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951.
952.
Thierry Woignier George W. Scherer Adil Alaoui 《Journal of Sol-Gel Science and Technology》1994,3(2):141-150
Although supercritical drying avoids the capillary stresses that tend to warp and crack xerogels, there are other sources of stress that interfere with the preparation of monolithic aerogels. In this paper, we present experimental results showing that there is a limit to the rate at which the pressure can be released from the autoclave without causing cracking, and that the maximum rate decreases as the gel size increases. Using an analysis developed in a companion paper, the stresses generated during depressurization are compared to the modulus of rupture of our aerogels. The calculations require knowledge of the pressure-dependence of the density of the vapor (ethanol, in our experiments), as well as the permeability and modulus of the gel network. Measurements of those properties were performed on a series of silica gels made under basic and neutral conditions. We find that the calculated stresses are large enough to account for the cracking of our gels at high rates of depressurization; moreover, the predicted dependence of stress on gel diameter is in agreement with experiment. 相似文献
953.
利用加捻纤维束的力学性能,可以制成预应力复合材料.在不受外力的情况下,这种复合材料的基体受压应力的控制.当有拉伸力作用的时候,材料所受的拉应力值会大大减少,这样,利用这种现象可以提高纤维增强复合材料的抗拉强度.本文将分析连续的加捻纤维束受拉状况并考虑到材料固化后产生的残余应力的影响.这种方法所产生的预应力取决于纤维束的加捻程度.本文将给出计算这种预应力的方法,而且还提供加捻纤维束产生预应力的光弹测试结果以及这种纤维预应力复合材料的纤维破坏的特征. 相似文献
954.
Neutron diffraction has been used to measure the crystallite orientation distribution function for a sample of rolled aluminium plate. Based on this study an expression is given for the ultrasonic velocity of the fundamental horizontally polarized shear (SH) wave propagating in the plane of the plate at an angle θ to the rolling direction. This expression is correct to second order in the leading texture component and is compared with the exact numerical result and with measurements of the SH wave velocity for this plate. In textured materials the group and phase velocities are not, in general, parallel and an expression for the angle between them is derived. Inclusion of this effect leads to better agreement between experiment and theory. The results have application to the texture-independent determination of stress with ultrasonics recently proposed by MacDonald and Thompson et al. 相似文献
955.
研究了500和600℃真空退火后的纳米晶Fe38.4Co40Si9B9Nb2.6Cu合金初始磁导率随温度的变化规律,发现较高温度(600℃)退火的FeCo基纳米晶合金,在非晶相居里温度以上较宽温度范围内磁导率没有明显的衰减,这是在双相纳米晶合金中观察到的一种新现象,其磁特性不同于Fe基纳米晶合金.为了探明这种现象的起源,估算了与剩余非晶相同成分的非晶合金的居里温度及纳米晶粒间发生交换耦合作用的参数
关键词:
交换耦合作用
非晶相居里温度
交换耦合穿透深度 相似文献
956.
基于α-和β-微区、微晶、交联和缠结链组网络结构和非线性粘弹性复相涨落模型,提出了双重(物理和力学)老化下不同尺寸和末端向量高分子链组的流动化微区内关联性局部化重排动力学新理论,它能把初级α-微区的降解作用和次级β-微区的再生效应对剪切速率、尺寸大小和温度依赖性有机结合起来.然后用统计力学和动力学结合法计算了三种不同类型高聚物在等温等压双重老化过程中多元链组的总构象改变自由能,证实了它起源于多元链组的尺寸大小、形状和体积的变化.推导出了它们单向拉伸下的本构方程、应力松弛模量和蠕变柔量表征式以及它们相对应的两组对比态普适方程.结果表明该两组对比态下应力松弛模量和蠕变柔量普适方程均具有同K-W-W伸展指数函数完全一致的形式.最终又建立了该两组对比态普适方程中三个分子参数同老化条件、温度和高聚物起始结构之间的相关性. 相似文献
957.
ZOU Wen-Hua TIAN Yuan SHEN Shui-Fa GU Jian-Zhong PENG Bang-Bao ZHANG Di-Da MA Zhong-Yu 《中国物理C(英文版)》2010,34(1)
Recent years have witnessed intense activity concerning the study of nuclei with equal numbers of neutrons and protons (N = Z). Exotic properties have been exhibited in the N = Z nuclei, especially in those with atomic masses around 80. In the present paper, the projected shell model(PSM)together with a relativistic Hartree-Bogoliubov (RHB) theory is used to study the nuclear structure near the N = Z line in the mass A ≈ 80 region. For three Zr isotopes 80,82,84Zr, the projected potential energy surfaces and ground state bands are calculated. It is shown that shape coexistence occurs in all of these nuclei. Moreover, we find that the residual neutron-proton interaction strongly affects the ground state band of 80Zr; however, it slightly modifies those of 82Zr and 84Zr. 相似文献
958.
YUAN KaiHua & QIU ZhiPing School of Aeronautic Science Engineering Beijing University of Aeronautics Astronautics Beijing China 《中国科学:物理学 力学 天文学(英文版)》2010,(2)
The flutter instability of stiffened composite panels subjected to aerodynamic forces in the supersonic flow is investigated. Based on Hamilton's principle,the aeroelastic model of the composite panel is established by using the von Karman large deflection plate theory,piston theory aerodynamics and the quasi-steady thermal stress theory. Then,using the finite element method along with Bogner-Fox-Schmit elements and three-dimensional beam elements,the nonlinear equations of motion are derived. The effect of... 相似文献
959.
应力为SGBVE分布强度为指数分布下结构可靠度的估计 总被引:3,自引:0,他引:3
考虑了应力服从SGBVE分布,强度服从指数分布的应力—强度模型,分别在应力参数未知和部分强度参数未知的情形下给出了该模型可靠度的估计,并讨论了其性质. 相似文献
960.
The asymptotic expressions of the covariance matrices for both the least square estimates
L
α
T
and Markov (best linear) estimates
are obtained, based on a sample in a finite interval (0, T) of the regression co-efficients α = (α
1, …, α
m
0)′ of a parameter-continuous process with a stationary residual. We assume that the regression variables φ
ν(t), t ⩾ 0, ν = 1, …, m
0, are continuous in t, and satisfy conditions (3.1)–(3.3). For the residual, we assume that it is a stationary process that possesses a bounded
continuous spectral density f(λ). Under these assumptions, it is proven that
where the matrices D
T
, B(0), α(λ) are defined in Section 3.
Under the assumptions mentioned above, if, furthermore, there exist some positive integer m and a constant C such that g(λ)(1 + λ
2)m ⩾ C > 0, where g(λ) is the spectral density of the residual, and for every N > 0,
converge uniformly in h, l ∈ (−N, N), then the following formula holds.
The asymptotic equivalence of the least square estimates and the Markov estimates is also discussed.
Translated by Wang Ting from the Chinese version of the paper published in Journal of Beijing Normal University (Natural Sciences), 1965, 1: 15–44 相似文献