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871.
A large scale model analysis, using embedded strain gauges, of the strain distribution in the cement mantle surrounding a femoral prosthesis is underway. In order to predict, and so avoid, positions of locally high strain gradients in this model, a finite element and experimental analysis of a similar problem was undertaken. For this purpose, a loose fitting rectangular steel insert inside a surrounding rectangular epoxy sheath was used to model an extreme case of the torsional and bending components of hip joint load. The axial component of joint load was modelled using an axisymmetric finite element model of a tapered shaft. The finite element results were used to determine suitable positions for embedding gauges in the experimental model. Results showed that the finite element analysis failed to adequately model the close sliding fit between the steel insert and epoxy. Altering the experimental model to artificially replicate the finite element contact conditions produced good correlation in bending, with experimental strains agreeing with simple bending theory to within 6%. Satisfactory correlation under torsional loading was not obtained, but strain magnitudes were low. Predicted positions for embedding gauges give conservative results, lessening the possibility of strain gradient induced error in the large scale model test of the cement mantle and prosthesis. 相似文献
872.
A high sensitivity thermoelectric sensor to measure all relevant thermal transport properties has been developed. This so-called transient hot bridge (THB) decidedly improves the state of the art for transient measurements of the thermal conductivity, thermal diffusivity, and volumetric specific heat. The new sensor is realized as a printed circuit foil of nickel between two polyimide sheets. Its layout consists of four identical strips arranged in parallel and connected for an equal-ratio Wheatstone bridge. At uniform temperature, the bridge is inherently balanced, i.e., no nulling is required prior to a run. An electric current makes the unequally spaced strips establish an inhomogeneous temperature profile that turns the bridge into an unbalanced condition. From then on, the THB produces an offset-free output signal of high sensitivity as a measure of the properties mentioned of the surrounding specimen. The signal is virtually free of thermal emf’s because no external bridge resistors are needed. Each single strip is meander-shaped to give it a higher resistivity and, additionally, segmented into a long and short part to compensate for the end effect. The THB closely meets the specific requirements of industry and research institutes for an easy to handle and accurate low cost sensor. As the key component of an instrument, it allows rapid thermal-conductivity measurements on solid and fluid specimens from 0.02 to 100 W· m−1·K−1 at temperatures up to 250°C. Measurements on some reference materials and thermal insulations are presented. These verify the preliminary estimated uncertainty of 2% in thermal conductivity. 相似文献
873.
S. Krishnankutty R. M. Kolbas M. A. Khan J. N. Kuznia J. M. Van Hove D. T. Olson 《Journal of Electronic Materials》1992,21(6):609-612
The low temperature (77 K) photoluminescence characteristics of Al
x
Ga1-x
N-GaN strained layer quantum wells with differentx values grown by metalorganic chemical vapor deposition (MOCVD) were investigated. The photoluminescence spectra were useful
in analyzing both quantum confinement effects and strain induced energy shifts. The strain induced shifts were found to be
a strong function of aluminum compositionx. A model was developed to calculate the strain induced bandgap shifts atk = 0. The values predicted by this model which took into account the wurtzite crystal structure of the material system, were
in good agreement with (i.e. within 2 meV of) the experimentally measured shifts. 相似文献
874.
The evaluation of the bending strain tolerance and AC loss properties for monoand multi-filamentary Bi-2223 Ag-sheathed tape
were carried out at liquid nitrogen temperature. For tapes with a filament number of over 19, the critical current (Ic) was maintained at the same values up to the bending strain of 0.3%, although the Ic of the mono-filamentary tape at the condition of 0.2% strain degraded to 90% of the value for the no-strain condition. The
AC loss of the monofilamentary tape was the hysteresis type. On the contrary, the AC loss of the multi-filamentary tape was
substantially dominated by the eddy current loss in the Ag matrix. 相似文献
875.
A. N. Iyer S. Salib M. Mironova C. Vipulanandan U. Balachandran K. Salama 《Journal of Superconductivity》1998,11(5):533-543
The powder-in-tube technique consisting of industrial processes such as wire drawing and rolling has been widely used to fabricate superconducting tapes. In the present investigation a novel technique was adopted to fabricate BSCCO 2223 tapes. Instead of wire drawing, the silver billet was reduced in size by groove rolling. Stress conditions during groove rolling were analyzed and appropriate changes were incorporated to optimize the deformation process. Subsequent thermomechanical treatment resulted in tapes with average critical current densities of 18,000 A/cm2. Phase development and microstructural evolution during the thermomechanical treatment were studied using XRD, SEM, and TEM. The electromechanical properties of monofilament and composite BSCCO tapes were evaluated by subjecting them to in situ tensile tests. The strain tolerance of the composite was found to be better than that of the monofilament BSCCO tape. 相似文献
876.
Dynamic strain aging has been investigated at temperatures between 77 and 1100 K in eight polycrystalline NiAl alloys. The 0.2% offset yield stress and work hardening rates for these alloys generally decreased with increasing temperature. However, local plateaus or maxima were observed in conventional purity and carbon doped alloys at intermediate temperatures (600–900 K). This anomalous behavior was not observed in low interstitial high-purity, nitrogen doped, or in titanium doped materials. Low or negative strain rate sensitivities (SRS) were also observed in all eight alloys in this intermediate temperature range. Coincident with the occurrence of negative SRS was the occurrence of serrated flow in conventional purity alloys containing high concentrations of Si in addition to C. These phenomena have been attributed to dynamic strain aging (DSA). Chemical analysis of the alloys used in this study suggests that the main species causing strain aging in polycrystalline NiAl is C but indicate that residual Si impurities can enhance the strain aging effect. 相似文献
877.
878.
水下压力测量传压管道动态特性分析 总被引:1,自引:0,他引:1
介绍了用于水下发射膛压测量的压力传感器,针对水下测压时有无充脂所出现的不同现象,以理论推导分析了产生此现象的原因。得出结论:在水下发射装置测压,必须对传感器传压管道进行充脂,以排空管道内的空气,保证传压管的固有频率满足测试要求。 相似文献
879.
The aim of this study was to compare the physiological and subjective strain in workers wearing a disposable “Tyvek” (TYV) and a ventilated “Mururoa” (MUR) coverall in a real working situation. Eleven men performing normal abatement tasks volunteered to participate. Physiological measurements included oral temperature, heart rate and sweat loss. Subjective evaluations of clothing comfort, cooling, robustness, cumbersomness, acceptable exposure duration and physical exertion were carried out at the end of the task. The ventilated MUR reduced heat strain. Indeed, it allowed significantly higher sweat loss than TYV and showed a tendency to reduce the increase in oral temperature. Subjective ratings reveal that MUR was considered better than TYV in terms of clothing comfort, coolness and robustness. On the other hand, MUR is more cumbersome to wear. In this study, where workload and heat stress were moderate, there were few differences between the two coveralls in terms of physiological strains, but far more significant differences in the subjective ratings. 相似文献
880.
Romanov S. V. Stepanov G. V. Kharchenko V. V. Babutskii A. I. Lankin Yu. N. Feofentov N. A. Kravchenko I. V. 《Strength of Materials》2003,35(4):430-433
he paper describes a 32-channel system for studying full-scale structures developed with the use of the state-of-the-art components. It provides continuous long-term measurement of strains and temperatures up to + 350°C and accumulation and storage of measurement data. The system was used to record the elastic strains and temperatures of a welded joint of the hot collector to the PGV-1000 steam generator nozzle in the period between the preventive maintenances. The measurement results reveal a complex pattern of strain and temperature distribution different from the axisymmetric one. 相似文献