Papers by Keyword: Temperature Effects

Abstract: The reverse-bias current-voltage characteristics of commercial 1200 V 4H-silicon-carbide junction barrier Schottky (SiC-JBS) rectifiers are studied both experimentally and through numerical simulation. The reverse leakage current measured from physical devices is observed to display both a strong temperature and field dependence. A model is presented to explain the observed behavior based on a combination of trap-assisted tunneling and a thermionic-emission mechanism through a potential barrier located at the metal-SiC interface. The study shows that a two-level trapping model can be necessary to properly explain the measured data. Excellent agreement between the models and the measurements is obtained over a wide range of bias and temperature.

Abstract: Two different methods for reducing the operating temperatures of non-concentrating photovoltaic panels are analyzed and the performances are compared. Forced air cooling using a low power fan and use of a thermo siphon heat pipe are the modifications proposed for the purpose of efficiency enhancement. Experimental results of the two techniques are compared. It was found that, using a specific flow rate and selection of the proper heat pipe fluid and its operating conditions could help to reduce panel temperature considerably.

Abstract: The distribution of the temperature gradient and temperature change of the pre-stressed concrete box girder are extremely complicated because of the multiplex environment. Temperature load has attached great importance in the field of engineering, and it has a great influence on the bridge’s structure, especially the box structure. The engineering background of this paper is a typical three-dimensional pre-stressed concrete continuous box girder bridge with variable cross section, comprising five spans in one continuous unit. Experiment on it and research the change rules of the temperature distribution, as well as the influence of the structure’s internal force resulted by temperature. Finite element software-Midas/FEA is used to model and calculate the bridge in order to analyze the temperature influence on structure’s stress in contrast to the measured data from the experiments

Abstract: In 2003, people working in the San Luzi, Zuoz, bell tower reported excessive tower vibrations when ringing bells. Zuoz is a village in the Upper Engadin Valley, Switzerland. Measurements performed in 2004 showed a maximum tower vibration velocity amplitude of 16 mm/s which is more than five times the acceptable value ([1], [2], [3]). In 2008 the two large bells (out of four) were equipped with cranked yokes and their pendulum frequency was reduced to get a larger distance to the tower natural frequency. Measuring again in 2009 yielded the two large bells no longer exciting large tower vibrations. However, this was not true for bell No. 3. Subsequently, this bell's pendulum frequency was also reduced. In 2011, measurements showed that this last measure had negative instead of positive effects. And, now disposing of three values, the tower natural fundamental frequency was found to be somewhere in the f = 1.43...1.50 Hz region. It was then decided to monitor the tower dynamic behavior for one year to get reliable information on the natural frequency scatter. Monitoring started June 11, 2012, and ended October 7, 2013. The results: a) The tower fundamental frequency varied in an f = 1.42...1.59 Hz range, b) The tower is stiffer in winter than in summer, c) On a daily or weekly schedule, the tower fundamental frequency is following the temperature curve: increasing stiffness with increasing temperature and vice versa. A possible explanation for this contradiction is given. Due to space restrictions, also monitored bell ringing excited tower vibrations can not be discussed here.

Abstract: Three examples involving size effects are presented with implications concerning the formability: small Ni-20wt.%Cr resistive bridges, magnetic micro-sensors performed with (Ni, Co, Fe) based alloys and copper clad aluminum thin wires. The mechanical properties are directly linked to the ratio thickness over grain size (t/d ratio) of the parts. These metallurgical considerations must be taken into account when we are concerned by the numerical simulation of the process of such components. It is shown that the simulations can correctly reproduce the softening effect linked to a decrease in thickness and in number of grains across the thickness: the quality of the final shape strongly depends on the number of grains across the thickness. Finally the effect of a moderate increase in temperature on these results will be briefly reported.

Abstract: The spectral characteristic of the fluorescence film used in dissolved oxygen sensor is influenced by temperature. In this paper, we quantitatively studied the temperature effect of the dissolved oxygen sensitive film based on Ru (bpy)₃²⁺ complexes. In order to study how it was affected, two experiments were designed. One experiment was carried out when the sensitive membrane was dipped into solution of saturated sodium sulfite, in which case, there was no oxygen interference. The other experiment was implemented when the sensitive film was exposed to air, while the influence of oxygen was constant. In the processes of both experiments, we adjusted the temperature around the sensitive membrane. When the temperature rising from 0°C to 45°C, the fluorescence intensity emitted from the sensitive film was reduced which in the first experiment decreased from 5030counts to 3845counts and in the second experiment from 2314counts to 1407counts. Then a method can correct the temperature effect was proposed. The curve of spectrum at 25°C was supposed to be the standard and spectrums at other temperatures was corrected to be consistent with it. The correction coefficient of every wavelength was got through our calculation. After multiplying the coefficients, fluorescence intensity at different temperatures was approximately equal and the differences caused by temperature were eliminated.

Abstract: With the increasing demand for high efficiency, low cost and the bulk, so the production of micro-forming has a very important significance. Firstly, the introduction of micro-forming is introduced in this paper. Then, its basic theory, including size effects and temperature effects, is presented. At last, a future research direction is highlighted.

Abstract: Lamb waves are the most widely used guided ultrasonic waves for structural damage detection. One of the major problems associate with Lamb wave propagation is the effect of temperature on wave propagation parameters. It is important that these parameters are more sensitive to damage than to varying temperature. The paper demonstrates how amplitude and arrival time of Lamb waves are affected by temperature. The analysis is performed for the experimental data gathered from Lamb wave propagation in a damaged aluminium plate. A simple clustering algorithm is used to distinguish between "undamaged" and "damaged" conditions in the presence of changing temperature.

Abstract: A series of laboratory tests was carried out to assess the time-dependent creep behaviour of EPS geofoam at room temperature (23°C) and at 40°C. The experimental data were then used to calibrate and to validate mechanical viscoelastic models along with an empirical Power Law model, at these two temperatures. The viscoelastic models examined were the 3-element (Maxwell-Kelvin), the 4-element (Burgers) and the Modified 4-element models. The modified 4-element model and the base case, the empirical power law model, were found to give the best predictions. As anticipated, the experimental results show that creep rate is higher at elevated temperatures. The results, at 23°C and 40°C, offer a means to assess and model creep behavior in geotechnical applications at normal, and at a practical elevated, temperature where use of EPS geofoam in warmer climate may be a concern.

Abstract: Titanium alloys, such as Ti-6Al-4V, offer favorable characteristics as significant strength, biocompatibility and metallurgical stability at elevated temperatures. These advantages afford the application of parts out of Ti-6Al-4V in a wide field within aerospace, astronautic and medical technologies. Most applied shaping operations for parts out of titanium alloys are forging, casting, forming and machining. In order to develop and improve forming operations numerical simulations are applied during preprocessing. For that purpose mechanical properties of the material such as yield stress and Lankford parameter have to be determined. Due to the two-phase (α + β) microstructure of Ti-6Al-4V, forming operations have to be carried out at elevated temperatures to reduce the required forming force and extend forming limits. Taking the temperature and stress state dependency of the material into consideration, uniaxial tensile and compression tests are accomplished at elevated temperatures, ranging from 400 to 600 °C. Furthermore, the experimentally determined yield stress and Lankford parameter are approximated with the yield loci model proposed by Barlat 2000. The model predicts the flow response of the material, thus provides input data for the finite element analysis of forming processes at different temperature levels.