The size-dependent bending elastic properties of nanobeams with surface effects

A theoretical model is presented to investigate the size-dependent bending elastic properties of a nanobeam with the influence of the surface relaxation and the surface tension taken into consideration. The surface layer and its thickness of a nanostructure are defined unambiguously. A three-dimensional (3D) crystal model for a nanofilm with n layers of relaxed atoms is investigated. The four nonzero elastic constants of the nanofilm are derived, and then the Young's modulus for simple tension is obtained. Using the relation of energy equilibrium, the size-dependent effective elastic modulus and effective flexural rigidity of a nanobeam with two kinds of cross sections are derived, and their dependence on the surface relaxation and the surface tension is analysed.

Small scale, grain size and substrate effects in nano-indentation experiment of film-substrate systems

The mechanical properties of film-substrate systems have been investigated through nano-indentation experiments in our former paper (Chen, S.H., Liu, L., Wang, T.C., 2005. Investigation of the mechanical properties of thin films by nano-indentation, considering the effects of thickness and different coating-substrate combinations. Surf. Coat. Technol., 191, 25-32), in which Al-Glass with three different film thicknesses are adopted and it is found that the relation between the hardness H and normalized indentation depth h/t, where t denotes the film thickness, exhibits three different regimes: (i) the hardness decreases obviously with increasing indentation depth; (ii) then, the hardness keeps an almost constant value in the range of 0.1-0.7 of the normalized indentation depth h/t; (iii) after that, the hardness increases with increasing indentation depth. In this paper, the indentation image is further investigated and finite element method is used to analyze the nano-indentation phenomena with both classical plasticity and strain gradient plasticity theories. Not only the case with an ideal sharp indenter tip but also that with a round one is considered in both theories. Finally, we find that the classical plasticity theory can not predict the experimental results, even considering the indenter tip curvature. However, the strain gradient plasticity theory can describe the experimental data very well not only at a shallow indentation depth but also at a deep depth. Strain gradient and substrate effects are proved to coexist in film-substrate nano-indentation experiments. (c) 2006 Elsevier Ltd. All rights reserved.

Effect of grain size on slow fatigue crack propagation and plastic deformation near crack tip

Fatigue crack growth and its threshold are investigated at a stress ratio of 0.5 for the three-point bend specimen made of Austenitic stainless steel. The effect of grain size on the crack tip plastic deformation is investigated. The results show that the threshold value Δkth increases linearly with the square root of grain size d and the growth rate is slower for materials with larger grain size. The plastic zone size and ratio for different grain sizes are different at the threshold. The maximum stress intensity factor is kmax and σys is the yield strength. At the same time, the characteristics of the plastic deformation development is discontinuous and anti-symmetric as the growth rate is increased from 2·10—8 to 10−7 mm/cycle.

Litter dynamics and phenology of Melaleuca quinquenervia in south Florida

We monitored litterfall biomass at six different sites of melaleuca (Melaleuca quinquenervia (Cav.) S.T. Blake) forested wetlands in South Florida from July 1997 to June 1999. Annual litterfall of melaleuca varied between sites from 6.5 to 9.9 t dry wt ha(-1) yr(1) over the two-year period. Litterfall was significantly higher (p < 0.0001) in scasonally flooded habitats (9.3 t ha(-1) yr(1)) than in non-flooded (7.5 t ha(-1) yr(1)) and permanently flooded habitats (8.0 t ha(-1) yr(1)). Leaf fall was the major component forming 70% of the total litter, woody material 16%, and reproductive material 11%. Phenology of flowering and leaf flush was investigated by examination of the timing and duration of the fall of different plant parts in the litter traps, coupled with monthly field observations during the two-year study. In both years, flowering began in October and November, with peak flowers production around December, and was essentially completed by February and March. New shoot growth began in mid winter after peak flowering, and extended into the spring. Very little new growth was observed in melaleuca forests during the summer months, from May to August, in South Florida. In contrast, the fall of leaves and small wood was recorded in every month of the year, but generally increased during the dry season with higher levels observed from February to April. Also, no seasonality was recorded in the fall of seed capsules, which apparently resulted from the continual self-thinning of small branches and twigs inside the forest stand. In planning management for perennial weeds, it is important to determine the period during its annual growth cycle when the plant is most susceptible to control measures. These phenological data suggest that the appropriate time for melaleuca control in South Florida might be during late winter and early spring, when the plant is most active.

Control of Large-size SiC Growth Process Using Modeling tool

Large size bulk silicon carbide (SiC) crystals are commonly grown by the physical vapor transport (PVT) method. The PVT growth of SiC crystals involves sublimation and condensation, chemical reactions, stoichiometry, mass transport, induced thermal stress, as well as defect and micropipes generation and propagation. The quality and polytype of as-grown SiC crystals are related to the temperature distribution inside the growth chamber during the growth process, it is critical to predict the temperature distribution from the measured temperatures outside the crucible by pyrometers. A radio-frequency induction-heating furnace was used for the growth of large-size SiC crystals by the PVT method in the present study. Modeling and simulation have been used to develop the SiC growth process and to improve the SiC crystal quality. Parameters such as the temperature measured at the top of crucible, temperature measured at the bottom of the crucible, and inert gas pressure are used to control the SiC growth process. By measuring the temperatures at the top and bottom of the crucible, the temperatures inside the crucible were predicted with the help of modeling tool. SiC crystals of 6H polytype were obtained and characterized by the Raman scattering spectroscopy and SEM, and crystals of few millimeter size grown inside the crucible were found without micropipes. Expansion of the crystals were also performed with the help of modeling and simulation.

Influence of Wind and Grain Size on Migration of Asymmetric Sand Waves

Large parts of shallow seas are covered by regular seabed patterns and sand wave is one kind of these patterns. The instability of the sedimentary structures may hazard pipelines and the foundations of offshore structures. In the last decade or so, it's a focus for engineers to investigate the movement mechanism of sand waves. Previous theoretical studies of the subject have developed a general model to predict the growth and migration of sand waves, which is based on the two-dimensional vertical shallow water equations and the bed-form deformation equations. Although the relation between wave-current flow and sand bed deformation has been established, the topographic influence has not been considered in the model. In this paper some special patterns, which are asymmetric and close to the reality, are represent as the perturbed seabed and the evolution of sand waves is calculated. The combination of a steady flow induced by wind and a sinusoidal tidal flow is considered as the basic flow. Finally the relations of some parameters (grain size, etc.) and sand waves' growth and migration are discussed, and the growth rate and migration speeds of asymmetric sand waves are carried out.

Size composition of catches of Yellowfin tuna in the Japanese long-line fishery in the eastern tropical Pacific east of 130°W

ENGLISH (pgs. 267-283): In the spring of 1963, the senior author, who is a member of the staff of the Nankai Regional Fisheries Research. Laboratory, Fisheries Agency, Japanese Government, came to the Institute of Marine Resources of the University of California as a visiting investigator, bringing with him catch statistical data from the fishery in the eastern Pacific, which had been collected at the Nankai Regional Fisheries Research Laboratory (NRFRL) through September 1962, in order to conduct studies of these data in collaboration with the junior author, and with investigators of the InterAmerican Tropical Tuna Commission. A general review of the long-line fishery, based on the catch statistics of the commercial fishing fleet has been published by Suda and Schaefer (1965). In this paper we present an analysis of data respecting the size-composition of yellowfin tuna taken on long-line gear throughout the eastern Pacific between 1958 and 1962, and make some comparisons with data on size-composition of yellowfin tuna taken in the near-surface fishery, by bait boats and purse-seiners, in waters adjacent to the American coast. As has been shown by Suda and Schaefer (1965), the long-line fishery in the eastern Pacific is primarily directed toward the capture of bigeye tuna. However, considerable quantities of yellowfin tuna are also taken on this gear, and, in addition, there are substantial catches of albacore and of several species of spearfishes in some parts of the range of this fishery. Information respecting the catch rates of yellowfin tuna, and information respecting the size-composition of the stock of yellowfin tuna being exploited by the long-line fishery, is of particular interes~" because the yellowfin tuna population of the eastern Pacific is also subject to an intensive fishery by baitboats and purse-seiners which capture this species, together with skipjack, near the surface along the coast of the Americas, and around the outlying islands, in the region of California to northern Chile. SPANISH (pgs. 311-329): En la primavera de 1963, el autor principal, quien es miembro del personal del Nankai Regional Fisheries Research Laboratory, Fisheries Agency del gobierno japonés, vino al Institute of Marine Resources de la Universidad de California en calidad de investigador visitante y trajo consigo datos estadísticos de las capturas de la pesquería en el Pacífico oriental, que habían sido recolectados en el Nankai Regional Fisheries Research Laboratory (NRFRL) hasta septiembre de 1962, con el fin de hacer estudios de esos datos en colaboración con el coautor y con investigadores de la Comisión Interamericana del Atún Tropical. Una revisión general de la pesquería con palangre, basada sobre las estadísticas de captura de la flota pesquera comercial, ha sido publicada por Suda y Schaefer (1965). En este trabajo presentamos un análisis de los datos correspondientes a la composición de tamaños del atún aleta amarilla capturado con equipo palangrero en todo el Pacífico oriental, entre 1958 y 1962, y hacemos algunas comparaciones con los datos sobre la composición de tamaños del atún aleta amarilla cogido en la pesquería superficial cercana, por barcos de carnada y rederos en aguas adyacentes a la costa americana. Como ha sido demostrado por Suda y Schaefer (1965) la pesquería con palangre en el Pacífico oriental tiene como principal objeto la captura del atún ojo grande. Sin embargo, considerables cantidades de atún aleta amarilla son capturadas también por este equipo y, además, hay también considerables capturas de albacora y de diversas especies de peces-espada en algunas partes de la región que abarca esta pesquería. La información respecto a las tasas de captura del atún aleta amarilla, y la relativa a la composición de tamaños del stock de esta especie que explota la pesquería con palangre, es de particular interés, a causa de que la población de atún aleta amarilla del Pacífico oriental es también objeto de una pesca intensiva por barcos de carnada y rederos que capturan esta especie, junto con el barrilete, cerca de la superficie a 10 largo de la costa de las Américas y alrededor de las islas mar afuera, en la región desde California hasta el norte de Chile.

Edge and Size Effects in Micro Composite Structure

Because of the load transfer effect of interface layer, the stress distribution inside the composite structure of film/substrate can be very different from the Timoshenko's model. In this paper, we give the derivation and analysis of such load transfer effect of shear-lag (S-L) model. The micro-structure size (boundary conditions) effect together with interface load transfer effect becomes more and more important as the microstructure size including the three dimensions of thickness, width and length shrinks. The microstructure size is also responsible for the so-called edge-induced stress. The edge effect and difference of S-L model and Timoshenko model are also demonstrated.