A New Model Developed to Evaluate the Contact Area Arising During Nano-indentation Tests With Pileup Behavior of Metal Materials

A new mechanical model is developed in this paper for metal materials to investigate the behavior arising during the loading/unloading process of an indentation test. Two governing differential equations are derived for the depth solution of the indenter tip and the depth solution formed at the separation point, expressed in a power form. All spring/block and damping coefficients shown in these governing differential equations associated with the elastic/plastic and viscous behaviors are determined by the real-coded genetic algorithm. With the aid of experimental results of the depth at the indenter tip shown at large and small indentation depths, aluminum and steel were used as two examples of soft materials in this paper. The pileup behavior is implicitly included in the evaluation of the contact projected area (A) in the present model. A significant difference in is caused if the pileup is not considered in the model. Under a constant maximum load, the contact area is slightly increased by decreasing the loading/unloading rate.     

评价金属精密冲裁适应性的新方法

简要分析了金属板材冲裁时应力状态对变形过程的影响,介绍了一种用拉伸、扭转、压缩变形评价金属材料精密冲裁适应性的新方法.它一改传统的以断面光亮带相对高度来评判的方法,利用材料在达到破坏之前所允许的变形总量来评价其对精密冲裁工艺的适应性.与传统方法相比,其具有不必制备试验模具等优点,迅速便捷,可靠性高.     

Diametrical Elastic Relaxation During Ejection of Lactose-Cocoa Binary Tablets

This work investigates the diametrical elastic relaxation of a compacted binary powder mixture of lactose and cocoa. It has been observed that the addition of lactose improved the mechanical strength of the binary tablets at the higher compaction stresses used in this study. The tablets having the maximum tensile strengths have relatively low diametrical elastic relaxations, similar to the pure cocoa tablets. Meanwhile, pure lactose tablets displayed increasing diametrical elastic relaxations as the compaction stress increased.     

一种蒙特卡罗方法在测量不确定度评定中的新算法

通过对现有利用蒙特卡罗方法进行不确定度评定过程的分析,指出了目前评定过程中存在理论上的不衔接,并给出了一种全新的利用蒙特卡罗方法进行不确定度评定的算法,弥补了现有方法的缺憾。     

7A85铝合金的热压缩流变行为与显微组织EI北大核心CSCD

采用Gleeble-3500热模拟试验机对铸态7A85铝合金进行高温热压缩实验,研究了7A85铝合金在变形温度为300~450℃、应变速率为0.01~10s^(-1)条件下的流变行为与显微组织。结果表明:流变应力在变形初期迅速升至峰值,随后由于动态回复和动态再结晶有所降低,最后趋于稳态;峰值流变应力随变形温度的降低和应变速率的增加而增大,可用Zener-Hollomon参数描述。采用线性回归方法获得7A85铝合金高温条件下流变应力本构方程,其变形激活能Q为253.68kJ/mol。随着lnZ降低,晶粒沿径向拉长,亚晶长大,位错密度和第二相数量降低。软化机制主要为动态再结晶。     

2519A铝合金热压缩流变行为和显微组织分析

在Gleeble-1500D热模拟仪上进行热压缩实验,研究温度从300℃～450℃、应变速率为0．001～10s^-1时2519A铝合金热压塑行为,并用金相显微镜分析在不同热压缩条件下的组织形貌特征。结果表明,流变应力开始随着应变的增大而增大,出现峰值之后慢慢减小并慢慢趋于平稳。应力峰值随温度的增加而减小,随应变增大而增大,其热变形行为可用包含Zener-Hollomon参数的双弦本构关系来描述,得到平均激活能Q=223．11706kj／mol。合金在0．001s^-1～1s^-1。应变速率条件下软化机制主要为动态回复,而当应变速率上升到10s^-1后,合金微观组织出现局部动态再结晶。     

评价企业营销力的一个新方法

市场的可拓性关系着企业市场营销工作的效率和效果，可拓营销力是企业在市场竞争过程中通过营销活动形成的获得消费者认同的能力。这种认同可能会直接带来销售额、利润，也有可能只是使消费者产生了对企业或者产品、品牌的兴趣，但是一定会为未来的企业销售活动打好良好的商誉基础。企业可拓营销力在企业发展中具有重要作用，文章基于企业营销活动的市场影响力讨论了企业可拓营销力指数，并为其科学评价提供了一个新的方法     

速率转台的角速率不确定度评定方法

利用不确定度的理论来评定速率转台的角速率不确定度。     

数据采集系统动态准确度的一种评价方法

介绍了一种用于评价数据采集系统动态准确度的定义及测试方法，同时评价了其动态条件下的偏置误差、增益误差及模数转换有效位数，最终给出了一种数据采集系统的实际测试评价结果。     

A Method to Evaluate the Second Breakdown Resistance of Power Transistors

A new evaluation method of forward-biased second breakdown resistance in power transistors employing a characteristic variation of current gain is presented. Predictions for second breakdown resistance in power transistor are made by monitoring the changing point of the base current at the collector-base junction under the constant voltage and constant current conditions. This characteristic phenomenon which is related to the variation of the current gain is dependent on the temperature and current density at a localized spot of the transistor. It is concluded that the time delay required to reach the changing point of the base current can be considered as a measure of the second breakdown resistance. The forward-biased second breakdown resistance can be measured without damage or degradation of the sample transistors, if the supplied power is removed before the base current reaches the changing point.     

A New Static and Fatigue Compression Test Method for Composites

Abstract: A new test method to determine the compressive properties of composite materials under both static and fatigue loading was developed. The novel fixture is based on the concept of transmitting the load by a fixed ratio of end‐to‐shear loading. The end‐to‐shear load ratio is kept fixed during the test through a mechanical mechanism, which automatically maintains the gripping pressure. The combined loading method has proven very efficient in static loading and is used in the new fixture which is specially designed for fatigue testing. Optimum gripping (shear loading) and alignment of the test coupon are achieved throughout the fatigue life. The fatigue strength obtained is more reliable because bending of the specimen due to poor gripping and alignment is minimised. The application of the new fixture to static and fatigue compression is demonstrated by using unidirectional carbon/epoxy and glass/polyester composite systems. Repeatable results and acceptable failure modes are obtained under both static and fatigue loading.     

利用水下散射场测量橡胶弹性模量的方法研究

橡胶是减振降噪的主要材料之一,对其材料性能的掌握是进行结构设计的前提,针对中高频率下橡胶材料弹性模量测量标准的空白,提出一种新的测量方法。在自由场条件下,通过测量橡胶球的散射声场,计算散射场的勒让德展开系数,建立反演模型,求解橡胶球的声学参数,再根据材料参数之间的转换关系来获得弹性模量。实验结果表明,所测橡胶球的动态弹性模量在中高频上的变化规律与已知的结论一致,目标的反演散射声场与测量的散射声场符合较好。     

振动时效效果的振动评价

本文通过实验分析,揭示了振动时效前后材料微观组织的变化规律,研究了残余应力松驰与刚度变化间的相互关系,在此基础上,借助振动模态灵敏度分析,建立了一种评价振动时效效果的振动判据。     

Work Required to Cause Failure of Tablets in Diametral Compression

During diametral compression testing load-displacement curves were obtained for tablets made from some direct compression agents, by continually monitoring the force applied to the tablet and the distance moved by the lower compression platten. The area under these curves, termed work of failure, was calculated by numerically integrating the applied force with respect to platten displacement. The resistance to breakage of the tablets was assessed by a semi-empirical multiple diametral impact test in which a tablet was subjected to repeated impact until failure occurred. Work of failure was related to the number of impacts required to cause failure and appears to be a better quantitative assessment of a tablet's mechanical properties than tensile strength.     

TC4钛合金高温压缩变形行为的研究

采用等温压缩试验法,分析了TC4合金在高温低速变形过程中变形温度、应变速率对变形抗力及组织的影响,并通过回归分析得出了该合金高温变形过程中的流变应力方程,为TC4热变形工艺的制定提供参考依据。     

7075铝合金热压缩过程变形行为和载荷研究

采用MMS-300多功能材料试验机对7075铝合金在变形温度300-450℃、应变速率0．01～40s^-1下单道次压缩过程进行了实验研究,并根据其流变曲线对热压缩过程进行了数值模拟,分析了变形速度、温度和摩擦对变形栽荷的影响规律。结果表明：7075铝合金变形过程发生了动态再结晶,应力-应变曲线表现出波浪形,波动周期大致相同,振幅随着应变增加逐渐减小;变形速度较小时,变形速度增加,临界应变增加,变形速度增加到一定程度时临界应变反而降低。随着变形速率增加和变形温度降低,载荷增加,而摩擦对7075铝合金热压缩过程的栽荷影响不大;当变形速率增加到一定值时,载荷值对速度敏感度降低。     

Evaluation of a New Cellulose Material as Binding Agent for Direct Compression of Tablets

The properties of a new microcrystalline cellulose product Emcocel^R, was compared with those of fine grade of other commercial microcrystalline cellulose, Avicel^R PH 101. The crystal structure of Avicel was noticed to be some more amorphous than that of Emcocel. Both materials were similarly composed of irregularly shaped fibrous cellulose particles. The particle size distribution was clearly larger for Emcocel than for Avicel. Emcocel contained more both very small and very large particles. The loose density was also slightly smaller for Emcocel. There was practically no difference in spesific: surface area, water content and effective density of these materials. The behaviour of both microcrystalline cellulose powders during flow and binding processes was similar. Emcocel and Emcocel were rather cohesive and only fairly flowing materials. Tablets with very advantageous strength/pressure profiles were possible to produce using plain materials and also using tablet masses containing high concentrations of acetaminophenone. According to the results of this evaluation the physical and tableting properties of a new microcrystalline cellulose material, Emcocel, resemble very closely those of Avicel PH 101. Thus neither advantage nor disadvantage is derived using Emcocel instead of Avicel PH 101 as a binding component in tablet masses.     

Experimentally Designed Optimization of Direct Compression Tablets

The work reported here describes the improvement of an industrial production of tablets formed by direct compression. This formulation contained 50% active substance of plant origin as a nonhygroscopic powder. The first step was to evaluate a number of direct compression excipients in preformulation tests and then make up a basic formulation providing tablets with correct characteristics. The second step was the optimization of the initial formulation using a two-level factorial experimental design. This enabled the best formulations to be selected objectively.     

Experimentally Designed Optimization of Direct Compression Tablets

Abstract

The work reported here describes the improvement of an industrial production of tablets formed by direct compression. This formulation contained 50% active substance of plant origin as a nonhygroscopic powder. The first step was to evaluate a number of direct compression excipients in preformulation tests and then make up a basic formulation providing tablets with correct characteristics. The second step was the optimization of the initial formulation using a two-level factorial experimental design. This enabled the best formulations to be selected objectively.