Papers by Keyword: Hysteresis

Abstract: There is an ongoing interest in the research and application of thin film coatings containing titanium oxides and titanium nitrides, due to their properties such as photocatalytic activity, mechanical hardness, biocompatibility, and so on. Reactive sputter deposition is widely used for the production of such coatings. A characteristic of this method is the hysteresis, which leads to an ambiguous dependence of the deposition rate and the coating quality on the process conditions. There are a number of theoretical models describing reactive magnetron sputtering. One of the most advanced is the RSD2013 model. Several parameters in this model can only be determined experimentally. This article focuses on the investigation of the hysteresis during the reactive magnetron sputtering deposition process. The RSD2013 parameters that describe the experimental setup were determined, and on their basis the dependences of the characteristics of the hysteresis region on the discharge power, the type of reactive gas, and the working gas pressure were investigated. Additionally, the growth rate of the thin film coating prepared in various modes was compared with the RSD2013 model, which is in agreement with the experimental data. The results obtained from the RSD2013 model in comparison to the experimentally obtained data make it possible to provide an overview of suitable operating modes for the deposition of titanium dioxide and titanium dioxide for the magnetron sputtering device used.

Abstract: SiC MOSFETs have already replace silicon-based device in power applications, even if some technological issues are still not solved. The most important of them is related to the complex traps distribution at SiC/SiO₂ interface. Interface traps affect the overall device behavior, modifying channel mobility and introducing hysteresis. In this work experimental C-V and I-V curves are carried out on various commercial SiC MOSFET at different temperatures. The focus is the comparison of hysteresis arising in trench and planar SiC MOSFETs.

Abstract: Hysteresis is observed in various mechanical systems. For structural elements, cyclic loads cause deterioration of their characteristics due to cracks opening, yielding and buckling of metal­lic elements, etc. This contribution presents a smooth hysteresis model for reinforced concrete (RC) structural elements that accounts for both damage and pinching effects. The model is based on the Bouc­-Wen differential equation. Deterioration of the mechanical properties is introduced through a damage index that includes energy dissipation and ductility. Pinching is simulated by acting directlyon the stiffness of the system. The parameters of the model have clear physical meanings, which helps in the identification and interpretation of the results. Applications to RC elements show that the model is suitable for describing complex cyclic behaviours involving effects of damage. Being defined by a smooth hysteresis law, the model is a computationally-­effective tool useful for dynamic and stochastic simulations.

Abstract: The energy dissipation for one cycle of clay soil deformation over the area of ​​a hysteresis loop under conditions of one-dimensional deformation has been experimentally studied. Several series of trials were carried out under different conditions of soil density and moisture and different loading modes. It was established by the experiments that after several cycles of loading and unloading of the samples, the transient process of the closed loop formation ends and certain dependences of stress on deformations are established in the sections of the ascending and descending branches of the hysteresis loop. To determine these dependencies, rheological relations obtained directly from the hysteresis loop by approximating the arcs of its contour have been used. By integrating the approximating rheological dependences along the branches of the loop, the dissipated energy per deformation cycle has been obtained as a function of cyclic deformation amplitude, measured by the area of the hysteresis loop. Experiments on obtaining a hysteresis loop were carried out on a compression device with a cyclic sample. Samples with different states of density and moisture content were produced by consolidating a paste having yield point moisture under different pressures. Several series of experiments have been carried out. In the first series, soil absorption coefficients were derived for different states of density-moisture at different loading rates. In the second series, three types of clayish soil (clay, loam, sandy loam) were studied. Dissipation coefficients have been found out for the indicated soils. In the third series, three types of clay soil were tested under different conditions of density and moisture. The dissipation coefficients have been obtained. In the fourth series, the dependences of the absorption coefficient on the amplitude value of the cyclic stress for three types of clay soil were disclosed. It was found that a change in the loading rate within the range from 0.05 MPa to 0.2 MPa does not lead to the significant change in the absorption coefficient, the increase in the number of clay fractions in the sample leads to an increase in the absorption coefficient, a change in the amplitude of cyclic loading (in the indicated range of change) does not affect the absorption coefficient.

Abstract: In order to study the effect of temperature changes on the dissipative properties of materials, two approaches are used. The first approach implies introducing some temperature function under the sign of the integral in the heredity theory equation and simultaneously taking into account the dependence of the elastic modulus on temperature. As a result, based on experimental data on the thermal creep of soils, the expression for determining the hysteresis energy losses under the periodic voltage changes was obtained depending on temperature changes.According to the second approach, the expression for determining the hysteresis energy losses under isothermal conditions at different temperatures was obtained by introducing into the heredity theory equation an approximation of the experimental dependences of instantaneous deformation and temperature creep parameters for steel Kh18 N10T.

Abstract: This study involved an experimental investigation of the hydrodynamic lubrication performance of dimpled seal-like thrust bearings. Circular dimples were created on lubricating surfaces and the hydrodynamic effects were evaluated. The load-carrying capacity and frictional torque were measured under a constant film thickness. The lubricating surface was observed to make clear the effect of the cavitation area on the load-carrying capacity and the frictional torque. Dimpled specimen produced the load-carrying capacity and it showed a signature hysteresis phenomenon. Cavitation strongly affected the phenomenon. In addition, the dimpled specimen could reduce the frictional torque compared with the plane (dimple-free) specimen. However, the hysteresis phenomenon of the frictional torque was not clear compared with that of the load-carrying capacity.

Abstract: Fatigue crack growth in NR/BR compound and the effect of two different types of recycled rubber powder (RRP) i.e. micronized cryo-ground 74 μm and ambient-ground 400 μm were studied using fracture mechanics approach. Absolute and relative hysteresis losses using single-edge notch tensile (SENT) specimens were determined with a displacement-controlled strain compensating for permanent set of the samples throughout the Fatigue Crack Growth (FCG) experiments. Results indicated a correlation between absolute/relative hysteresis loss and fatigue crack growth rate under specific dynamic strain amplitudes. Differences in relative hysteresis loss showed that additional energy dissipation, due to multiple new crack surfaces at the crack tip, contributes to the FCG of the RRP compounds. At higher tearing energy, beside other factors affecting the FCG performance of the RRP compounds, both higher absolute and relative hysteresis loss are slightly detrimental to the crack growth rates.

Abstract: Ising core-shell model was proposed to reconstruct superparamagnetism hysteresis in nano-goethite (α-FeOOH). Core and shell set as antiferromagnetic and paramagnetic state respectively. Core and shell radius varies until the theoretical hysteresis fit with experiment hysteresis. At low temperature, the hysteresis reconstructed nicely with 55% antiferromagnetic core contribution and 45% paramagnetic shell contribution. At high temperature, the core-shell model show unrealistic result compared to the pure paramagnetic state.

Abstract: In this paper, we report on the simulation results of instability threshold voltage of SiC MOSFET device. Hysteresis cycles of threshold voltage suggest that trapping and detrapping phenomena of electrons from the SiC layer into the oxide traps occur. Experiment suggests that positive threshold voltage shifts (ΔV_th) caused by a positive stress voltage to the gate, are almost fully recovered by applying negative stress voltage. This work assumes uniform trap densities extending from SiC interface at a limited depth into oxide.

Abstract: In this paper, we consider the technological features of the formation of thin ferroelectric films of lead zirconate titanate (PZT) by the method of plasma high-frequency reactive sputtering. The crystal structure, morphology and elemental composition of films deposited on silicon and oxidized silicon substrates are investigated. It is shown that the obtained PZT films have a perovskite structure and are polycrystalline with a predominant crystallite growth in the (110) direction. An automated test bench has been designed and manufactured for measuring the electrophysical parameters of ferroelectric films. The measured CV characteristics of the Ni/PZT/Si structure show the hysteresis caused by the polarization of the PZT film. It is noted that the asymmetry of the dependence of the spontaneous polarization on the applied voltage can be caused by the presence of surface states at the PZT/Si interface.