Time Tf Research Articles

Kinetics Study on the Modification Process of Al2O3 Inclusions in High-Carbon Hard Wire Steel by Magnesium Treatment

The aim of the experiment in this work is to modify the Al2O3 inclusions in high-carbon hard wire steel by magnesium treatment. The general evolution process of inclusions in steel is: Al2O3 → MgO·Al2O3(MA) → MgO. The unreacted core model was used to study the modification process of inclusions. The results show that the complete modification time (tf) of inclusions is significantly shortened by the increase of magnesium content in molten steel. For Al2O3 inclusions with radius of 1 μm and Mg content in the range of 0.0005–0.0055%, the modification time of Al2O3 inclusions to MA decreased from 755 s to 25 s, which was reduced by 730 s. For Al2O3 inclusions with a radius of 1.5 μm and Mg content in the range of 0.001–0.0035%, the Al2O3 inclusions were completely modified to MgO inclusions from 592 s to 55 s. The Mg content in the molten steel increased 3.4-fold, and the time for complete modification of inclusions was shortened by about 10-fold. With the increase of Al and O content in molten steel, the complete modification time increased slightly, but the change was small. At the same time, the larger the radius of the unmodified inclusion is, the longer the complete modification time is. The tf of Al2O3 inclusions with a radius of 1 μm when modified to MA is 191 s, and the tf of Al2O3 inclusions with a radius of 2 μm when modified to MA is 765 s. According to the boundary conditions and the parameters of the unreacted core model, the MgO content in inclusions with different radius is calculated. The experimental results are essentially consistent with the kinetic calculation results.

Performance Analysis of CMOS Circuits using Shielded Channel Dual Gate Stack Silicon on Nothing Junctionless Transistor

In this paper it has been demonstrated that a shielded channel made by varying the side gate length in silicon-on-nothing junctionless transistor not only improves the short channel effect but also improve the performance of CMOS circuits of this device. The proposed device shielded channel dual gate stack silicon on nothing junctionless transistor (SCDGSSONJLT) drain induced barrier lowering (DIBL), cut-off frequency and subthreshold slope are improved by 20%, 39% and 20% respectively over the single material gate silicon on insulator junctionless transistor (SMG SOI JLT). The proposed device CMOS inverter fall time Tf (pS) and noise margin improves by 50% and 10% compare to shielded channel silicon on insulator junctionless transistor (SCSOIJLT). It has been observed that circuit simulation of CMOS inverter, NAND and NOR of proposed device. The static power dissipation in the case of proposed SCDGSSONJLT device are reduced by 45%, 81% and 83% respectively over the SMGSOIJLT. Thus, significant improvement in DIBL, cut-off frequency, propagation delay and static power dissipation at low power supply voltage shows that the proposed device is more suitable for low power CMOS circuits.

Immobilization of horseradish peroxidase onto electrospun polyurethane nanofiber matrices

AbstractIn this work, horseradish peroxidase (HRP) was immobilized onto polyurethane nanofiber membranes. The following variables were optimized to maximize the surface density of grafted HRP (Q): NaClO functionalization time (tf), immobilization time (ti), HRP concentration of the immobilization solution (CHRP), and immobilization temperature (T). Catalytic activity was evaluated using the decolorization reaction of Orange II (OII). A statistical analysis of SEM images demonstrates that fiber diameters (d) of native (M), AGE‐modified (MA), and HRP immobilized (MAH) electrospun membranes obeyed a log‐normal distribution and that the effects of the NaClO activation procedure, and the use of MAH membranes in OII oxidation during 4 h on the fiber size were negligible. Although obtained membranes at 40°C (MAH9540) presented the highest Q, matrices obtained at 20°C (MAH9520) exhibited the highest catalytic activity, indicating that HRP was partially inactivated during the immobilization at 40°C. Reusability tests demonstrated that membranes retained between 11% and 33% of their initial enzyme activity after a total reaction time between 4 and 8 h.

Evaluation of the Effect of Continuous Infusion of Dexmedetomidine or a Subanesthetic Dose Ketamine on Transcranial Electrical Motor Evoked Potentials in Adult Patients Undergoing Elective Spine Surgery under Total Intravenous Anesthesia: A Randomized Controlled Exploratory Study.

Study DesignProspective, randomized, placebo-controlled, double-blind exploratory study.PurposeTo compare effects of dexmedetomidine or a subanesthetic dose of ketamine on the amplitude and latency of transcranial electrically generated motor evoked potentials.Overview of LiteratureTotal intravenous anesthesia (TIVA) is a standard anesthesia technique for transcranial electrical motor evoked potential monitoring in spine surgery. We aimed to determine whether the use of dexmedetomidine and ketamine as a component of TIVA exerted any beneficial effect on the quality of monitoring.MethodsA total of 90 American Society of Anesthesiologist grade I–III patients, aged 18–65 years, with a motor power of ≥4/5 grade as per the Medical Research Council Scale in all four limbs who were scheduled for elective spine surgery under transcranial electrical motor evoked potential monitoring were enrolled. The subjects were randomly allocated into the following three groups: group PD who received 0.5 μg/kg/hr dexmedetomidine infusion, group PK who received 0.5 mg/kg/hr ketamine infusion, and group PS who received normal saline infusion, along with standard propofol–fentanyl based TIVA regime. Amplitude and latency of bilateral motor evoked potentials of the tibialis anterior and abductor halluces muscle were recorded at Ti (at train-of-four ratio >90%), T30 (30 minutes post-Ti), T60 (60 minutes post-Ti), and Tf (at the end of spine manipulation).ResultsBaseline median amplitudes were comparable among the study groups. In group PK, we noted a gradually enhanced response by 24%–100% from the baseline amplitude. The median amplitudes of all the muscles were higher in group PK than those in groups PS and PD at time points T60 and Tf (p<0.05).ConclusionsThe present study demonstrated that compared with dexmedetomidine and control treatment, a subanesthetic dose of ketamine caused gradual improvement in amplitudes without affecting the latency.

Integration of multi-objective reliability-based design optimization into thermal energy management: Application on phase change material-based heat sinks

Phase change material-based heat sinks are widely used in several industrial applications such as in the field of industrial automation and mechatronics. Nowadays, several researchers aim to obtain an optimal design of these systems in order to ameliorate its performances. Nevertheless, uncertainties are not considered for the majority of these studies. Furthermore, it has been confirmed that deterministic multi-objective optimization (DMOO) may lead to an unreliable design. In this study, a new methodology that leads to perform the Multi-Objective Reliability-Based Design Optimization (MORBDO) for thermal management of a passive cooling system is proposed. It consists in coupling the Finite Element Model (FEM), MORBDO procedures and surrogate approaches. Kriging predictor is used to construct metamodels and then validated using Cross-Validation (CV) and error predictions. A numerical investigation is carried out to study the different DMOO and MORBDO approaches. In this study, a 3D PCM-based round pin-fin heat sink is detailed. The aim of this problem is to minimize two objective functions: the cost (total volume V) and the final cooling time tf by considering both thermal and physical constraints. For this purpose, geometrical uncertain parameters are considered such as length L, height H and ϕ pin diameter of the heat sink. This study leads to develop a well-distributed reliable Pareto solutions by combining the Robust Hybrid Method (RHM) and the Constrained Non-dominated Sorting Genetic Algorithm (C-NSGA-II). Then, the efficiency of the proposed MORBDO-RHM approach for PCM-based heat sink is verified.

The Relationship Between Maximum Jump Performance and Force-time Variables of Block Landing Skill in Junior Elite Volleyball Players

Purpose: Frequent and powerful jumps and landings in volleyball exert significant stresses on lower extremities which can be determinant of injury prevalence. This study aimed to investigate the possible correlation between Maximum Jump (MJ) performance and force-time variables of volleyball block landing. Methods: Thirty elite junior volleyball players (Mean±SD of age: 18.140±1.125 y, sports background: 4.390±0.957 y, and height: 197.100±3.161 cm) performed three block jumps, and best of trials was considered for further analysis. The study data were collected by the KISTLER force platform (1000 Hz). Force-time, velocity-time, and displacement-time were obtained using the Excel program. The Kolmogorov-Smirnov and Pearson correlation coefficient were used for assessing data normality and possible correlations between variables using SPSS v. 21 (P&lt;0.05). Results: Peak vertical impact forces were reported in a range of 1.8-3.5 BW (F1, F2) during 27 to 83 ms of peak times (T1, T2). Significant positive correlations were obtained between temporal variables of time of peaks (T1, T2), the time elapsed between peaks (TP), and end of landing time (Tf). A significant negative correlation was found between F2 and T2 and a significant positive correlation between MJ performance with peak vertical forces (F1, F2). Conclusion: According to the findings, T1 has little impact on shock absorption. Coaches and volleyball players should consider the importance of soft landing through increasing T2, which decreases F2, not only for performance improvement but also for reducing injuries.

Analysis of Gas–Liquid–Solid Three-Phase Flows in Hydrocyclones Through a Coupled Method of Volume of Fluid and Discrete Element Model

Abstract Liquid–gas–solid three-phase flows in hydrocyclones are studied numerically in this paper by employing a coupled method of the volume of fluid (VOF) and discrete element model (DEM) with Reynolds stress model (RSM) turbulence model. The numerical method is validated by comparing the calculated results to those of experiments published in the literature about the separation of particle flows in hydrocyclones. Since VOF-DEM model could capture the gas–liquid interface of particle flows, the three-dimensional formation process of the air-core together with the formation of the spiral trajectory of particles are depicted for the first time. In addition, the effects of the particle concentration ω (less than 12%) on the air-core formation time Tf and diameter Da are studied systematically, which has not been reported in the literature. The increase of ω has both positive and negative actions on the change of Tf and Da, and the compromises of two kinds of actions generate the valley or peak of the curves of Tf versus ω and Da versus ω, respectively. Moreover, the results for three hydrocyclones with different cone angles are also compared to study the effects of the cylindrical and conical section on the air-core formation and the separation performance of the hydrocyclones. By analyzing the flow fields and the pressure changes inside the hydrocyclones, qualitative explanations of the relevant discoveries are given in this paper. The results will be helpful in the investigation of the multiphase flow behaviors in the hydrocyclone and in the selection of the appropriate hydrocyclone.

Study on driving waveform design process for multi-nozzle piezoelectric printhead in material-jetting 3D printing

Purpose Material-jetting (MJ) three-dimensional (3D) printing processes are competitive due to their printing resolution and printing speed. Driving waveform design of piezoelectric printhead in MJ would affect droplet formation and performance, but there are very limited studies on it besides patents and know-hows by commercial manufacturers. Therefore, in this research, the waveform design process to efficiently attain suitable parameters for a multi-nozzle piezoelectric printhead was studied. Therefore, this research aims to study the waveform design process to efficiently attain suitable parameters for a multi-nozzle piezoelectric printhead. Design/methodology/approach Ricoh’s Gen4L printhead was adopted. A high-speed camera captured pictures of jetted droplets and droplet velocity was calculated. The waveforms included single-, double- and triple-pulse trapezoidal patterns. The effects of parameters were investigated and the suitable ones were determined based on the avoidance of satellite drops and preference of higher droplet velocity. Findings In a single-pulse waveform, an increase of fill time (Tf) decreased the droplet velocity. The maximum velocity happened at the same pulse width, the sum of fill time and hold time (Tf + Th). In double- and triple-pulse, a voltage difference (Vd) above zero in the holding stage was adopted except the last pulse to avoid satellite drops. Suitable parameters for the selected resin were obtained and the time-saving design process was established. Research limitations/implications Based on the effects of parameters and observed data trends, suggested procedures to determine suitable parameters were proposed with fewer experiments. Practical implications This study has verified the feasibility of suggested design procedures on another resin. The required number of trials was reduced significantly. Originality/value This research investigated the process of driving waveform design for the multi-nozzle piezoelectric printhead. The suggested procedures of finding suitable waveform parameters can reduce experimental trials and will be applicable to other MJ 3D printers when new materials are introduced.

ACUTE EFFECTS OF DYNAMIC AND PNF STRETCHING ON LEG AND VERTICAL STIFFNESS ON FEMALE GYMNASTS

The purpose of the study was to investigate the acute effect of Dynamic (DS) and PNF stretching on leg (Kleg) and vertical stiffness (Kvert) on female gymnasts. Thirty-one female athletes from various types of gymnastics (artistic, rhythmic, team gymnastics) participated in this study ([Mean ± SD] age: 22.32 ± 3.35 years, height: 164.87 ± 4.96 cm, body mass: 57.20 ± 6.54 kg) performed 30 sec running bouts at 4.44 m *s-1, under 3 different stretching protocols (PNF, DS, and no stretching [NS]). The total duration in each stretching condition was 6 minutes, and each of the 4 muscle groups was stretched for 40 seconds. Leg and vertical stiffness values were calculated using the “sine wave” method. No significant influence of stretching type on Kleg and Kvert were found after DS and PNF stretching. However, significant changes were found in Fmax, Dy, flight time (tf), step rate (SR), and step length (SL) after DS and PNF stretching protocol, indicating that DS produced greater changes compared to PNF protocol.

Lightning Impulse Long Delay Breakdown of Centimeter Vacuum Gaps

This paper presents an experimental investigation into the breakdown voltage fall time tf of lightning voltage breakdown of 2-4 centimeter vacuum gaps having a long breakdown delay time td(>30 μs). The results show that the average 50% breakdown voltage fall time t50 decreases with increasing vacuum gap. It is considered that the lightning impulse breakdown of the centimeter vacuum gaps with a long breakdown delay time may be initiated by the interaction between the cathode thermal processes and the micro-particles phenomena. The increase of the electrode diameter and the decrease of the electrode radius of curvature may contribute to the decrease of the breakdown voltage fall time.

Tin-manganese-nickel oxide thin films prepared by thermal evaporation for photosensor applications

This study reports the synthesis and characterization of non-stoichiometric nanocrystalline Tin-Manganese-Nickel (Sn-Mn-Ni) oxide thin films prepared by thermal evaporation for photosensor applications. The photoconductive characteristics were investigated by fabricating a sandwich-structure device of p+-Si-substrate/Sn-Mn-Ni-oxide-thin-film/indium-tin-oxide (ITO). Results show that Sn37Mn10Ni53Ox thin films exhibit an absorption coefficient of 1.15 × 106cm−1in visible light spectrum. In additions, the device characteristics including a high responsivity (Rres) of 11.5 A/W, and the fast photo-response with a rise time (tr) of 41.2 ms and a fall time (tf) of41.6 ms measured at 1.0 V bias and 460 nm wavelength were obtained. Hence, the Sn37Mn10Ni53Ox thin film is favorable for potential photosensor applications in visible light spectrum.

Subcritical crack growth models for static fatigue of Hi‐NicalonTM‐S SiC fiber in air and steam

AbstractThree subcritical crack growth (SCG) laws were used to model strain‐rates and failure times for static fatigue of Hi‐NicalonTM‐S SiC fiber tows in air and Si(OH)4(g)‐saturated steam. Models were fit to tow failure times (tf) and steady‐state strain rates (ἑ) for brittle creep measured at 700 to 1100°C under initial applied stresses (σA) of 260 to 1260 MPa. A power law, a reaction‐rate law, and a bond‐energy law were used to describe SCG that caused sequential filament failure, and ultimately tow failure. Two versions of each model were developed. One allowed access of chemisorbed species to flaws throughout the fiber (mode 1) and another only allowed access to flaws at the SiC‐SiO2 interface (mode 2). The stress increase on intact filaments as others fractured and as filaments oxidized, and the increase in stress intensity geometric factors (Y) as crack size increased were incorporated in the models. The fits to data were compared for the different models by using both simple regression analysis and orthogonal distance regression (ODR) analysis. Faster convergence and more consistent results were achieved using ODR analysis. Regression analyses found parameters for all models with similar error in data fits, so validity of a model could not be distinguished by regression analysis alone. For all models, the stress dependence of SCG rates was much stronger in steam than in air, and for most models activation energies were between 300 and 420 kJ/mol, regardless of environment. For the steam environment, the bond‐length parameter (δ) for the bond‐energy model was very close to the lattice parameter of β‐SiC (.436 nm), but in air it was significantly lower at 0.25‐0.26 nm, but still larger than the Si‐C bond length of 0.189 nm. Other factors suggest that either a bond‐energy based law or a modified version of a reaction‐rate law are the best choices for a SCG law. Filament strength distributions initially described by Weibull distributions could not be described by such distributions after application of the models. SCG mechanisms are discussed.

Experimental study and mechanism of bistable all-optical switching based on diarylethene-doped film

A method for constructing bistable all-optical switching based on the changes in the photoinduced-absorption characteristics of diarylethene-doped organic films is proposed. A doped organic film sample (10 wt.% doping concentration) was prepared by doping cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene diarylethene into polymethyl methacrylate using a 375-nm continuous wave (CW) laser (40 mW) and 532-nm laser (CW, 5 mW) as the pump beam and a 632.8-nm laser (CW, 3 μW) as the probe beam. The experimental results of the bistable all-optical switching effect of the thin-film sample were obtained. The modulation depth M of the switching signal was 8.2 %, the rise time tr of the switching was approximately 36 s, and the falling time tf was approximately 47 s. The influence of the change in the pump beam power on the switching signal was studied experimentally. Based on the photochromic two-level system, a theoretical model of the bistable all-optical switching signal changing with time was established, the mechanism of bistable all-optical switching was clarified, and the experimental results were analyzed. The nonlinear fitting results show that the experimental data are in good agreement with the theoretical model. This bistable all-optical switching is simple and easy to implement, and it has potential application value as a low-speed bistable all-optical switching method.

Characteristic of friction welding weld joint of AA6061 on elevated environmental temperature

Rotary Friction Welding is a solution in addressing the poblems in welding of material difficult to weld by fusion welding, such as AA6061 aluminium alloy. Fusion welding is difficult to apply to aluminium alloy because of porosity and crack which often occur during solidification. From the research on friction welding of AA6061, it can be conclude that excessive welding temperature of friction welding may result in thermal softening in weld zone and HAZ. The excessive cooling rate after friction welding run will affect to formation of hard and brittle of weld zone. Increase of environmental temperature above room temperature will accelerate workpiece to achieve solid state condition and lowering difference between weld peak temperature and inital weld temperature (ΔT) which mean decreasing of coooling rate. In this research, environmental temperature were varied of 27 °C (room temperature), 50 °C, 75 °C, 100 °C, 125 °C dan 150 °C. Some parameters are set constant such as rotation speed of 1600 rpm, friction pressure of 65 bar or 65 kg.cm−2, friction time (tf) of 6 seconds, forging pressure of 325 bar or 325 kg.cm−2, forging time of 60 seconds, contact diameter of workpiece of 15 mm and the workpiece chamfer angle of 15°. The contact area is divided into three zones, which are the plastic deformation zone (Zpl), the partial deformation zone (Zpd) and the non-deformed zone (Zud). The higher the environmental temperature will produces the wider plastic zone and plastic deformation zone (Zpl + Zpd). The higher the environmental temperature will causes the yield strength of the AA 6061 friction weld joint to increase which modelled as y = 3E-05x2 + 0.0033x + 16.582. Likewise, the tensile strength of the AA 6061 friction weld joint also increases which modelled as y = 3E-05x2 + 0.0026x + 18.119. When comparing the hardness of rotating workpiece side (spin) with workpiece side pressing (press), the previous one is higher at all variations of the temperature. From the photograph of the microstructure of base metal of Al 6061, dark particles (Mg2Si) and gray particles (Fe3SiAl12) are present in the Al matrix. The grain structure of Zud is bigger than Zpd and Zpl. Zpd microstructures at all environmental temperatures form smaller granular structures than base metal grains. Zpl microstructure in workpieces with environmental temperature of 27 °C, 50 °C, 75 °C and 100 °C were formed in small granular structure with Mg2Si (black) and Fe3SiAl12 (gray) structure which spread evenly. However Zpl microstructure with environmental temperature of 125 °C and 150 °C seems to enlarge, especially the structure of Fe3SiAl12 (gray), due to overheat and excessive softening.

Artificial aging heat treatment post-effect on profile and mechanical properties of the AA 6061 friction welding joint

Friction welding is a solution for metal joint problems that are difficult to joint with fusion welding. The quality results of friction welding are highly dependent on process parameters such as friction pressure, friction time, forging pressure, forging time, and rotating speed. There is often excessive softening, hardening of the metal grains, and formation of an intermetallic phase at the weld interface due to too high friction temperatures and too high forging pressures on the alloy. Several studies on AA 6061 concludes artificial aging heat treatment can provide positive changes on the tensile strength and microstructure of AA 6061. The purpose of this study is to find out the effect of post artificial aging treatment toward profile and mechanical properties of AA 6061 friction welding joint. The varied parameters are forging pressure in friction welding of 325 bar, 350 bar, 375 bar and artificial aging heating temperature post-welding of 100 °C, 150 °C and 200 °C. The fixed parameters observed are the connection profile, microstructure, hardness distribution and tensile strength of the joint. Controlled variables include: 1600 rpm spindle rotation, 65 bar or 65 kg cm−2 friction pressure, friction time tf = 6 seconds, time forging pressure tu = 60 seconds, workpiece contact diameter 15 mm and 15 degrees workpiece chamfer angle. The results are specimens with forging pressures of 325 bar, 350 bar and 375 bar without artificial aging treatment still show clearly interface of Zpl and Zpd zone; whereas in specimens treated with artificial aging, the Zpd and Zpl interface are getting faded which indicating that there is structures homogenization in the Zpd and Zpl zone. The hardness of the joint area increased significantly after artificial aging heat treatment because formed Mg2Si precipitates were dispersed in the Zpl, Zpd and Zud zones. The post-weld artificial aging heat treatment also resulted in a more even distribution of hardness in the joint area. The highest distribution of joint area hardness occurred in specimens with a forging pressure of 350 bar and artificial aging treatment at 200 °C. Artificial aging treatment with a temperature of 200 °C will form Mg2Si (black) precipitation and Fe3SiAl12 (gray) particles which are evenly dispersed in the Al matrix in the Zpd and Zpl zones so that their hardness is high. By applying artificial aging heat treatment, the tensile strength of the specimens increases until the artificial aging temperature is 150 °C; when the artificial aging temperature is raised to 200 °C, the tensile strength tends to drop back.

NUMERICAL INVESTIGATIONS OF FLUSHING TIME IN SMALL MARINAS

This paper presents the results of 2D and 3D numerical simulations of sea circulation and water mass exchange for a marina with hypothetical dimensions (L/B=2 and L/B=0.5) to calculate the return flow factor. The return flow factor b was analyzed in relation to the marina entrance width, sea current velocity outside the marina (0, 1, 2, and 5 cm/s) and the sea surface level oscillation dynamics. The basic comparative parameter is the e-flushing time, Tf. The intensity of forced circulation is calculated to achieve time Tf of less than 10 days. The impact of the wind field on the e-flushing time for different marina widths was analyzed using a 3D numerical model. The numerical simulation results indicate that the e-flushing time Tf depends on the amplitude of the tidal signal, secondary to the width of the marina inlet, and the smallest amount on the velocity field in the outer region. Conversely, the return flow factor b depends on the width of the marina entrance, less on the tidal signal amplitude, and least on the current velocity outside the marina if currents are ≥ 1 cm/s. Forced circulation of 1 m3/s is only required for the marina with a smaller tidal amplitude (position Dubrovnik) to achieve Tf&lt;10 days. If at the observed location wind is a dominant sea circulation generator, a wider marina entrance will allow faster sea exchange.

THE MINIMIZATION OF THE MEAN SQUARE OF THE DEVIATION OF A RANDOM SIGNAL FROM A GIVEN TARGET

In this paper we consider the problem of minimization of the mean square value of the deviation of a random signal z(tf ) from a given target ζ. The random signal z(tf ) represents the value at instant time tf of an output of a controlled dynamical system described by an Itˆo differential equation. Both the case when the set of admissible controls consist of general nonanticipative stochastic processes and the case when only piecewise constant controls are available are analyzed. We show that in both cases the optimal controls are in affine state feedback forms. Explicit formulae of the gain matrices of the optimal controls are provided.

THE MINIMIZATION OF THE MEAN SQUARE OF THE DEVIATION OF A RANDOM SIGNAL FROM A GIVEN TARGET

In this paper we consider the problem of minimization of the mean square value of the deviation of a random signal z(tf ) from a given target ζ. The random signal z(tf ) represents the value at instant time tf of an output of a controlled dynamical system described by an Itˆo differential equation. Both the case when the set of admissible controls consist of general nonanticipative stochastic processes and the case when only piecewise constant controls are available are analyzed. We show that in both cases the optimal controls are in affine state feedback forms. Explicit formulae of the gain matrices of the optimal controls are provided.

Correlation and diffusion breaking in the failure process of composite materials

Fiber bundle model is one of the important statistical and theoretical physics approaches to investigate the fracture and breakdown of heterogeneous material extensively used both by the engineering and physics community. In this paper, using the correlation function and its properties, we study the diffusion of the failure process in composite materials that consist of a set of with randomly oriented fibers loaded by an external constant total load. The investigation is based on fiber bundle model where the fibers are randomly oriented; each fiber is subject only the cosine component of the external load, and when it fails, its load is shared by surviving neighboring fibers according to the local load sharing rule (LLS). The failure process ensures an advancing interfacial fracture and the areas of the damaged regions increases with time until a final crack of material. By using the correlation function of the fraction of broken fibers, we study the diffusion properties of micro crack created in the composite materials. The results show that the correlation decreases exponentially with time and decreases with both of applied load and temperature. We calculate then the effective diffusion coefficient cracks which increase exponentially with applied load and linearly with the temperature. The failure time tf of the materials decrease with temperature as a power law. Obtained results are compared with the one of the classical model consist of a set of parallel fibers.

Development of a Pulsed Power Supply Utilizing 13 kV Class SiC-MOSFETs

To resolve the drawback of conventional thyratron switches, development of a semiconductor high voltage switch utilizing a 13 kV class SiC-MOSFET developed by Tsukuba Power Electronics Constellations (TPEC) is proceeding. At first, the device evaluation test was carried out with a resistive load circuit. With the conditions of drain voltage of 10 kV and load resistance of 1 kΩ, turn on loss Eon, turn off loss Eoff, rise time Tr and fall time Tf were 1.7 mJ, 1.1 mJ, 64 ns, and 75 ns, respectively. Thereafter, the 2s-12p switch array was designed and assembled, where 12 MOSFETs are equally aligned on a circle shaped circuit board and two circuit boards are stacked in series. An 18 kV-318 A-1 us pulse with a rise time of 289 ns in the short pulse switching test were successfully demonstrated. Moreover, switching tests of 2nd generation MOSFET that has a twice larger device area was conducted. As a result, 60 % reduction of on-resistance was confirmed.