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991.
混凝土面板堆石坝坝料开采爆破试验 总被引:5,自引:3,他引:2
介绍在某水电站进行的混凝土面板堆石坝坝料开采爆破试验的情况。试验突破了仅根据岩石坚固性系数选取单位炸药消耗量的传统习惯,结合岩体裂隙与风化程度确定单位炸药消耗量,并采取分段装药,严格控制各段装药量和炮孔堵塞长度等措施,取得了良好的爆破效果。 相似文献
992.
993.
本文分析了给粉机变频器低电压跳闸的原因和解决办法,为解决给粉机变频器低电压跳闸,消除设备隐患提供了经验。 相似文献
994.
Calogero D. Presti Francesco Carrara Giuseppe Palmisano 《Analog Integrated Circuits and Signal Processing》2007,51(1):51-54
A variable-gain up-conversion mixer for 5-GHz WLAN applications is presented, whose input stage is based on a novel variable
gain transconductor. The proposed topology features reduced power consumption by exploiting dc current reuse for mixer biasing.
Moreover, a new low-consumption control circuit is introduced, which achieves a temperature-stable and linear-in-dB characteristic,
providing a 40-dB dynamic range within ±1 dB gain error. 相似文献
995.
996.
997.
998.
Hopkinson bar techniques have played an important role in the study of high-rate deformation and fracture behavior of materials.
In the current work, a split Hopkinson pressure bar was developed for dynamic four-point bend fracture testing, referred to
as a “two-bar (incident and transmitted bars)/four-point” (2-bar/4-pt) bend test. To further understand some fundamental issues
regarding stress wave propagation in this 2-bar/4-pt bend testing system, dynamic fracture tests were performed in pulse-shaped
and unshaped pulse testing conditions. The effect of the pulse shaper on the incident pulse characteristics (rise time and
duration), specimen’s dynamic response (load and loading point displacement), crack initiation time and stress-state equilibrium
were investigated experimentally in the current work. The present results show that stress state equilibrium can be achieved
prior to fracture initiation in notched and precracked specimens. In the pulse-shaped bending test, the specimen is more likely
to attain stress-state equilibrium than in an unshaped incident pulse test. The crack initiation time was extended and the
time required for attaining stress equilibrium was reduced by pulse shaping due to the tailored incident pulse having a longer
rise time, which ensures that stress equilibrium is achieved prior to crack initiation.
This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during
the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals,
Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee. 相似文献
999.
Aluminum casting alloys exhibit creep behavior when the materials are exposed to high temperature and load. In this article,
the stress- and temperature-dependent creep behavior of a die casting A380-T5 aluminum alloy was simulated using a classical
constitutive model. The bolt-load retention behavior of the material was analyzed in a head bolt joint in an aluminum engine
under thermal cycle condition using the finite element method. In this simulation, transient thermal analysis was performed
first to calculate the metal temperature at the head bolt joint as a function of time during engine thermal cycling. This
temperature was then input as the thermal loading in the subsequent structural analysis to calculate its effect on the bolt-load
retention. The finite element analysis (FEA) model for the bolt-load retention simulation includes not only the plasticity
in all metal components but also the creep properties of head bolt threads in the cast aluminum engine block. The FEA model
was validated by good correlation between the predicted head bolt-load loss and the experimental measurement during engine
thermal cycling. The simulation results also indicated that creep in the head bolt threads of cast aluminum engine block was
mainly responsible for the load loss in the head bolt joint.
This article is based on a presentation given in the symposium entitled “Simulation of Aluminum Shape Casting Processing:
From Design to Mechanical Properties” which occurred March 12–16, 2006 during the TMS Annual Meeting in San Antonio, Texas
under the auspices of the Computational Materials Science and Engineering Committee, the Process Modeling, Analysis and Control
Committee, the Solidification Committee, the Mechanical Behavior of Materials Committee, and the Light Metal Division/Aluminum
Committee. 相似文献
1000.
A series of nanocomposite thin films, composed of Nd2Fe14B and α-Fe, has been prepared by DC-magnetron sputtering combined ion beam sputtering onto Si (100) substrates. The effects of post annealing on the microstructure and magnetic properties of [NdFeB/α-Fe/NdFeB]-type thin films have been investigated. The X-ray diffraction (XRD) study showed that annealing of the films for 30min at temperatures 550,600,650,700℃ resulted in the appearance of diffraction peaks, characteristic for Nd2Fe14B tetragonal structure, α-Fe and Nd2O3 phases. The investigation using the Vibrating Sample Magnetometer (VSM) with a maximum applied field of 2 T indicated that with the increase of the annealing temperature, the magnetic properties of the multilayer films were improved and reached peak value at 650℃ (Hci=41.72kA·m-1, Mr/Ms=0.4, (BH)max=30.35kJ·m-3), after which the magnetic properties were decreased greatly. Along with the increase of the thickness of α-Fe layer from Tα-Fe16nm, the coercivity Hci, saturation magnetization Ms, and remanence ratio Mr/Ms all declined. As the Atomic Force Microscope (AFM) indicated, after being annealed at 650℃ for 30min, the sample was showed fine surface morphology with grain size 60nm≤dα-Fe≤80nm and 100nm≤dNdFeB≤150nm. 相似文献