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71.
M. Kobayashi M. Mukai H. Takahashi N. Ohno T. Kawakami T. Ishikawa 《International journal for numerical methods in engineering》2003,58(10):1523-1543
This paper describes the implicit integration and consistent tangent modulus of an inelastic constitutive model with transient and steady strain rates, both of which are time‐ and temperature‐dependent; the transient rate is influenced by the evolution of back stress decomposed into parts, while the steady rate depends only on applied stress and temperature. Such a non‐unified model is useful for high‐temperature structural analysis and is practical owing to the ease in determining material constants. The implicit integration is shown to result in two scalar‐valued coupled equations, and the consistent tangent modulus is derived in a quite versatile form by introducing a set of fourth‐rank constitutive parameters into the discretized evolution rule of back stress. The constitutive model is, then, implemented in a finite element program and applied to a lead‐free solder joint analysis. It is demonstrated that the implicit integration is very accurate if the multilinear kinematic hardening model of Ohno and Wang is employed, and that the consistent tangent modulus certainly affords quadratic convergence to the Newton–Raphson iteration in solving nodal force equilibrium equations. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
72.
系统测量了不同颗粒尺度纳米 SnO_2固体的内耗和模量,发现60℃附近存在一个内耗峰,对应的模量出现异常.烧结温度升高,峰高变化不明显,模量异常减弱.当烧结温度高于400℃时,模量曲线在-15℃附近出现异常,这种模量异常随烧结温度升高而加强,对应的内耗曲线出现一小峰.初步认为,60℃附近内耗峰和模量异常与纳米固体中的结构再有序有关,而-15℃处的模量异常为结构相变引起. 相似文献
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75.
A general variance predictor for Cavalieri slices 总被引:1,自引:0,他引:1
L. M. CRUZ-ORIVE 《Journal of microscopy》2006,222(3):158-165
A general variance predictor is presented for a Cavalieri design with slices of an arbitrary thickness t ≥ 0. So far, prediction formulae have been available either for measurement functions with smoothness constant q = 0, 1, … , and t ≥ 0, or for fractional q ∈ [0, 1] with t = 0. Because the possibility of using a fractional q adds flexibility to the variance prediction, we have extended the latter for any q ∈ [0, 1] and t ≥ 0. Empirical checks with previously published human brain data suggest an improved performance of the new prediction formula with respect to the hitherto available ones. 相似文献
76.
随着时间的推移,混凝土的导温系数将发生变化,为了了解参数随时间的变化规律,利用原型观测资料对导温系数进行分段反演,从而拟合出大坝混凝土导温系数随时间的变化规律. 相似文献
77.
Sarrazin Jean-Christophe; Giraudo Marie-Dominique; Pailhous Jean; Bootsma Reinoud J. 《Canadian Metallurgical Quarterly》2004,30(3):411
In 3 experiments, the authors studied the organization of spatiotemporal information in memory. Stimuli consisted of configurations of dots, presented sequentially. The stimuli were either proportional, with interdot distances corresponding to interdot durations, or not proportional, with interdol distances not corresponding to interdot durations. After a learning phase, participants reproduced the spatial (Experiment 1), temporal (Experiment 2), or spatial and temporal (Experiment 3) characteristics of the target 60 times in succession. In the nonproportional conditions, effects of variable interdot durations or distances on the reproduction of, respectively, constant distances (tau effect) or durations (kappa effect) were observed, whereas no such effects were observed when variable distances or durations were to be produced. Tau and kappa effects influenced the accuracy but not the variability of responses. The results are discussed in light of the distinction between properties of the stabilized mental image and the process of stabilization. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
78.
Jiang-Li Chen Zhuo Xu Shao-Bo Qu Xiao-Yong Wei Xiao-Hui Liu 《Ceramics International》2008,34(4):803-807
The NiFe2O4 and Pb(Zr0.52Ti0.48)O3 ceramic composites are prepared by conventional solid state reaction method. The microstructural and morphological properties of the composites are studied by X-ray diffraction analysis and scanning electron microscopy. Results indicate that the ferrite and piezoelectric phases can co-exist in the composites. The relationship between the dielectric constant and frequency (40 Hz–40 MHz) as well as temperature is also investigated. It is noted that the transition temperature of the composites is about 380 °C. A double electric hysteresis loop is observed in our composites. The magnetic properties are relatively weak according to the magnetic hysteresis loop. With increase in the content of the ferrite phase, the permeability increases. The electromagnetic properties of the as-prepared composites are tunable according to the content of the NiFe2O4 phase. 相似文献
79.
X.B. Tu B. Jian S.J. Wang H.Y. Bian J. Wang S.G. Li 《Tunnelling and Underground Space Technology incorporating Trenchless Technology Research》2005,20(4):1106
Granite is commonly recognized as an ideal medium for underground construction. However, in the site investigation for Heimifeng Pumped Storage Power Station project, it was found that there are swelling behaviors induced by alteration in granite and eventually causing slaking and disintegration of rock blocks. The study shows that hydrothermal alteration in granite is primarily due to the intrusion of multi-phase igneous magma. The clay minerals, such as montmorillonite, chlorite, kaolinite, are the main causes for the swelling behavior of granite. In the exploratory adits, alteration was observed to occur mainly along faults or fractures in the rock masses and resulted in roof caving if water is present. Some of the highly altered borehole cores swell and crack within 24 h in water and eventually disintegrate completely. From the testing results on the samples, the maximum axial free swelling strain is about 1.2%, while the maximum axial confined swelling strain is around 0.1% with swelling stress less than 25 kPa. Under free swelling tests, 80% of swelling is completed within 24 hours. Under confined swelling condition, swelling process is completed within 1 h for some samples, with 80% of maximum swelling strain finished within around 22 h for most of the samples. Contraction of samples occurs after swelling completed. The strength of granite, reflected by deformation and elastic moduli, shear strength, decreases due to alteration. The deformation and elastic moduli are even lower compared to highly weathered rock. The shear strength is between that for highly weathered and slightly weathered rocks. The swelling characteristics of the altered rock present great challenges for support or lining during construction and operation stages. Support or lining shall be in place immediately after excavation. Since the rock may swell when encountering water, the shotcrete shall be designed accordingly. During the construction of access tunnel and caverns, water shall be drained in time. Drainage directly from surface shall be avoided so as to prevent floor heave. 相似文献
80.