A brief history of fractography

Fracture surfaces have, no doubt, been studied throughout the history of mankind, probably starting with observations on stone-age tools. In the 16th to 18th centuries, the macroscopic appearance of fracture surfaces was used to assess the quality of metallic materials, with studies by Réaumur in 1722 being the most notable. However, it was not until 1943 that fracture surfaces were first examined at high magnifications (using optical microscopy up to 1000 ×), and that the first attempts were made to examine replicas of fracture surfaces using transmission electron microscopy (TEM). Early replicas had poor fidelity and resolution, and it was not until 1956 that Crussard et al. pioneered high-resolution TEM fractography using shadowed, direct-carbon replicas. This technique (and its subsequent variations) revolutionized fractography and led to a plethora of studies in the 1960's and 70's. It therefore seems appropriate to commemorate the 50th anniversary of high-resolution electron fractography with a review of how it, and subsequent scanning electron microscopy (SEM) and other techniques, have led to a better understanding of fracture processes. Such understanding has been invaluable in failure analysis and in developing improved materials. Milestone observations for a number of important models of fracture in inert environments including cleavage, brittle intergranular fracture, dimpled overload fractures, and fatigue fractures, are described first, followed by examples of key observations for fractures produced in embrittling environments.     

A mathematical model for the prediction of temperature in a dry snow layer

A mathematical model for predicting the temperature in a homogeneous layer of dry snow is presented. The model, which is physically based, is capable of predicting diurnal temperature behaviour at the snow surface and at any depth within a snow layer given the variation in a limited set of meteorological parameters over that period. A sensitivity analysis is performed to determine the important parameters in the prediction of snow surface temperatures. These are found to be consistent with simple physical reasoning.     

A mathematical model for the prediction of volume change cracking in end-restrained concrete members

A mathematical model for the prediction of volume change cracking in end-restrained concrete members has been developed. The model adopted the ACI Committee 209 method for the prediction of creep and shrinkage of concrete in conjunction with the bond slip cracking mechanism with an improved tensile strain distribution. The time discretization method was used for calculating the development of shrinkage and creep in concrete, taking into consideration the daily variations in temperature and relative humidity. Before-cracking and after-cracking creep of concrete were also calculated, for the first time, taking into consideration the variable stress level to which the concrete section is exposed. The results of tensile strain development, cracking age and crack width development obtained from the proposed model were compared with those obtained from a previous experimental research program which used a test model that largely resembled site conditions. The two results were found to be in line with one another, which proves the feasibility of the proposed model.

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Résumé On a élaboré un modèle mathématique pour la prédiction de la fissuration due au changement de volume des éléments en béton encastrés sur leurs extrémités. Ce modèle adopte la Méthode ACI 209 pour la prédiction du fluage et du retrait du béton conjugés au mécanisme de fissuration due à la défaillance de l'adhérence avec une amélioration de la distribution de la résistance à la traction. Le calcul du développement du retrait et du fluage a été fait en fonction du temps et a tenu compte des variations de température et d'humidité relative. Le fluage, avant et après fissuration, a été calculé également, en tenant compte, pour la première fois, du niveau de contrainte variable auquel est exposé l'élément en béton. Les résultats obtenus de ce modèle proposé sur le développement de la contrainte de traction, l'age de fissuration et le développement en largueur des fissures ont été comparés à ceux provenant d'une recherche expérimentale précédente utilisant un modèle d'essai, qui ressemble aux conditionsin situ. Les deux méthodes ont donné des résultats concordants, ce qui valide le modèle proposé.

     

A new mathematical model for irradiance field prediction of upper-room ultraviolet germicidal systems

There has been an increasing interest in the use of upper-room ultraviolet germicidal irradiation (UVGI) system because of its proven disinfection effect for airborne microorganisms. To better design and explore further potential applications of UVGI systems, it is of critical importance to predict the spatial UV intensity in enclosures. In this paper, we developed a new mathematical model to predict spatial radiation intensity for upper-room ultraviolet germicidal irradiation systems. The detail geometries of the lamp and the reflector were removed and replaced by introducing a fictitious irradiation surface near louver slots. The view factor approach was applied to evaluate the UV irradiance in a three-dimensional space with different louver configurations. With this approach no detail meshing of the fixture is required and this leads to significant simplification of the entire systems from modeling perspectives. To validate the model, experiments were performed in a full-scale environmental controlled chamber in which one UVGI fixture was mounted on a sidewall. The UV irradiance was measured by a radiometer. The results predicted by the present model agree very well with the experimental measurements. Factors affect the accuracy of the model was also discussed.     

50th Birthday of O. E. Andreikiv

50th Birthday of O. E. Andreikiv     

Reliability prediction: A constructive critique of MIL-HDBK-217E

MIL-HDBK-217E is based on some major fallacies and oversimplifications. These include the assumption of constant failure rate, the assumed independence of the Pi factors, the oversimplification of temperature dependence, the neglect of process yield and screening fall-out as determinants in the categorization of quality grade and the absence of manufacturing date information. These weaknesses are discussed and some recommendations made.     

Discussion of a paper by E. O. Frind

In a recent paper, Dr. Frind has formulated a two-dimensional isoparametric finite element based upon the Hermite bicubic interpolation scheme. The present discussion focuses upon certain simplifications in the derivation which appear to have diminished the accuracy of the resulting element, and suggests a simpler approach to the element formulation. This author agrees strongly with Dr. Frind's recommendation of the Hermite parametric element as an efficient and useful tool for general field problems; the present comments are offered to point out that, in fact, the accuracy comparisons presented by Dr. Frind are biased against the Hermite finite element.     

A mathematical model for the prediction of water vapour transmission rate at different temperature and relative humidity combinations

A simple mathematical procedure for the estimation of water vapour transmission rate under different conditions is presented and discussed. The ASTM dynamic and gravimetric methods were used for measuring the water vapour transmission rate of four thin plastic films (PET 19 μm, PVC 16 μm, EVA 15 μm and LDPE 23 μm) under 38 different conditions of temperature and relative humidity and the corresponding permeance values were drawn. On the basis of the Clausius Clapeyron's relationship between temperature and water vapour pressure, a simple equation was derived for a rapid transformation of water vapour transmission rate data. The mathematical procedure was applied to the data collected for the four thin films and good agreement was found between observed and predicted values for the PET and LDPE films, while for the PVC and EVA films the equation developed led to an overestimate of water vapour transmission at the lower temperatures.     

炭材料科学的研究现状和发展趋势——Carbon 2006参会感

每年一度的国际炭会议（Carbon 2006）于2006年7月16至21日在英国苏格兰北部的海滨城市阿伯丁（Aberdeen）召开。本届会议由英国炭学会承办。来自世界各地约500位学者参加了这次会议。其中来自英国、西班牙、日本、美国、法国、德国的与会代表人数较多。此次来自中国大陆的参会代表也超过30人，基本上国内从事炭材料科学研究的高校和科研机构均有代表参会。这说明国内的科研工作者已经意识到国际交流在科学研究中的重要性，正积极加强与外界的学术交流与互动。另外还有十余位在海外留学和工作的中国学者参加了本届炭会议。中国人正逐步走上炭材料科学研究的国际舞台，在这一领域发挥着越来越重要的作用。     

炭科学技术的研究现状与发展趋势——记Carbon 2007国际炭会议

2007年国际炭会议（Carbon 2007）于7月15至20日在美国西海岸城市西雅图举行，主办者为美国炭素学会，承办方为橡树岭国家实验室（Oak Ridge National Lab）炭材料技术研究组。     

浅谈城市与街道空间

本文主要是从城市与街道的发展,城市与街道空间方面来初步探讨城市与街道空间之间的关系,城市与街道的发展,主要从其产生、中西方城市与街道形态发展,现代城市和街遘的发展趋势几方面来体现,城市与街道空间则主要从街道空间在城市中的地位,街道空间的构成和分类几方面来说明两者之间的关系.本文将为街道空间公共设施设计研究提供一个参考.     

Design and manufacture of high precision strain gauge dynamometers and balances at the O.N.E.R.A. Modane Centre

The Modane–Avrieux Large Wind Tunnel Department of O.N.E.R.A. designs equips and calibrates single or multi–component dynamometers and balances for tests in its own facilities. It also undertakes such work as requested by external organisations. The capacities of these instruments range from 0.01 N (0.002 Ibf) to 1 000 kN (100 tonf) and the general accuracy is of the order of 10–3.
The principles and processes governing the design, fabrication and calibration of these transducers are described.     

A geological history of reflecting optics.

Optical reflectors in animals are diverse and ancient. The first image-forming eye appeared around 543 million years ago. This introduced vision as a selection pressure in the evolution of animals, and consequently the evolution of adapted optical devices. The earliest known optical reflectors--diffraction gratings--are 515 Myr old. The subsequent fossil record preserves multilayer reflectors, including liquid crystals and mirrors, 'white' and 'blue' scattering structures, antireflective surfaces and the very latest addition to optical physics--photonic crystals. The aim of this article is to reveal the diversity of reflecting optics in nature, introducing the first appearance of some reflector types as they appear in the fossil record as it stands (which includes many new records) and backdating others in geological time through evolutionary analyses. This article also reveals the commercial potential for these optical devices, in terms of lessons from their nano-level designs and the possible emulation of their engineering processes--molecular self-assembly.     

A brief tutorial on the estimation of the process standard deviation

We consider the common SQC problem of estimating a process standard deviation based on several sample ranges or sample standard deviations. Simple, well-known facts that are used to produce “control chart constants” can also provide guidance in the combining of such ranges or standard deviations for normal processes. Root mean squared errors for both unbiased linear estimators common in the literature and some (biased) optimal estimators are shown to be simple functions of these constants.