A micromechanical model for transformation plasticity in steels

Transformation plasticity is the irreversible deformation behaviour of transforming specimens even under a loadstress-state with an equivalent stress significantly lower than the yield stress. This effect is caused by the plastic adaption of the transformation induced volume and shape change of microregions being parts of a grain. Since the corresponding microstress states must be in global equilibrium with the load stress state a semianalytical relation between the global deformations, the load stress state and transformation parameters can be given under the assumption of the same final strain tensor in each micro-region. Especially the influence of the shape change and comparison with experimental data are presented.     

Methods for determining operation life and reactivity depletion for space reactors with fast energy spectra

Space reactors with fast neutron energy spectrums are preferred for their compactness and high fission power density, but require a high fissile inventory. The operation life estimates of these reactors are important to mission planning. This paper examines a number of fuel depletion and neutronics code packages for determining the operation lives of two space reactors with hard fast neutron energy spectra. These are: the lithium-cooled, Sectored, Compact Reactor (SCoRe-S₁₁), and the submersion subcritical safe space (S^4) reactor, cooled with a He–Xe binary gas mixture (40 g/mol). This work investigated the code packages of Monteburns 2.0, MCNPX 2.6C and TRITON and validated their prediction with fuel depletion data for a PWR fuel bundle, with satisfactory results. The operation life predictions of the two space reactors using these code packages are compared with those calculated using a simplified method that couples MCNP5 to a burnup analysis model using the Simulink^® platform. This method considers only the 10 most probable low-Z and high-Z elements of the fission yield peaks plus ¹⁴⁹Sm, and neglects the depletion of fission products due to capture and radioactive decay. The simplified method requires significantly shorter running time and its predictions of the operation lives for the two space reactors are within 0.29–12.5% of those obtained using Monteburns 2.0 and MCNPX 2.6C code packages. This method, however, is not recommended for operation life predictions for space or commercial reactors with thermal neutron spectrums.     

Reactivity control options of space nuclear reactors

This paper compares two ex-core control options of the gas-cooled Submersion Subcritical Safe Space (S^4) reactor with a fast neutrons energy spectrum: (a) rotating BeO drums with 120° thin segments of enriched B₄C in the BeO radial reflector; and (b) sliding segments in the BeO radial reflector. Investigated are the effects on the beginning-of-life (BOL) excess reactivity, reactivity depletion rate and operation life, and the spatial neutron flux distributions and fission power profiles in the core. Also investigated is the effect of reducing the thickness of the enriched B₄C segments in the control drums on the BOL excess reactivity, when one or two of the 6 drums are stuck in the shutdown position. Reducing the thickness of the B₄C segments from 0.5 mm to 0.238 mm, with one drums stuck in the shutdown position, increases BOL cold and hot-clean excess reactivity from +$1.71 and +$0.47 to +$2.38 and +$0.89, respectively. These reactivity values are almost identical to those of the reactor with one of the six reflector segments stuck open in the shutdown position. Results also showed that the control options made little difference in the reactor performance. The power peaking in the reactor core with sliding reflector segments is slightly lower and the spatial power profiles are relatively flatter. The operation life of the reactor with a sliding reflector segments control, when operating at a nominal thermal power of 471 kW, is only 22 full power days longer than with rotating drums control.     

N18锆合金的低周疲劳行为

在不同试验温度（室温～500℃）下,对N18合金进行了低周疲劳试验。试验结果表明：室温～300℃温区,合金表现为明显的循环软化;400、450℃时,合金逐渐呈现循环硬化,450℃时其硬化现象更为明显;500℃时则主要表现为循环饱和。随着温度的升高,疲劳寿命先增加后降低,300℃时疲劳寿命最高。低应变幅下,温度对疲劳寿命的影响更明显。通过疲劳断口SEM分析,室温下疲劳起源于单个裂纹源,疲劳裂纹扩展阶段的微观特征主要是疲劳条纹,局部区域出现轮胎状花样。在高温下为多裂纹源,大量二次裂纹的存在是高温疲劳断口的主要特征。     

铝离子注入不锈钢/铝钎焊接头界面结构研究

采用铝离子注入不锈钢前处理的方法优化了不锈钢/铝钎焊接头质量,研究了钎焊参数对不锈钢/铝钎焊接头形貌及相结构的影响。结果表明,铝离子注入不锈钢前处理的方法可以使后期钎焊获得更好的不锈钢/铝钎焊接头及焊趾形貌;随着钎焊温度的增高、钎焊时间的延长,不锈钢/铝钎焊接头界面脆性相厚度增大。注铝不锈钢/铝钎焊接头断裂形式与界面脆性相厚度密切相关,接头脆性相厚度小于10μm时,不锈钢侧断口处Al相含量很高,接头在钎料区失效,失效形式为韧性断裂;而脆性相厚度大于10μm时,不锈钢侧断口处Fe13Al4、FeAl2等脆性铁-铝相含量很高,接头断裂在脆性相区,接头失效形式为脆性断裂。     

氢气爆炸超压冲击波的工程估算方法简述

超压冲击波是氢气爆炸时产生的主要危害之一,也是导致建筑与人员伤亡的主要因素。文章介绍使用TNT当量估算爆源能量后,计算氢气爆炸产生的超压冲击波几种常用方法,主要包括比例定律法、经验公式法与软件模拟。     

Reduction of dust deposition in air-cooled condensers in thermal power plants by Ni–P-based coatings

Clean Technologies and Environmental Policy - One of the largest problems with most current thermal power plants is the cooling efficiency. This paper aims to massively reduce fuel consumption and...     

三门核电循环水泵房超深基坑支护设计实例

三门核电循环水泵房基坑为超深基坑（最深处为32．3m）,处于基岩面埋藏较浅且上部覆盖较厚淤泥层和回填石层的特殊区域。本工程依据地层条件,将基坑边坡划分为完全基岩边坡、基岩埋深浅且无淤泥地层的边坡、基岩埋深较大且有较厚淤泥层的边坡3种类型。分别采用3种支护型式：放坡、排桩＋岩锚、排桩＋深搅重力墙＋岩锚,有效解决了滨海软土区的地下水位高,淤泥质软土黏聚力及内摩擦角小,基坑侧壁受水平荷载大、易失稳等难题。典型断面计算结果表明,锚拉力最大为361．84kN;基坑侧壁最大水平位移为19．26mm,支护桩最大正负弯矩值为711．36kN·m和-787．52kN·m,基坑顶部最大沉降量为50mm,均满足设计与规范要求。     

Microstructural characteristics and mechanical behavior of B4Cp/6061Al composites synthesized at different hot-pressing temperatures

B₄Cp/6061Al composites have become important structural and functional materials and can be fabricated by powder metallurgy and subsequent hot rolling. In this work, the effects of the hot-pressing temperature on microstructures and mechanical behaviors of the B₄Cp/6061Al composites were investigated. The results showed that compared with the T4 heat treated B₄Cp/6061Al composite hot pressed at 560 °C, the yield strength and failure strain of the composites hot pressed at 580 °C were increased to 235 MPa and 18.4%, respectively. This was associated with the interface bonding strength between the B₄C particles and the matrix. However, the reaction products, identified to be MgAl₂O₄ phases, were detected in the composites hot pressed at 600 °C. The formation of the MgAl₂O₄ phases resulted in the Mg depletion, thus reducing the yield strength to 203.5 MPa after the T4 heat treatment due to the effect of the solid solution strengthening being weakened. In addition, the variation of hardness and electrical conductivity was mainly related to the Mg content in the matrix. Based on the as-rolled microstructures observed by SEM, SR-μCT and fracture surfaces, the deformation schematic diagram was depicted to reflect the tensile deformation process of the composites.     

3-Dimensional numerical optimization of silicon-based high performance parallel microchannel heat sink with liquid flow

A full 3-dimensional (3D) conjugate heat transfer model has been developed to simulate the heat transfer performance of silicon-based, parallel microchannel heat sinks. A semi-normalized 3-dimensional heat transfer model has been developed, validated and used to optimize the geometric structure of these types of microheat sinks. Under a constant pumping power of 0.05 W for a water-cooled microheat sink, the optimized geometric parameters of the structure as determined by the model were a pitch of 100 μm, a channel width of 60 μm and a channel depth of about 700 μm. The thermal resistance of this optimized microheat sink was calculated for different pumping powers based on the full 3D conjugate heat transfer model and compared with the initial experimental results obtained by Tuckerman and Pease in 1981. This comparison indicated that for a given pumping poser, the overall cooling capacity could be enhanced by more than 20% using the optimized spacing and channel dimensions. The overall thermal resistance was 0.068 °C/W for a pumping power of 2 W.