疲劳设计方法的进展

本文对早期疲劳设计方法,包括无限寿命设计、安全寿命设计、破损-安全寿命设计、损伤容限设计作了简单的回顾,对可靠性设计新方法作了详尽描述,同时还对疲劳寿命估算中的名义应力法与局部应力应变法进行了比较,最后对今后这课题的研究提出了一些建议。

热网管道热损失现场测试方法探讨

<正> 国外热网管道热损失测试多半采用热流计、红外测温仪、点温计等测试手段来实现。但现场测试时往往受到风、日照等非稳态影响。为探讨现场测试方法的可行性,采用了热流计法、表面温度法、温差法和焓降法来测量热网管道热损失。a.热流计法:用热流计直接测量管道保温层外表面热损失。b.表面温度法:测量管道保温层外表面温度、环境温度和风速,按对流换热和辐射换热公式来计算管道热损失。c.温差法:根据管道保温层内、外表面温度,内、外径以及实验室测得的保温材料导热系数,按径向一维导热计

Simples nacional : Estatuto nacional da microempresa e da empresa de pequeno porte

Apresenta a Lei Complementar nº 123, de 14 de dezembro de 2006, que institui o Estatuto Nacional da Microempresa e da Empresa de Pequeno Porte; altera dispositivos das Leis nºs 8.212 e 8.213, ambas de 24 de julho de 1991, da Consolidação das Leis do Trabalho (CLT), aprovada pelo Decreto-Lei nº 5.452, de 1º de maio de 1943, da Lei nº 10.189, de 14 de fevereiro de 2001, da Lei Complementar nº 63, de 11 de janeiro de 1990; e revoga as Leis nºs 9.317, de 5 de dezembro de 1996, e 9.841, de 5 de outubro de 1999.

薄层放电的磁流体力学旋转流动分析

<正> 磁流体力学旋转流问题中一般假设流体输运系数为常数。用磁流体力学方法处理电弧放电问题时,经常假设弧柱內外的输运系数分别为两个不同的常数,并取弧柱外介质的电导率为零。在气态裂变反应堆、核火箭及重元素的同位素分离器中,广泛采用交叉电磁场的方法产生等离子体的高速旋转流动。文献[8,9]研究了薄层放电的电磁驱动装置,用多对极实验得到一定的分离效果。可以认为,这类薄层放电的电流集中在

A finite deformation analysis of polycrystal by considering the influence of grain boundary

By combining grain boundary (GB) and its influence zone, a micromechanic model for polycrystal is established for considering the influence of GB. By using the crystal plasticity theory and the finite element method for finite deformation, numerical simulation is carried out by the model. Calculated results display the microscopic characteristic of deformation fields of grains and are in qualitative agreement with experimental results.

A stochastic jump and deterministic dynamics model of impact failure evolution with rate effect

Motivated by the observation of the rate effect on material failure, a model of nonlinear and nonlocal evolution is developed, that includes both stochastic and dynamic effects. In phase space a transitional region prevails, which distinguishes the failure behavior from a globally stable one to that of catastrophic. Several probability functions are found to characterize the distinctive features of evolution due to different degrees of nucleation, growth and coalescence rates. The results may provide a better understanding of material failure.

Crack growth by grain boundary cavitation in the transient and extensive creep regimes

Crack growth due to cavity growth and coalescence along grain boundaries is analyzed under transient and extensive creep conditions in a compact tension specimen. Account is taken of the finite geometry changes accompanying crack tip blunting. The material is characterized as an elastic-power law creeping solid with an additional contribution to the creep rate arising from a given density of cavitating grain boundary facets. All voids are assumed present from the outset and distributed on a given density of cavitating grain boundary facets. The evolution of the stress fields with crack growth under three load histories is described in some detail for a relatively ductile material. The full-field plane strain finite element calculations show the competing effects of stress relaxation due to constrained creep, diffusion and crack tip blunting. and of stress increase due to the instantaneous elastic response to crack growth. At very high crack growth rates the Hui-Riedel fields dominate the crack tip region. However. the high growth rates are not sustained for any length of time in the compact tension geometry analyzed. The region of dominance of the Hui-Riedel field shrinks rapidly so that the near-tip fields are controlled by the HRR-type field shortly after the onset of crack growth. Crack growth rates under various conditions of loading and spanning the range of times from small scale creep to extensive creep are obtained. We show that there is a strong similarity between crack growth history and the behaviour of the C(t) and C(t) parameters. so that crack growth rates correlate rather well with C(t) and C(t). A relatively brittle material is also considered that has a very different near-tip stress field and crack growth history.

The influence of momentum addition on the acceleration of the solar and stellar winds

The influence of the momentum addition, which may be associated with the average or fluctuation transverse component of the magnetic field or others, on the acceleration the solar wind or stellar wind is studied in a local streamtube. The results show that the larger the momentum addition the stronger the acceleration of the wind. For example, if the typical transverse magnetic field is about 0.1 of the longitudinal field, the velocity of the solar wind at 1 AU may be increased by 40%. The coronal hole may be considered as a streamtube, the presence of a high stream from the coronal hole may be explained by the existence of an average or fluctuation transverse magnetic field in the streamtube. A similar conclusion may be applied to the polar region, where the velocity of the solar wind will be larger than elsewhere as if there is a transverse component of magnetic field, as well as to the stellar wind. The influence of other parameters on the acceleration of the solar wind is also discussed. From the viewpoint of the solar wind mechanism, the present paper shows that the momentum addition in the subsonic flow region can increase the velocity of the solar wind at 1 AU.

PICES Press, Vol. 7, No. 1, January 1999

Taking stock and looking to the future - note from former PICES Chairman The state of the western North Pacific in the first half of 1998 The status of the Bering Sea in the first eight month of 1998 The state of the eastern North Pacific since February 1998 Highlights of PICES VII, review of SB activities and future workplan The second PICES Workshop on the Okhotsk Sea and ajacent area PICES-GLOBEC Climate Change and Carrying Capacity Program: A report from PICES VII Data management for the CCCC Program Report on GOOS Living Marine Resource Panel Meeting Photos from PICES VII Vjatcheslav Petrovich Shuntov GLOBEC Canada: Who we are, what we’ve been doing and where we’re headed The Ocean Carrying Capacity Research Program (OCC) at the Alaska Fisheries Science Center, Auke Bay Laboratory, Juneau, Alaska JAMSTEC research activities in the northern North Pacific People and events

¿Es tan perjudicial la televisión que ven los jóvenes y adolescentes?

[Es] En este trabajo se presentan los resultados de un estudio piloto realizado en la Comunidad Autónoma del País Vasco con una muestra de sujetos con edades comprendidas entre 12 y 40 años. Dentro de una investigación más amplia donde se pretende relacionar la dieta televisiva y los valores implícitos y explícitos que se perciben en los contenidos televisivos, se exponen algunas diferencias y semejanzas respecto a los hábitos y dieta televisiva de los diferentes grupos de edad. Los datos encontrados nos permiten concluir que los programas más visionados no son los más perniciosos para adolescentes y jóvenes, ni tampoco que el visionado de la televisión impida el desarrollo de otro tipo de actividades.