CHARACTERIZATION OF POWDER FLOWABILITY USING MEASUREMENT OF ANGLE OF REPOSE

In response to the need in industry for a quick and reproducible method of measuring the flowability of powders in processes involving transport and storage, the apparently simple idea of measuring angle of repose has been revived. The simple tester first used has evolved over a number of years into the present version which is shown to be capable of handling quite small samples of powders that are even slightly cohesive. Experimental data are presented and results shown to compare consistently with the better known Hausner ratio.     

用裂纹张开位移计算三点弯曲试样的动态应力强度因子

给出了一种由裂纹的动态张开位移计算三点弯曲试样的动态应力强度因子的简单方法。对于两种不同几何尺寸的试样,在三类不同载荷作用下给出了数植算例,并与完全的动态有限元方法的计算结果进行了比较。结果表明:两种方法的计算结果相当一致。最后,还给出了由测定三点弯曲试样的裂纹张开位移确定试样的动态应力强度因子,最终确定材料动态起裂韧性的方法。     

Constitutive equations for metal powders: application to powder forming processes

A new constitutive model for cold compaction of metal powders is developed. The plastic flow of metal powders at the macroscopic level is assumed to be representable as a combination of a distortion mechanism, and a consolidation mechanism. For the distortion mechanism the model employs a pressure-sensitive, Mohr–Coulomb type yield condition, and a new physically based non-associated flow rule. For the consolidation mechanism the model employs a smooth yield function which has a quarter-elliptical shape in the mean-normal pressure and the equivalent shear stress plane, together with an associated flow rule. The constitutive model has been implemented in a finite element program. The material parameters in the constitutive model have been calibrated for MH-100 iron powder by fitting the model to reproduce data from true triaxial compression experiments, torsion ring-shear experiments, and simple compression experiments. The predictive capability of the constitutive model and computational procedure is checked by simulating two simple powder forming processes: (i) a uniaxial strain compression of a cylindrical sample, and (ii) forming of a conical shaped-charge liner. In both cases the predicted load–displacement curves and density variations in the compacted specimens are shown to compare well with corresponding experimental measurements.     

MICROSTRUCTURE AND CHARACTERISTICS OF MECHANICALLY ACTIVATED W-Cu POWDER

Introduction Tungsten-copper alloy powders are used in many fields on account of the high electric and thermal conductivities of copper and high melting point of tungsten. W-Cu pow-ders, as prepared conventionally by means of infiltration, has the disadvantage of inhomogeneity in microstructure, and are difficult to work with after sintering. Increasing the particle activity of these powders tends to accelerate the sintering process, lower the sintering temperature and improve their properties…     

圆盘离心沉降法测定固体粉末的粒度分布

本文报道用圆盘离心沉降法对几种粉末样品的粒径大小及粒度分布测定的结果,并且讨论了颗粒形状、消光系数和粉末分散状态等因素的影响。试验结果表明,在给定的条件下,利用LKY-1型微粒测定仪对粉末粒度测定的重复性好,尤其适用于测定微细粉末的粒度分布;当石墨或MoS_2粉末样品的浓度为0.5％时,选用4％鞣酸作分散剂的效果最好。作者认为,固然光密度与微粒的消光系数有关,但对于黑灰色的粉末样品而言,因其产生的光学效应非常微弱,故可近似地把消光系数视为常数而忽略它的影响。     

METHODS FOR DUSTINESS ESTIMATION OF INDUSTRIAL POWDERS

Handling industrial powders leads to dust emissions. These emissions tend to generate human diseases or cause other environmental effects. A multitude of apparatus has been developed to estimate this dustiness behaviour of powders. Two of these well-known methods are presented and compared with each other. A third recently developed method is also introduced.     

用振动梁方法测量粘弹性材料的复模量和粘弹性参数

本文利用共振梁方法,通过对一点响应、相位滞后和共振频率的测量,可以获得粘弹性材料的复模量以及标准线性固体模型的三个参数,即松弛模量、松弛系数和蠕变系数.实验结果表明,实验原理正确,测试系统可靠而且简单实用.     

用光电技术测定爆轰参数

本文介绍了一种用光电技术同时测定爆速和爆温、爆压和爆温的方法。用光电比色技术测定炸药爆轰温度的同时,用两个爆轰面上爆轰的时间差计算爆轰波速度;或用透明介质中冲击波速度来反算炸药中的爆轰压力。方法原理可靠,技术简便。     

3D打印石膏试件力学性质实验

3D打印技术目前已广泛应用在医疗、航空、汽车、建筑等领域,文中做了3D打印技术在岩石力学领域的应用尝试.利用3D打印技术制作两种类型的石膏试件进行实验室单轴压缩试验.实验表明:3D打印技术可以快速、精确、灵活地制作出所需复杂尺寸的试件;打印石膏试件密度较低;3D打印石膏试件具有强度低和塑性强的特性;简单标准试件的力学性质具有可重复性,含裂纹试件力学性质差异较大;含裂纹试件的制作尚存在技术上的困难.     

氢氧混合物爆燃转变为爆轰的时间测量

本文用自制的红外探测仪,测量了氢氧混合物在爆炸激波管中经电火花点火后,由爆燃转变为爆轰(DDT)的时间。为研究可燃物的爆炸特性提供了一种简易的测量方法。     

利用水下爆炸法评价火炸药爆炸危险性的研究

本文提供了一种测定火炸药冲击感度,并根据测定值判定其冲击爆炸危险性的新方法测定水下爆炸气泡能法。通过对30几种炸药的试用,判定的结果与文献报道的用其他方法判定的结果相当好的一致。而且本法的优点还在于同时可得到试样的动、静态威力,操作简便、安全、噪音小。此外,利用本试验法还探讨了炸药形态、惰性介质(水)对冲击感度的影响。这些对于处理炸药时应如何采取安全对策具有指导意义。     

自动消除载荷偏心影响的引伸计研究

本文基于拉伸圆截面试样圆周上各点的应变分析，提出一种自动消除载荷偏心影响的引伸计。该引伸计结构简单、可靠、使用方便。特别是在测定金属杨氏模量中更为适用。用电测实验对比校核的数据表明，自动消除载荷偏心影响引伸计安装在不同位置上测量的相对误差不超过０．５％。     

The diffractographic strain gage

A method for measuring strain using diffraction of light from a single aperture is described, and results of a comparison tensile test with an electrical-resistance strain gage are presented. The “diffractographic strain gage” is shown to have high sensitivity, linearity, accuracy and temperature compensation and the ability to operate in a variety of hostile environments. It is furthermore simple, inexpensive, and the data can be collected by eye without assistance from further instrumentation.     

用三线摆测定物体对非质心轴的转动惯量

对三线摆的线性近似模型和转动惯量计算公式的由来作了简要说明. 分析了三线摆扭振系统 质心偏移对转动惯量测试的影响，给出了扭振系统质心与三线摆中心轴对齐的判别准则和用 三线摆测定物体对非质心轴转动惯量的工程实用方法. 通过工程实例说明了该方法的有效性 与可靠性. 最后讨论了提高转动惯量实测精度的几项具体措施.     

激光定向能量沉积的粉末尺度多物理场数值模拟

激光定向能量沉积技术作为一种同轴送粉式金属增材制造技术, 以其制造效率高、成形尺寸大等优势在航空、航天、交通等领域具有广阔的应用前景. 然而, 该技术在金属零件的尺寸精度和形状精度控制方面存在诸如尺寸偏差大、表面不平整等控形问题, 亟需发展高效高精度预测熔覆层成形尺寸形貌的数值模拟方法. 针对该问题, 本文建立了考虑激光-粉末-熔池交互过程的高保真多物理场数值模型. 其中, 采用高斯面热源等效激光光束, 利用拉格朗日质点法求解粉末输送及其与激光交互的过程, 进一步结合有限体积法和流体体积法求解粉末-熔池的交互及其流动凝固过程, 并通过TC17合金单道熔覆层实验结果进行了验证. 基于该模型, 首先预测了不同工艺参数下单道熔覆层形貌尺寸, 并对熔覆层形貌的变化趋势及其内在的物理机理进行了深入分析. 结果表明, 依赖于工艺参数的粉末温度分布和粉末基板能量分配比例对熔池流场和熔覆层尺寸有显著的影响. 本文所建立的数值模型可辅助激光定向能量沉积增材制造技术控形工艺参数优化, 所得结论可为成形件尺寸和形状精度控制提供理论指导.      

Moiré-fringe multiplication by means of filtering and a wave-front reconstruction process

Two principal problems associated with the practical application of moiré fringes are to obtain sufficient sensitivity for measuring small strains and to develop a simple and inexpensive technique for engraving lines on the surface of a model. This paper deals with simple solutions to both problems. It is shown that the maximum number of fringes that can be observed for a given model is independent of the gratings utilized and depend only on the geometry of the employed optical system. Examples of moiré patterns corresponding to the equivalent of 6000 lines per inch and patterns of the derivatives of the displacements corresponding to the same number of lines illustrate the paper.     

高速三维边界层的横流不稳定性

用两点四阶差分格式研究旋转圆锥超音速三维边界层的横流不稳定性和壁面冷却对稳定性的影响数值结果表明，与二维边界层相比横流使三维边界层第一模式增长率增大，对第二模式影响很小；Ｍｅ＜４３第一模式最不稳定，Ｍｅ＞４３第二模式最不稳定；三维边界层最不稳定第二模式是三维波，二维边界层则为二维波；壁面冷却对第一模式起稳定作用，对第二模式起不稳定作用     

A new method for measuring impulsive force at contact parts

A simple method has been devised for measuring the impulsive force generated at a contact part. Special sensing plates are used to produce an effect equivalent to the embedment of small strain gages in a solid. This method is effective for measuring the impulsive force directly and sensitively, it is almost entirely free from the disturbance caused by interference with reflected waves. It is even effective for the case in which an elastic-plastic deformation may occur at the contact part and the contact area may vary with time.     

PREPARATION AND PROPERTIES OF ULTRAFINE COMPOSITE POWDERS OF Fe_3O_4 AND Ni/MICA

This paper presents the preparation of ultrafine powders of Fe3O4 and Ni by a chemical method, followed by mixing the prepared powders with mica and other ultrafine powders for synthesizing microwave absorption coatings. The microwave attenuation rate of the coatings was measured by the Microwave Network Analyzer in the frequency range of 8-12 GHz at room temperature. The results indicate that microwave could be absorbed by the coatings with an effectiveness strongly dependent on the powder sort and content and the coating thickness.     

物理老化对玻璃态高聚物非线性蠕变行为的影响

在不同应力水平下对经历不同老化时间的有机玻璃(PMMA)进行常温蠕变测试,分析物理老化和应力对材料蠕变柔量函数的影响.分析表明,老化时间对PMMA蠕变行为的影响满足流变简单性规律,即不同老化时间的蠕变柔量曲线可以沿对数时间轴平移而叠加到参考曲线上.取最长的老化时间为参考状态,依时间-老化时间等效原理,得到了各应力水平下的蠕变柔量主曲线.老化移位因子与老化时间在双对数坐标图上呈现线性关系,其负斜率就是老化移位率.结果表明,老化移位率随应力的增高而减小.