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81.
This paper deals with the free vibration analysis of circular alumina (Al2O3) nanobeams in the presence of surface and thermal effects resting on a Pasternak foun- dation. The system of motion equations is derived using Hamilton's principle under the assumptions of the classical Timoshenko beam theory. The effects of the transverse shear deformation and rotary inertia are also considered within the framework of the mentioned theory. The separation of variables approach is employed to discretize the governing equa- tions which are then solved by an analytical method to obtain the natural frequencies of the alumina nanobeams. The results show that the surface effects lead to an increase in the natural frequency of nanobeams as compared with the classical Timoshenko beam model. In addition, for nanobeams with large diameters, the surface effects may increase the natural frequencies by increasing the thermal effects. Moreover, with regard to the Pasternak elastic foundation, the natural frequencies are increased slightly. The results of the present model are compared with the literature, showing that the present model can capture correctly the surface effects in thermal vibration of nanobeams. 相似文献
82.
基坑内撑式支护具有经济、快捷和效率高等特点. 通过郑州市某雨水管道工程基坑支护的实践,介绍了内撑式支护结构在深基坑支护中的受力特点,结构分析与方案选择,为内撑式支护设计和施工提供了参考. 相似文献
83.
84.
85.
D.G. Morris I. Gutierrez-Urrutia M.A. Muoz-Morris 《International Journal of Plasticity》2008,24(7):1205-1223
The creep behaviour of an FeAl intermetallic strengthened by nanosized oxide particles has been examined at temperatures of 700–825 °C. For all temperatures the strain rate shows a power law dependence on the applied stress. At the lowest temperature and with the highest stresses there is evidence of a threshold stress produced by the difficulty of overcoming the particle barriers, while for higher temperatures as well as at low stresses there is no threshold stress and creep appears to be controlled by general climb. The fine oxide particles produce good strengthening at low temperatures but are more readily overcome at high temperatures due to their very small size and limited attractive relaxation force. Despite such fall in creep strength, this material remains one of the strongest iron aluminides to the temperature range evaluated. 相似文献
86.
G. B. Muravskii 《Archive of Applied Mechanics (Ingenieur Archiv)》2008,78(2):149-162
In the paper, a method of averaging displacements in a circular area lying in a linearly elastic transversally isotropic foundation
is developed for the four modes of motion: vertical, horizontal, rocking and torsional. The corresponding formulae are constructed
in a general form which does not depend on the kind of Green functions. For vertical and horizontal modes, uniform load distribution
are applied and the simple integral mean is considered, whereas for rotational modes the load proportional to the distance
from an axis of rotation is used, and angles of rotation for individual points are averaged with weight of the distance squared.
Along with the case of equal radii of circles of loading and averaging, the case of different radii is studied, which allows
one to consider contact problems for embedded axisymmetric foundations having the radius varying with depth. As examples the
following contact problems are studied: static stiffness for a cone embedded in a homogeneous isotropic half-space in vertical
motion, and dynamic stiffness for a disk on a layer resting on a homogeneous half-space for four modes of motion. Comparisons
with the corresponding exact solutions are carried out. 相似文献
87.
88.
P. Z. Lugovoi V. F. Meish B. P. Rybakin G. V. Secrieru 《International Applied Mechanics》2008,44(7):788-793
A numerical algorithm to determine the stress-strain state of a reinforced cylindrical shell subject to impulsive loading
is elaborated. Results from a numerical analysis of the dynamic behavior of a reinforced elastoplastic shell under explosive
loading are presented
__________
Translated from Prikladnaya Mekhanika, Vol. 44, No. 7, pp. 83–90, July 2008. 相似文献
89.
90.
近断层地震作用下钢筋混凝土连续梁桥地震易损性分析 总被引:1,自引:0,他引:1
考虑桥墩、支座构件及主梁的碰撞损伤指标,对钢筋混凝土连续梁桥进行了地震易损性分析.综合考虑了结构参数的不确定性,从太平洋地震工程研究(Pacific earthquake engineering research,PEER)数据库中随机选取了20条近场地震记录,得到大量的随机地震-结构样本.结合不同破坏状态下的桥梁损伤指标,根据结构的能力与需求得到了桥梁各构件及整体桥梁结构的地震易损性曲线.从概率意义上判断在强烈地震作用下桥梁结构所处的破坏状态,为今后在役的同类型桥梁震害预测提供了参考. 相似文献