移去热源前后中高碳钢堆焊温度场和应力场的数值模拟

以中高碳钢60CrMnMo为研究对象,测量了堆焊后的残余应力场.采用有限元分析对热源移去前后堆焊温度场和应力场进行了数值模拟.残余应力场实测结果与模拟结果基本吻合,证明了模型的有效性.温度场模拟获得了不同时刻整个试样的温度分布及试样上各典型截面的温度变化曲线.堆焊16 s后移去热源前后温度场分布有很大差异,堆焊结束后,热量迅速向下表面及周界方向传播.直至180s,试样温度场显现平衡态,传热基本停止,此时温度峰值位于靠近下表面心部,内外温差不大.利用温度场模拟结果模拟了堆焊热源移去前后几个关键时刻的瞬态过程应力.结果表明,应力峰值出现于热影响区与母材区交界面,跃变点前后变化十分显着.     

参数音频编码算法的改进

参数音频编码是一种基于产生音频信号的参数模型的有效编码方法。最近已用于很低码率的音频编码中,如MPEG-4Version2音频标准HILN。这里提出HILN参数音频编码的改进算法。改进算法采用了自适应的基于倒谱的基频检测算法,利用倒谱和频谱特性,保证了大范围内基频提取的效率和准确性。在正弦波合成中采用相位匹配合成算法,保证了帧间参数的连续性。改进算法还对残差信号进行预处理,去除不必要的干扰分量,最大限度重建原音频信号,提高了合成音频信号的质量。     

The phenomenon of anisotropy of the resistance to microcleavage for a carbon steel prestrained in compression

The effect of compressive plastic prestrain on the resistance of carbon steels to microcleavage is investigated using grade 30 steel as an example. Precompression is found to result in the occurrence of anisotropy of the “brittle” strength R_mc of the steel, the essence of which is in its decrease for specimens cut out in the longitudinal direction and increase in the microcleavage resistance for specimens cut out in the transverse one. It is shown that the main cause of this effect are oriented residual stresses. The value of the oriented residual stresses for specimens cut out in the longitudinal and transverse direction is estimated. A strong embrittlement of the steel is observed in the longitudinal direction after compression. The shift in the ductile-brittle transition temperature reaches the maximum value of 168°C. __________ Translated from Problemy Prochnosti, No. 6, pp. 91–102, November–December, 2007.     

Confocal laser scanning microscopy: Applications in material science and technology

Confocal laser scanning microscope (CLSM) has great advantage over a conventional microscope because it rejects the light that does not come from the focal plane, enabling one to perform optical slicing and construction of three-dimensional (3D) images. Further its high axial resolution, sharp image quality and associated quantitative image analysis provide vital structural information in the mesoscopic range for the full 3D realization of the microstructure. Because of this unique feature, CLSM is now finding wider applications in the study of variety of materials and processes such as phase separation in binary polymer mixtures, fracture toughness in alloys, in determining residual strains in fibre-reinforced metal composites, and in microvisualization of corrosion. This paper reviews some of these recent applications and also discusses our results on colloidal dispersions. CLSM has been used to characterize the amorphous structure in highly-charged colloidal systems which have undergone gas-solid transition. CLSM images show presence of large voids deep inside the disordered suspensions. Frame averaged images reveal that the structural disorder is amorphous. The reasons for voids coexisting with dense amorphous regions and their implications on colloidal interactions are discussed. The article also reviews the use of fluorescence-CLSM in the investigation of novel materials of technological importance such as template-directed colloidal crystals with preferred orientations and multilayered structures with different crystal plane symmetries. Direct measurement of the interfacial curvatures for a bicontinuous polymer blend system as well as real space measurement of structure in phase separating polymer mixtures are now possible using CLSM. This paper reviews some of these results highlighting the unique advantages of confocal microscopy for better understanding of the microstructure and mechanistic aspects of various important phenomena in a large variety of materials.     

水驱油田剩余油的测井技术

油田注水开采能够增加原油产量和提高采收率。世界许多油田都是采用注水开采石油,我国水驱油田占87%。测井技术是探测水驱油田剩余油饱和度的重要方法和有效手段。本文论述水驱油田剩余油的测井技术现状和发展趋势。     

An evaluation of failure criteria for matrix induced failure in composite materials

This paper reports on work being undertaken in the Cooperative Research Centre for Advanced Composite Structures Ltd. (CRC-ACS) to develop improved techniques for predicting the failure of composite materials. The procedures being investigated include a maximum strain criterion for fibre failure. For failure of the resin a new approach, which includes determination of the residual stresses due to manufacturing, is being trialed. This work closely parallels the new criteria proposed by Gosse and Hart-Smith [AIAA/CRC-ACS text on composite materials, submitted for publication] and we have subsequently replaced a simple stress criterion for matrix failure with their proposals based on strain invariants. The new procedures are applied to the failure of laminates in bolted joints with complex steered fibre patterns. Thermal residual stress was included to predict the matrix failure of T-section laminates under loads that open the angle between the flanges and the web. Here a transverse tension stress criterion was used.     

残铝对35CrNiMoV钢晶粒度的影响

研究了残余铝含量对35CrNiMoV钢晶粒度及其晶粒长大倾向的影响,并探讨了相关机理.     

纤维铝合金胶接层板残余应力分布

本文采用准三维有限元方法,计算对称铺设混杂复合层板在固化时产生的残余应力,给出了芳纶纤维/树脂-铝合金层板,在自由状态和施加预应力情况下的残余应力计算值,以及不同温度变化下残余应力计算值。本文还给出铝合金-玻璃纤维/树脂-芳纶纤维/树脂层板,在自由状态下固化时的残余应力值。某些计算结果与应变片包埋法实验测得的层板残余应力值十分吻合,表明了计算方法的正确性。用准三维有限元分析残余应力的方法,为设计和制造出满足最佳力学性能要求的层板提供了有价值的参考。     

Failure analysis of brass bolt from mausoleum

Brass is usually considered to be a good candidate material for use in a nonaggressive corrosion environment. Brass 260 was used in a rural environment (at a mausoleum) as fixturing hardware that holds etched marble slabs that cover the interment region. After 12 years of service, the bolts began breaking, and the marble slabs crashed to the ground. Failure analysis investigation showed that “seasonal cracking” occurred due to interaction of the bolt with moisture and fertilizer. The company that designed the mausoleum hardware believed that the bolt manufacturer was at fault. However, the only specification given to the bolt manufacturer indicated alloy and dimensions. The bolts were replaced at considerable cost, proving once again that even a seemingly simple component can prove to be costly if not designed by the proper engineer.     

白酒发酵糟醅中残余酒精含量检测方法的探讨

研究了重铬酸钾比色法检测浓香型白酒发酵糟醅中残余酒精含量的最佳测定条件。结果表明：发酵糟醅经过蒸馏，以重铬酸钾的硫酸溶液作参比，馏出液、重铬酸钾和浓硫酸的用量比为2：1：4时，在600nm处测定，不仅重铬酸钾的还原产物有最大吸收值，而且能最大限度地避开发酵糟醅中干扰物质对吸光度的影响。