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71.
The strength of case-hardened parts under cyclic loading can be determined in an experimental manner, but this can produce
a large amount of costs due to the expenditure of material and testing time. Therefore, a calculation method is developed,
that strongly reduces the number of experiments. The presented model is based on Weibull's weakest-link concept and allows
to compute the survival probability of a case-hardened part which is loaded close to the fatigue limit. The essential quantities
in this model are the distribution of Vicker's hardness of the material, the exponents of the Weibull distribution of the
volume and the surface, the residual stress state, the surface roughness and the surface oxidation depth. By integrating the
survival probabilities of the surface and the volume, the survival probability of the entire specimen or part can be calculated,
which allows to compute the fatigue limit. The necessary parameters have to be determined from reference specimens. The model
is successfully examined by comparing experimental and calculated results of smooth and notched case-hardened specimens under
alternating torsion, rotating bending, repeated tension and tension-compression.
Received 20 August 2001 / Accepted 11 November 2001 相似文献
72.
73.
Prediction of cracking within early-age concrete due to thermal, drying and creep behavior 总被引:2,自引:0,他引:2
To predict potential early-age cracking after concrete placing, a numerical simulation procedure has been completed based on a micromechanical model and empirical formulas on the property development of young concrete. The numerical model could account for the effects of hydration, moisture transport and creep. Environmental influences, such as removal of formworks, curing conditions and variations of surrounding temperature and relative humidity, have been investigated. In calculating stress field with age caused by these synthetic physical-mechanical processes, three-dimensional finite element and finite difference (3D-FE-FD) methods are combined together. 相似文献
74.
《Drying Technology》2007,25(1):75-84
This article proposes a multiscale computational model able to calculate energy consumption in a batch lumber kiln. A dual-scale computational model of wood drying deals with the boards/stack interaction and serves as a basis for the present work. A new module was added here that calculates heat losses through kiln walls (convection, condensation) and the energy used by each kiln component (fans, heating elements, humidifier, vacuum pump, etc.). The corresponding mathematical formulation is presented and then theoretical results are compared to those collected in an industrial vacuum kiln. As application example, the effect of air reversal, air velocity, and kiln insulation are exhibited, which depicts the great potential and prospects of this new tool for energy savings in relation to the product quality. 相似文献
75.
76.
77.
数值地形图的生成及其水文地貌特征评价 总被引:17,自引:2,他引:15
数值地形图(DEM)是利用地理信息系统(GIS)进行流域水文模拟的基础, 其精度直接影响模拟结果在没有现成的数值地形图时, 应用人员往往利用传统的地形图来生成它. 本文分别采用Arc/Info地理信息系统软件提供的哈奇逊法和不规则三角网五次插值法, 对一个实验流域的高程取样点进行插值, 生成了4种不同的数值地形图, 从凹洼分布、流域界定、河网提取、地面坡度和地形指数、以及地面径流汇成等方面, 对它们的水文地貌精度进行了比较. 结果表明, 两种方法都能生成由高程点群所反映的地形, 然而由于哈奇逊法能够结合流域的河网结构及其具有物理基础的水文地貌加强法来处理凹洼问题, 因此大大地提高了其所生成的流域数值地形图水文地貌特征精度. 相似文献
78.
We modeled nisin's anticlostridial activity and assessed the antagonistic or potentiating influences of food ingredients. The model systems contained yeast extract, proteose peptone, and glucose; were supplemented with protein (0.075, 0.75, 7.5% w/v), phospholipid (0.075, 0.75, 7.5% w/v), or soluble starch (5, 17.5, 30% w/v); and were adjusted to pH 5.5, 6.0, or 6.5. Samples inoculated with 104/mL spores were incubated at 15, 25, or 35°C. Statistical analysis developed an equation (r2= 0.76) that modeled the response and identified temperature as the most significant (α 0.001) variable. Nisin lost effectiveness with increasing temperature. Nisin concentration had significant positive and phospholipid negative, linear effects. Many interactive effects were significant (α 0.20). Nisin inhibited C. botulinum until its residual level dropped below a threshold, which decreased from 154 IU/mL at 35°C to 12 IU/mL at 15°C. 相似文献
79.
Mathematical models describing dynamics of crust formation and kinetics of crust color and firmness changes were developed for the deep-fat frying of beef meatballs. Good agreement (R2 ranged between 0.815 and 0.987) was observed between experimental and predicted data. Crust color lightness, redness, and yellowness decreased exponentially with frying time while total color change increased. All color parameters followed first order reaction kinetics. Meatball firmness was measured by peak force obtained from a puncture test whose kinetics model had a reaction rate constant of 5.39E-3 1/(s.Nn-1) and a reaction order of 0.0013. 相似文献
80.
蚕庄金矿倾斜采场的地压研究 总被引:1,自引:0,他引:1
本文使用工程地质、室内试验及数值分析的方法对蚕庄金矿的倾斜矿房的地压活动规律进行了研究,得出了一些有价值的结论。 相似文献