4Cr5MoSiV1热作模具钢锻造加热工艺的改进

攀长钢生产的4Cr5MoSiV1热作模具钢锻材存在超声波探伤合格率较低的问题。分析认为主要原因是沿用较低的锻前加热温度，钢锭加热程度不足造成锻造时大锻材中心没有充分锻透。笔者对4Cr5MoSiV1钢锻造加热工艺进行了递进式改进，逐步调整钢锭加热制度从1180℃最终提高到1270℃．1290℃，同时相应调整退火工艺制度，基本解决了上述问题，探伤废品大幅降低，锻造火次也明显减少，并避免高温加热引起的粗晶降低钢材使用性能，取得了显著的工艺改进效果。另外，采用高温加热也使钢中的显微偏析明显减轻，获得了部分的均匀化扩散退火的效果：一次碳化物减少，尺寸变小，没有尖锐的棱角，冲击韧性比工艺改进前有明显提高。     

喷射沉积柱坯的生长模型

根据现有喷射沉积设备的喷射几何关系推导了柱状沉积坯生长的数学模型,并利用该模型对沉积器的临界下降速度进行了初步估算。     

西藏自治区藏中电网光纤通信网的建设及发展

西藏自治区由于受地理环境等多方面因素的制约，长期以来各地区级的电网均独立运行，造成通信网发展相对滞后。但近几年随着电业大发展，地区电网相互连接共同进行，促进了通信网的快速发展。文章详细介绍了藏中电网光纤通信网的发展现状，包括网络拓扑结构、SDH和PCM设备、光纤线路的建设情况以及现存的问题，并阐述了今后的发展规划。     

Nonlinear seismic response analysis of reinforced concrete tube in tube structure

Super-highly reinforced concrete tube in tube structure is a developing structure system of high-rise building. The more reasonable derivation process of the multi-vertical-line-element model stiffness matrix is given.On the premise of pointing out the problems of present multi-spring element model, combined with present multivertical-line-element model for analyzing on shear wall, the model is expanded to spatial one, and the stiffness matrix of which is derived. Combined with hysteretic axial model and hysteretic shear model, it is suitable for columns,wall limbs and beams with all kinds of section form. Some examples are calculated and compared with test results,which shows that the models have relatively good accuracy. On the base of the experimental phenomenon and failure mechanism for tube in tube structure specimen, nonlinear seismic responses analysis program on the basis of the advantaged element model for tube in tube structure is developed. Calculation results are in good agreement with those of the pseudo-dynamic tests and the failure mechanism can be well reflected.     

陶瓷基复合材料伪半固态触变成形及其在卫星角框件中的应用

提出了陶瓷基复合材料伪半固态成形工艺,并应用该工艺制备了30%(体积分数)Alp/SiCp复合材料卫星角框件.通过金相分析、拉伸等实验方法验证该工艺的可行性.结果表明,该工艺成形的零件微观组织比较均匀;硬度较高,HV可达到6.43GPa;应变(ε)约为0.5%;抗拉强度(σt)约为300MPa.     

Magnetic Perovskite Superlattices Grown by Pulsed Laser Deposition

Magnetic multilayers of (SrRuO₃) _m (SrMnO₃) _n were grown artificially using the pulsed laser deposition technique on (001)-oriented SrTiO₃ substrates. The temperature and magnetic field dependent reisistivity of the superlattices consisting of ferromagnetic (FM) SrRuO₃ and antiferromagnetic (AFM) SrMnO₃ are studied as a function of the SrRuO₃ unit cells. We observed a pinned/biased moment instead of the biased field in the superlattices and we redefine the structure as AFM/FM(Pin)/FM(Free)/FM(Pin) units below a critical field.     

Calibration of the Weibull stress scale parameter, σu, using the Master Curve

This work proposes that the Weibull stress scale parameter, σ_u, increases with temperature to reflect the increasing microscale toughness of ferritic steels caused by local events that include plastic shielding of microcracks, microcrack blunting, and microcrack arrest. The Weibull modulus, m, then characterizes the temperature invariant, random distribution of microcrack sizes in the material. Direct calibration of σ_u values at temperatures over the DBT region requires extensive sets of fracture toughness values. A more practical approach developed here utilizes the so-called Master Curve standardized in ASTM Test Method E1921-02 to provide the needed temperature vs. toughness dependence for a material using a minimum number of fracture tests conducted at one temperature. The calibration procedure then selects σ_u values that force the Weibull stress model to predict the Master Curve temperature dependence of K_Jc values for the material. At temperatures in mid-to-upper transition, the process becomes more complex as fracture test specimens undergo gradual constraint loss and the idealized conditions of high-constraint, small-scale yielding assumed in E1921-02 gradually degenerate. The paper develops the σ_u calibration process to incorporate these effects in addition to consideration of threshold toughness effects and the testing of fracture specimens with varying crack-front lengths. Initial illustrations of the calibration process for simpler conditions, i.e. 1T crack-front lengths, use the temperature dependent flow properties and a range of toughness levels for an A533B pressure vessel steel. Then using the extensive fracture toughness data sets for an A508 pressure vessel steel generated recently by Faleskog et al. [Engng. Fract. Mech., in press], the paper concludes with calibrations of both m and σ_u over the DBT region and assessments of the Master Curve calibration approach developed here.     

浅谈大学英语学习中的误区及对策

本文作者从六个方面总结并分析了大学英语学习中存在的误区,指出英语学习是一个循序渐进的过程.需要大量听、说、读、写的反复训练及文化背景知识的学习积累,以期给学习者一些启示.