共查询到20条相似文献,搜索用时 93 毫秒
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为了研究粘性效应作用下的动态扩展裂纹尖端渐近场,建立了蠕变材料Ⅱ型动态扩展裂纹的力学模型,在稳态蠕变阶段,弹性变形和粘性变形同时在裂纹尖端场中占主导地位,应力和应变具有相同的奇异量级,即(σ,ε)∝r-1/(n-1)。通过渐近分析求得了裂纹尖端应力、应变和位移分离变量形式的渐近解,并采用打靶法求得了裂纹尖端应力、应变的数值结果,数值计算表明,裂尖场主要受材料的蠕变指数n和马赫数M的控制。通过对裂纹尖端场的渐近分析,从应变角度出发,提出了蠕变材料Ⅱ型动态扩展裂纹的断裂判据。 相似文献
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SiC/Al梯度功能材料各梯度层由不同体积浓度的陶瓷和金属组成,由于材料组分梯度变化,克服了双材料界面的应力突变问题,获得了优异的使用性能.本文首先采用激光云纹干涉法,对具有四个梯度层的SiC/Al梯度功能材料紧凑拉伸试件在机械荷载作用下的拉伸实验位移场进行记录,进而获得紧凑拉伸试件裂纹口位移P-V曲线以及材料断裂韧度实验值;然后根据层合梯度功能材料理论分析模型,建立FGM紧凑拉伸试件的渐近分网有限元平面应变模型,采用通用有限元软件的单元删除模块对试件模型进行裂纹扩展单元的应变模拟分析,从计算所得的裂纹尖端应变图像分析得出梯度材料试件的裂纹扩展规律. 相似文献
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为了研究粘性效应作用下的动态扩展裂纹尖端渐近场,建立了可压缩粘弹性材料II型动态扩展裂纹的力学模型,推导了可压缩材料Ⅱ型动态扩展裂纹的本构方程.在稳态蠕变阶段,弹性变形和粘性变形同时在裂纹尖端场中占主导地位,应力和应变具有相同的奇异量级r-1/(n-1).通过渐近分析求得了裂纹尖端应力、应变和位移分离变量形式的渐近解,并采用打靶法求得了裂纹尖端应力、应变和位移的数值结果,给出了应力、应变和位移随各种参数的变化曲线.数值计算表明,弹性变形部分的可压缩性对Ⅱ型裂尖应力场影响甚微,而对应变场和位移场影响较大.裂尖场主要受材料的蠕变指数n和马赫数M的控制.当泊松比ν =0.5时,可以退化为不可压缩粘弹性材料Ⅱ型动态扩展裂纹. 相似文献
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本文对NiTi形状记忆合金I型裂纹尖端热力耦合行为进行了数值仿真分析和实验验证。建立了包含相变和热力耦合的本构模型,通过有限元计算得到了裂纹尖端附近的纵向应变、马氏体体积分数和温度场分布,依据马氏体相变情况对裂纹尖端有效应力强度因子进行了修正,揭示了加载速率对形状记忆合金裂纹尖端有效应力强度影子的影响规律。参数研究表明,随着加载频率的增加,裂纹尖端附近温度逐渐升高,马氏体相变区域逐渐缩小,有效应力强度因子呈下降趋势,形状记忆合金表现出增韧效应,有助于减缓裂纹扩展。本研究结果对于揭示热力耦合作用下超弹性形状记忆合金疲劳裂纹扩展规律具有重要参考意义。 相似文献
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一种非局部弹塑性连续体模型与裂纹尖端附近的应力分布 总被引:7,自引:0,他引:7
本文提出一种非局部弹塑性连续体模型。在这个模型中,应力与弹性应变之间为非局部线性关系,而塑性应变与总应变历史相联系。对于形变理论,假定塑性应变张量与总应变偏量张量成比例,其比例因子是总有效应变的标量函数。将这一模型用于分析幂硬化弹塑性材料拉伸型裂纹尖端附近的应力场,利用经典断裂力学中所得的拉伸型裂纹尖端HRR奇性解的结果,在一维简化计算下导出了裂纹正前方的拉应力分布和最大拉应力的表达式,证明临界J积分准则可由非局部最大拉应力准则得到。用已有的实验数据计算了几种钢材在裂纹起始扩展时裂纹尖端附近的最大拉应力,发现其量级与晶格内聚强度相近。所得结果对于理解材料断裂过程的物理机理是有益的。 相似文献
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V. S. Nagornyi 《Journal of Applied Mechanics and Technical Physics》2000,41(2):225-230
The physical and mathematical principles of the method of electrogas-and electrohydrodynamic conversion of electrical signals
to pneumatic (hydraulic) signals and vice versa for control of gas and liquid jets and flows in electropneumohydraulic systems
are considered.
St. Petersburg State Technical University, St. Petersburg 195251. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika,
Vol. 41, No. 2, pp. 25–31, March–April, 2000. 相似文献
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Richard E. Whaley 《Experimental Mechanics》1962,2(11):329-334
This paper describes a method of presentation of fatigue data on three commonly used aircraft materials, 2024-T3 and 7075-T6 aluminum alloys and normalized SAE 4130 steel, such that variations in fatigue strength with stress-concentration factor can be shown. Comparisons of the fatigue strengths of 2024-T3 and 7075-T6 aluminum are made for the most useful range of stress-concentration factors. Static-strength results of notched and unnotched specimens of the three materials are presented to show how the strength varies with some parameters of the stress concentration. Comparison of the data with one theory for the strength of cracked specimens was made. 相似文献
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STICTION AND ANTI—STICTION IN MEMS AND NEMS 总被引:6,自引:1,他引:6
赵亚溥 《Acta Mechanica Sinica》2003,19(1):1-10
Stiction in microelectromechanical systems (MEMS) has been a major failure mode ever since the advent of surface micromachining
in the 80s of the last century due to large surfacearea-to-volume ratio. Even now when solutions to this problem are emerging,
such as self-assembled monolayer (SAM) and other measures, stiction remains one of the most catastrophic failure modes in
MEMS. A review is presented in this paper on stiction and anti-stiction in MEMS and nanoelectromechanical systems (NEMS).
First, some new experimental observations of stiction in radio frequency (RF) MEMS switch and micromachined accelerometers
are presented. Second, some criteria for stiction of microstructures in MEMS and NEMS due to surface forces (such as capillary,
electrostatic, van der Waals, Casimir forces, etc.) are reviewed. The influence of surface roughness and environmental conditions
(relative humidity and temperature) on stiction are also discussed. As hydrophobic films, the self-assembled monolayers (SAMs)
turn out able to prevent release-related stiction effectively. The anti-stiction of SAMs in MEMS is reviewed in the last part.
The project supported by the Distinguished Young Scholar Fund of NSFC (10225209), key project from the Chinese Academy of
Sciences (KJCX2-SW-L2) and National “973” Project (G1999033103) 相似文献
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本文针对现代换热设备设计、两相流动与传热研究的需要,介绍了可供科研使用的水和水蒸汽物性计算方法,完善了计算程序。根据超临界锅炉设计中的超临界水的物性计算,两相流研究和换热设备动态特性研究中对物性导数计算的需要,提供了两个算例,并进行了定性分析。 相似文献
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Amit Acharya 《Journal of Elasticity》2011,104(1-2):23-44
A methodology is devised to utilize the statistical mechanical entropy of an isolated, constrained atomistic system to define constitutive response functions for the dissipative driving-force and energetic fields in continuum thermomechanics. A thermodynamic model of dislocation mechanics is discussed as an example. Primary outcomes are constitutive relations for the back-stress tensor and the Cauchy stress tensor in terms of the elastic distortion, mass density, polar dislocation density, and the scalar statistical density. 相似文献
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Jean-François Pinton Guillaume Brillant 《Theoretical and Computational Fluid Dynamics》2005,18(6):413-433
We review several aspects of the propagation of sound in vortical flows. We restrict ourselves to isothermal, humidity-free flows at low Mach number M. Since vorticity plays a major role in vortex-flow interactions we focus on vortical flows. We consider two main canonical situations. The first concerns the transmission of sound. We analyze the evolution of acoustic wavefronts as they propagate across a single vortex. The second situation addresses the scattering of sound waves by nonstationary vortices. We study the evolution of the acoustic pressure emitted in the far field, at an angle with the initial direction of propagation. In this geometry one performs direct spectroscopy of the flow vorticity field. In each case, we review theoretical results and compare with experimental measurements and numerical simulations when available. We also briefly report how the following new acoustic techniques have recently been used to study complex or turbulent flows: time-resolved acoustic spectroscopy, speckle interferometry and Lagrangian particle tracking. PACS 43.25, 43.28, 47.32, 67.40 相似文献
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Francisco J. Montáns Francisco Chinesta Rafael Gómez-Bombarelli J. Nathan Kutz 《Comptes Rendus Mecanique》2019,347(11):845-855
In the past, data in which science and engineering is based, was scarce and frequently obtained by experiments proposed to verify a given hypothesis. Each experiment was able to yield only very limited data. Today, data is abundant and abundantly collected in each single experiment at a very small cost. Data-driven modeling and scientific discovery is a change of paradigm on how many problems, both in science and engineering, are addressed. Some scientific fields have been using artificial intelligence for some time due to the inherent difficulty in obtaining laws and equations to describe some phenomena. However, today data-driven approaches are also flooding fields like mechanics and materials science, where the traditional approach seemed to be highly satisfactory. In this paper we review the application of data-driven modeling and model learning procedures to different fields in science and engineering. 相似文献