed according to the EBSD measurement guideline issued by the Society of Material Science, Japan. Two misorientation parameters, the local and intra-grain misorientations, were calculated using mapping data of measured crystal orientations. It was shown that the area averaged local and intra-grain misorientations correlated well with the degree of the inelastic strain caused by the creep damage. Although the area averaged local misorientation showed eminent scatter, the scatter in the area averaged intra-grain misorientation was relatively small. The scatter in the area averaged local misorientation was deduced to be brought about by the error in the crystal orientation measurements. Since the accuracy of the crystal orientation measurement depends on various factors and is difficult to control, the correlation between the degree of the creep damage and the local misorientations obtained by one SEM/EBSD system is difficult to apply to other SEM/EBSD systems. On the other hand, the area averaged intra-grain misorientation is not affected much by the error in the crystal orientation measurements and the values obtained by various organizations using different SEM/EBSD systems were almost the same. It was concluded that the area averaged intra-grain misorientation can be used for measurement of the creep damage (inelastic strain). The empirical relationship between the area averaged intra-grain misorientation and the degree of the creep damage can be shared regardless of the SEM/EBSD system used.
This work deals with time-dependent creasing characteristics of coated paperboard. The knowledge of dynamic bending moment (resistance) acting on a hinge which is folded onto a creased line, is important in order to adjust a few of boxing condition. The correlation between the dynamic bending resistance and several primary problems such as the time-dependent residual strains on actual processing phenomenon was not sufficiently discussed in the past. It is difficult to estimate various time-dependent responses from a quasi-static initial stiffness of a creased part, such as the maximum peak bending moment and the gradient of bending moment. Therefore, a prototype Crease Stress Tester (CST) has been applied to seek the dynamic bending moment and its residual deformation. In order to reveal the relaxation characteristics of bending angle during the folding and returning back motion from a tracking angle of 90°, a white-coated paperboard of 0.3 mm thickness was scored with a creaser knife and a grooved face counter plate under a specified feed velocity, and then the bending and release test was carried out up to the second round folding under a couple of indentation depth of crease forming (nominal shear strain). Through this work, the followings were found: (1) The release response of folded angle during returning back was characterized and approximated by a logarithmic function of elapsed time; (2) The release of folded angle depends on the bending rotation velocity.
This paper describes creep-fatigue lives of Sn-3.5Ag lead-free solder at low temperatures. Since solders have lower melting temperature and electronic devices are often used at low temperature environment, it is effective for improving the fatigue life evaluating precision of solder joints to make clear the mechanical properties and creep-fatigue properties of solders at low temperatures. Cyclic push-pull fatigue tests with various strain waveforms were conducted at 253K and 273K to examine influence of strain rate and testing temperature on fatigue life of Sn-3.5Ag lead-free solder. Creep-fatigue lives under unsymmetrical full reversed strain waveform were smaller than that of symmetrical waveform at low temperatures. An application of five kinds of creep-fatigue life evaluation parameters for electronic materials at low temperatures was also discussed. They are Linear Damage Rule, Frequency Modified Fatigue Life, Ductility Exhaustion Model, Strain Range Partitioning method and Grain Boundary Sliding Model. Grain Boundary Sliding Model, which has been proposed as a fatigue life evaluation parameter for Pb-content solders and lead-free solders at high temperatures, was a suitable parameter for the correlation of creep-fatigue lives of Sn-3.5Ag lead-free solder at low temperatures. Grain Boundary Sliding Model parameter predicted almost all of the experimental lifetimes within a small scatter conservatively.
Huge amount of CVD-diamond coated milling tools were used for machining of CFRP and CFRTP sheets and blocks in the airplane and automotive industries. Because of chipping and tooth-tip damage in the diamond coatings during those dry machining processes, the tools must be exchanged with new ones to preserve the geometric accuracy in practice. WC (Co) substrate in these used tools had to be recycled to lower the production cost; reliable ashing process was necessary to remove only the used diamond coatings without significant damages even to the tooth tip of substrate. Furthermore, fast-rate ashing became a key to shorten the leading time for exchange of milling and drilling tools. High density oxygen plasma ashing method with use of the hollow cathode device was proposed to remove the used diamond coating with the film thickness of 10 μm. Both the emissive-light optical spectroscopy and the Langmuir probe method were employed to make quantitative diagnosis on the generated oxygen plasmas. The average ion density increased up to more than 1x1017 m-3, higher than the conventional plasma states by one order. Activated oxygen atom had overwhelming population among the generated species in this high plasmas density. This high density oxygen flux was responsible for complete and fast-rate removal of CVD diamond coating; e.g. the average ashing rate turned to be more than 10 μm/hour. The short-shank, end-milling tools were employed to describe this ashing behavior with time. Corresponding to the variation of CO-peak intensity in the measured spectra by on-line spectroscopy, the diamond film thickness reduced monotonically with time up to 3.6 ks. The removal rate gradually decreased with time in the final stage. Fine tuning of oxygen plasma processing conditions was capable to reduce the damage depth of tool teeth tips down to 1 μm, significantly less than the standard tolerance of 5 μm.
This paper describes stress analysis of SS400 natural rubber (NR)-bonded structures, assuming large deformation, applying the finite element method. We first carried out a comparison of the stress components σθθ and τrθ for each singular point for width of adhesive w = 30 mm. Next, a stress analysis was performed on SS400 NR-bonded structures using the delamination force previously obtained by delamination testing. Finally, the intensity of the stress singularity, Kθθ, obtained from a geometrically nonlinear analysis, i.e., large deformation analysis for linear elasticity, and geometrically nonlinear analysis considering material nonlinearity, i.e., large deformation analysis for hyperelasticity, were evaluated using several computational models while varying the width of the adhesive.
A novel reliability-based approach has been developed for multi-state engine systems. Firstly, the output power of the engine is discretized and modeled as a discrete-state continuous-time Markov random process. Secondly, the multi-state Markov model is established. According to the observed data, the transition intensity is determined. Thirdly, the proposed method is extended to compute the forced outage rate and the expected engine capacity deficiency based on time response. The proposed method can therefore be used for forecasting and monitoring the reliability of the multi-state engine utilizing time-domain response data. It is illustrated that the proposed method is practicable, feasible and gives reasonable prediction which conforms to the engineering practice.
The chest compression is one of the most important actions for first-aid cardio-pulmonary resuscitation (CPR). Since it requires large torque/force to be generated, the performers have to take an energy saving position and motion until advanced life support providers take over. In the basic life-saving certification, an expert demonstrates the chest compression and trainees behave like him. However, since the energy saving motion strictly depends on the body weight and height of the performers, an appropriate indication and instruction for the trainees will be necessary. In this paper, we optimize the chest compression from kinematic, dynamic and temporal point of view. By using Pseudo-differential and zero-phase filter, the angular velocity and acceleration are derived from a motion capture data, and generative force is calculated by inverse dynamic computation. Based on an evaluation function and constraints, the chest compression is optimized kinematically, dynamically and temporally. Moreover, for the chest compression of a child with light weight, a motion aid is optimized. The effectiveness of the proposed method is evaluated based on a physical load of the performers by measuring heart rate.