Fracture behavior of axisymmetrical bars under high triaxial stress and large strain cyclic loading

Axisymmetric notched bars with notch roots of large and small radii were tested under large strain cyclic loading. The main attention is focused on the fracture behaviour of steels having cycles to failure within the range 1-100. Our study shows that a gradual transition from a static ductile nature to one of fatigue cleavage can be observed and characterized by the Coffin-Manson formula in a generalized form. Both the triaxial tensile stress within the central region of specimens and static damage caused by the first increasing load have effects on the final failure event. A generalized cyclic strain range parameter DELTAepsilon is proposed as a measure of the numerous factors affecting behaviour. Fractographs are presented to illustrate the behaviour reported in the paper.

High Power 940 nm Al-free Active Region Laser Diodes and Bars with a Broad Waveguide

The 940 nm Al-free active region laser diodes and bars with a broad waveguide were designed and fabricated. The stuctures were grown by metal organic chemical vapour deposition. The devices show excellent performances. The maximum output power of 6.7 W in the 100 f^m broad-area laser diodes has been measured, and is 2. 5 times higher than that in the Al-containing active region laser diodes with a narrow waveguide and 1. 7 times higher than that in Al-free active region laser diodes with a narrow waveguide. The 19 % fill-factor laser diode bars emit 33 W, and they can operate at 15W with low degradation rates.

Preparation of stir bars for sorptive extraction using sol-gel technology

A sol-gel coating method for the preparation of extractive phase on bars used in sorptive microextraction is described. The extraction phase of poly(dimethylsiloxane) is partially crosslinked with the sol-gel network, and the most part is physically incorporated in the network. Three aging steps at different temperatures are applied to complete the crosslinking process. Thirty-micrometer-thick coating layer is obtained by one coating process. The improved coating shows good thermal stability up to 300degreesC. Spiked aqueous samples containing n-alkanes, polycyclic aromatic hydrocarbons and organophosphorus pesticides were analyzed by using the sorptive bars and GC. The results demonstrate that it is suitable for both aploar and polar analytes. The detection limit for chrysene is 7.44 ng/L, 0.74 ng/L for C-19 and 0.9 ng/L for phorate. The extraction equilibration can be reached in less than 15 min by supersonic extraction with the bars of 30 mum coating layer. (C) 2004 Elsevier B.V. All rights reserved.

Digital regionalization of geomorphology in Xinjiang

National Natural Science Foundation of China [40871177]; Project of State Key Lab of Resources and Environmental Information System [088RA304SA]; CAS Knowledge Innovation Project

Tectonic geomorphology of the Ryukyu Trench-Arc-Backarc System: geological-geophysical exploration and mapping

OKINAWA TROUGH; BASIN

Geomorphology, sedimentary processes and development of the Zenisu deep-sea channel, northern Philippine Sea

The Zenisu deep-sea channel originates on the Izu-Ogasawara island arc, and disappears in the Shikoku Basin of the Philippine Sea. The geomorphology, sedimentary processes, and the development of the Zenisu deep-sea channel were investigated on the basis of swath bathymetry, side-scan sonar imagery, submersible observations, and seismic data. The deep-sea channel can be divided into three segments according to the downslope gradient and channel orientation. They are the Zenisu Canyon, the E-W fan channel, and the trough-axis channel. The sediment fill is characterized by turbidite and debrite deposition and blocky-hummocky avalanche deposits on the flanks of the Zenisu Ridge. In the Zenisu Canyon and the Zenisu deep-sea channel, sediment transport by turbidity currents generates sediment waves (dunes) observed during the Shinkai 6500 dive 371. The development of the Zenisu Canyon is controlled by a N-S shear fault, whereas the trough-axis channel is controlled by basin subsidence associated with the Zenisu Ridge. The E-W fan channel was probably affected by the E-W fault and the basement morphology.

Dynamic properties and asymmetry of tension and compression of metal matrix composites under impact loading

The mechanical behaviors of 2124, Al-5Cu, Al-Li and 6061 alloys reinforced by silicon carbide particulates, together with 15%SiCw/6061 alloy, were studied under the quasi-static and impact loading conditions, using the split Hopkinson tension/compression bars and Instron universal testing machine. The effect of strain rate on the ultra tensile strength (UTS), the hardening modulus and the failure strain was investigated. At the same time, the SEM observations of dynamic fracture surfaces of various MMC materials showed some distinguished microstructures and patterns. Some new characteristics of asymmetry of mechanical behaviors of MMCs under tension and compression loading were also presented and explained in details, and they could be considered as marks to indicate, to some degree, the mechanism of controlling damage and failure of MMCs under impact loading. The development of new constitutive laws about MMCs under impact loading should benefit from these experimental results and theoretical analysis.

Wind Tunnel Experimental Investigation Of Sand Velocity In Aeolian Sand Transport

Sand velocity in aeolian sand transport was measured using the laser Doppler technique of PDPA (Phase Doppler Particle Analyzer) in a wind tunnel. The sand velocity profile, probability distribution of particle velocity, particle velocity fluctuation and particle turbulence were analyzed in detail. The experimental results verified that the sand horizontal velocity profile can be expressed by a logarithmic function above 0.01 in, while a deviation occurs below 0.01 m. The mean vertical velocity of grains generally ranges from -0.2 m/s to 0.2 m/s, and is downward at the lower height, upward at the higher height. The probability distributions of the horizontal velocity of ascending and descending particles have a typical peak and are right-skewed at a height of 4 turn in the lower part of saltation layer. The vertical profile of the horizontal RMS velocity fluctuation of particles shows a single peak. The horizontal RMS velocity fluctuation of sand particles is generally larger than the vertical RMS velocity fluctuation. The RMS velocity fluctuations of grains in both horizontal and vertical directions increase with wind velocity. The particle turbulence intensity decreases with height. The present investigation is helpful in understanding the sand movement mechanism in windblown sand transport and also provides a reference for the study of blowing sand velocity. (C) 2007 Elsevier B.V All rights reserved.

Reconstructing The Vertical Distribution Of The Aeolian Saltation Mass Flux Based On The Probability Distribution Of Lift-Off Velocity

The probability distribution of lift-off velocity of the saltating grains is a bridge to linking microscopic and macroscopic research of aeolian sand transport. The lift-off parameters of saltating grains (i.e., the horizontal and vertical lift-off velocities, resultant lift-off velocity, and lift-off angle) in a wind tunnel are measured by using a Phase Doppler Particle Analyzer (PDPA). The experimental results show that the probability distribution of horizontal lift-off velocity of saltating particles on a bed surface is a normal function, and that of vertical lift-off velocity is an exponential function. The probability distribution of resultant lift-off velocity of saltating grains can be expressed as a log-normal function, and that of lift-off angle complies with an exponential function. A numerical model for the vertical distribution of aeolian mass flux based on the probability distribution of lift-off velocity is established. The simulation gives a sand mass flux distribution which is consistent with the field data of Namikas (Namikas, S.L., 2003. Field measurement and numerical modelling of acolian mass flux distributions on a sandy beach, Sedimentology 50, 303-326). Therefore, these findings are helpful to further understand the probability characteristics of lift-off grains in aeolian sand transport. (c) 2007 Elsevier B.V. All rights reserved.

On the mechanism of void growth and the effect of straining mode in ductile materials

Finite element analysis is employed to investigate void growth embedded in elastic-plastic matrix material. Axisymmetric and plane stress conditions are considered. The simulation of void growth in a unit cell model is carried out over a wide range of triaxial tensile stressing or large plastic straining for various strain hardening materials to study the mechanism of void growth in ductile materials. Triaxial tension and large plastic strain encircling around the void are found to be of most importance for driving void growth. The straining mode of incremental loading which favors the necessary strain concentration around void for its growth can be characterized by the vanishing condition of a parameter called "the third invariant of generalized strain rate". Under this condition, it accentuates the internal strain concentration and the strain energy stored/dissipated within the material layer surrounding the void. Experimental results are cited to justify the effect of this loading parameter. (C) 2000 Elsevier Science Ltd. All rights reserved.

Elimination of loading reverberation in the split hopkinson torsional bar

The loading reverberation is a multiple wave effect on the specimen in the split Hopkinson torsional bar (SHTB). Its existence intensively destroys the microstructure pattern in the tested material and therefore, interferes with the study correlating the deformed microstructure to the macroscopic stress-strain response. This paper discusses the problem of the loading reverberation and its effects on the post-mortem observations in the SHTB experiment. The cause of the loading reverberation is illustrated by a stress wave analysis. The modification of the standard SHTB is introduced, which involves attaching two unloading bars at the two ends of the original main bar system and adopting a new loading head and a couple of specially designed clutches. The clutches are placed between the main bar system and the unloading bars in order to lead the secondary loading wave out of the main bar system and to cut off the connection in a timely manner. The loading head of the standard torsional bar was redesigned by using a tube-type loading device associated with a ratchet system to ensure the exclusion of the reflected wave. Thus, the secondary loading waves were wholly trapped in the two unloading bars. The wave recording results and the contrasting experiments for examining the post-mortem microstructure during shear banding both before and after the modification highly support the effectiveness of the modified version. The modified SHTB realizes a single wave pulse loading process and will become a useful tool for investigating the relation between the deformed microstructure and the macroscopic stress-strain response. It will play an important role especially in the study of the evolution of the microstructure during the shear banding process. (C) 1995 American Institute of Physics.

梯度补偿法控温晶体的高功率绿光激光器

研究了平均功率超过30 W的稳定高效全固态绿光激光器,分析得出影响全固态腔内倍频激光器倍频效率和输出稳定性的主要因素是倍频晶体局部温升造成的相位失配和热透镜效应,采用温度梯度补偿控温法对大尺寸倍频晶体进行温度控制,降低激光器工作中倍频晶体内外温度梯度从而有效地克服因晶体局部温升造成的倍频相位匹配角失配和热透镜效应。采用三条60 W的半导体激光二极管阵列板条侧面抽运Nd:YAG激光增益介质棒,采用声光调Q,平凹直腔和腔内倍频结构配合温度梯度补偿控温法对大尺寸倍频晶体进行温度控制,得到了稳定高效的532 nm

A planar waveguide Nd : YAG laser using active Q-switching of a hybrid unstable resonator

A planar waveguide laser operating in a negative branch unstable resonator is Q-switched by an acoustooptic mod latorin anew configuration, providing effective, high-speed switching. The laser using a 200-mu m Nd:YAG core, face pumped by 10 laser diode bars, has produced 100-W output in a good beam quality at 100-kHz pulse rate, and 4.5 mJ at lower frequency with 15-ns pulse duration.