Singularity of dynamic stress fields around an interface crack between viscoelastic bodies

The singular nature of the dynamic stress fields around an interface crack located between two dissimilar isotropic linearly viscoelastic bodies is studied. A harmonic load is imposed on the surfaces of the interface crack. The dynamic stress fields around the crack are obtained by solving a set of simultaneous singular integral equations in terms of the normal and tangent crack dislocation densities. The singularity of the dynamic stress fields near the crack tips is embodied in the fundamental solutions of the singular integral equations. The investigation of the fundamental solutions indicates that the singularity and oscillation indices of the stress fields are both dependent upon the material constants and the frequency of the harmonic load. This observation is different from the well-known -1/2 oscillating singularity for elastic bi-materials. The explanation for the differences between viscoelastic and elastic bi-materials can be given by the additional viscosity mismatch in the case of viscoelastic bi-materials. As an example, the standard linear solid model of a viscoelastic material is used. The effects of the frequency and the material constants (short-term modulus, long-term modulus and relaxation time) on the singularity and the oscillation indices are studied numerically.

Computer simulation on the collision-sticking dynamics of two colloidal particles in an optical trap

Collisions of a particle pair induced by optical tweezers have been employed to study colloidal stability. In order to deepen insights regarding the collision-sticking dynamics of a particle pair in the optical trap that were observed in experimental approaches at the particle level, the authors carry out a Brownian dynamics simulation. In the simulation, various contributing factors, including the Derjaguin-Landau-Verwey-Overbeek interaction of particles, hydrodynamic interactions, optical trapping forces on the two particles, and the Brownian motion, were all taken into account. The simulation reproduces the tendencies of the accumulated sticking probability during the trapping duration for the trapped particle pair described in our previous study and provides an explanation for why the two entangled particles in the trap experience two different statuses. (c) 2007 American Institute of Physics.

优化研究所内部环境的初步尝试

<正>力学所成立已34年,目前职工总人数逾800人,是力学科学的综合性研究大所。它面临着课题分散、人员及设备老化、资金紧张、住房紧张等一系列问题。如何走出困境,如何进一步完善综合性研究大所的运转机制,在竞争中寻求自身的生存与发展,是有待深入讨论研究和急需解决的重要问题。近年来,力学所在这些方面也进行了初步的探索和尝试。一、适当调整内部科研组织结构,建立跨室联合研究集体,增强研究所的竞争力和自身发展能力力学所原有13个研究室,基本上是按力学分支学科划分建立起来的,主要研究领域包括爆炸力学、物理力学、磁流力学和等离子体动力学、土力学、高速气体动力学、流体力学、空气动力学、高温气体动力学、固体力学、激光流体物理、跨声速空气动力学、材料力学性质、微重力科

用蒙特卡罗方法研究混合物模型

本文用蒙特卡罗方法计算了五种高密度二元混合物的压缩因子,并与两种解析的混合物模型的计算值进行了比较,结果表明单液范德瓦尔斯混合物模型的计算值更接近于蒙特卡罗方法的结果。

第2届全国疲劳学术会议

<正> 中国力学学会、中国航空学会、中国机械工程学会联合召开的第2届全国疲劳学术会议,于1984年10月8—11日在四川峨眉西南交通大学举行,参加会议代表150多人,宣读和交流126篇论文,并进行了专题讨论,论文内容大致包括以下几个方面。

Mulher, política e ação

Traz um relato do trabalho desenvolvido pela Comissão Especial destinada ao estudo das medidas legislativas que visem implementar, no Brasil, as decisões da IV Conferência Mundial da Mulher.

O papel da energia nas ações de mitigação

Descreve as alternativas energéticas que se colocam para mitigar boa parte das emissões de gases de efeito estufa (GEE) do planeta. Enfatiza o potencial para o uso mais eficiente da energia em todos os setores da economia e nas oportunidade de substituição de combustíveis fósseis por combustíveis renováveis. Ressalta a importância de mudança de hábitos de consumo para reduzir as emissões de GEE a níveis considerados seguros, de maneira a se estabilizarem as concentrações de gases na atmosfera em níveis suficientemente baixos.

正交设计在疲劳试验中的应用

<正> 引言到目前为止,疲劳的机理和基本理论(包括累积损伤理论、裂纹扩展理论、剩余强度理论等)仍然没有得到解决,主要是靠实验来解决问题。但是,进行疲劳试验,存在许多实际的问题。首先,影响疲劳强度的因素很多,比如试件的形状和尺寸、试件表面状况、应力集中、热处

Analysis of flexural vibration of viscoelastically damped sandwich plates

The simplified governing equations and corresponding boundary conditions of flexural vibration of viscoelastically damped unsymmetrical sandwich plates are given. The asymptotic solution of the equations is then discussed. If only the first terms of the asymptotic solution of all variables are taken as an approximate solution, the result is identical with that obtained from the Modal Strain Energy (MSE) Method. As more terms of the asymptotic solution are taken, the successive calculations show improved accuracy. With the natural frequencies and the modal loss factors of a damped sandwich plate known, one can calculate the response of the plate to various loads providing a reliable basis for engineering design.

[Discurso do Deputado Valério Magalhães : Sessão da Câmara dos Deputados de 14 de agosto de 1964]

Referência à palestra do economista Hélio Beltrão, cujo objetivo foi de despertar os setores responsáveis pela consolidação de Brasília. Condenação ao retorno de diversos órgãos federais para o Rio de Janeiro. Cita o artigo "Política de contenção" publicado no jornal Correio Braziliense sobre normas do Ministro da Fazenda que implicam na redução das verbas consignadas ao Distrito Federal.