Measurements of Forces and Temperature Fields in High-Speed Machining of 6061-T6 Aluminum Alloy

This study focuses on experimental modeling of dry high-speed machining at 30 m/s cutting velocity using 6061-T6 aluminum alloy. A modified Hopkinson bar apparatus is employed to simulate orthogonal machining, a focused array of mercury–cadmium–tellurium infrared detectors is used to measure the temperature distribution around the tool tip, and a three-component quartz force transducer is utilized in measuring the cutting and feed forces. The resulting measurements confirm the assumption of steady-state cutting and allow for estimation of the partition of cutting work into heating, shear, and momentum changes in the chip. In an earlier study, measurements of temperature distributions showed little heating of the finished surface. Therefore, a study of the temperature fields generated during machining with a cutting tool that has a wear-land was performed. The wear-land contributes significantly to the heating of the workpiece and, at this speed, is the most likely mechanism for the generation of residual stresses and a temperature rise on the finished surface.     

A technique for rapid two-stage dynamic tensile loading of polymers

A method for rapid two-stage dynamic-dynamic tensile loading of polymers, based on a tensile Hopkinson bar apparatus, is established. In this technique, the initial incident wave and its reflection are used to load a specimen in quick succession. Consequently, the specimen is stressed, momentarily unloaded, then reloaded until fracture. By adopting appropriate assumptions, a procedure to obtain the associated stress-strain curves for such double-stage loading is formulated. These assumptions are examined experimentally and analytically to substantiate their validity. To verify the proposed approach, a relatively rate-insensitive material, LEXAN 141 polycarbonate, was subjected to two-stage dynamic tension. The stress-strain curves obtained via the procedure established were compared with results from static loading. Favorable correlation between the two indicates that the proposed technique can be applied to the study of load history effects on the dynamic behavior of polymeric materials.     

A split Hopkinson pressure bar technique to determine compressive stress-strain data for rock materials

This paper presents a split Hopkinson pressure bar technique to obtain compressive stress-strain data for rock materials. This technique modifies the conventional split Hopkinson bar apparatus by placing a thin copper disk on the impact surface of the incident bar. When the striker bar impacts the copper disk, a nondispersive ramp pulse propagates in the incident bar and produces a nearly constant strain rate in a rock sample. Data from experiments with limestone show that the samples are in dynamic stress equilibrium and have constant strain rates over most of the test durations. In addition, the ramp pulse durations can be controlled such that samples are unloaded just prior to failure. Thus, intact samples that experience strains beyond the elastic region and postpeak stresses can be retrieved for microstructural evaluations. The paper also presents analytical models that predict the time durations for sample equilibrium and constant strain rate. Model predictions are in good agreement with measurements.     

温度对高应变率扭-拉复合加载下形状记忆合金本构关系影响的研究

利用分离式扭-拉复合加载Hopkinson杆装置,在20℃和500℃下研究了温度对高应变率扭-拉复合加载下铁基形状记忆合金本构的影响,试验结果表明：该材料在高应变率扭-拉复合加载下的名义剪切屈服强度、剪切强度极限和名义拉伸屈服极限、拉伸强度极限均随温度的升高而降低,拉伸和扭转之间具有相互藕合作用。     

弹性压应力波下直杆动力失稳的机理的判据

基于应力波理论和失稳瞬间能量的转换和守恒,导出了一个直杆动力分岔失稳的准则：（1）直杆在发生分岔失稳的瞬间所释放出的压缩变形能等于屈曲所需变形能与屈曲动能之和;（2）在上述能量转换过程中,能量对时间的变化率服从守恒定律。应用临界条件（1）推导出的直杆动力失稳的控制方程和杆端边界条件以及连续条件,与应用哈密顿原理推导的结果完全相同,但不足以构成求解直杆动力失稳问题的完备定解条件,导出包含两个特征参数的一对特征方程。从而建立了求解直杆动力失稳模态和两个特征参数（临界力参数和失稳惯性项指数参数即动力特征参数）的较严密理论方法。     

溶胶-凝胶-硫化法制备硅橡胶吸附萃取搅拌棒

采用溶胶-凝胶-硫化法,以甲基乙烯基硅橡胶和乙烯基封端硅橡胶为原料制备了厚壁硅橡胶吸附萃取搅拌棒(stir bar for sorptive extraction,SBSE)。采用分段硫化和多阶程序升温老化防止涂层脱落和龟裂,一次涂渍涂层厚度约150~250μm,280℃下无流失,使用寿命可达150次。利用所制备涂层,结合自制热解析系统(thermal desorption system,TDS),建立了SBSE-TDS-CGC-FID测定水样中6种多环芳烃(polyaromatichydrocarbons,PAHs)的方法。方法的线性范围为0.3~1000μg/L,检出限为0.002~0.011μg/L,相对标准偏差在0.92%~6.14%之间。该方法能够满足欧盟2005/69/EC指令对多环芳烃低于10 mg/kg的检测要求。     

New integral LEM formulae applied to the nonlinear bar

The linear equivalence method (LEM), introduced by [Bull. Math. Soc. Sci. Math. de la Roumanie 24 (72) (1980) 4417; An. Univ. Bucure ti, ser. Matematica 31 (1982) 75] to get solutions of nonlinear ODEs, was used so far to get differential type representations. New LEM representations of integral type are presented here and used for the study of the nonlinear elastic bar; a good approximating formula for the rotation of the cross-section at the bar end is also obtained, in case of a simply supported bar. A parallel old–new results is made by means of a programming code.     

压弯杆件的动荷性能分析

研究了在轴向动力荷载作用下压弯构件的动力特征，根据压弯构件的动力平衡方程，导出了不同横向荷载形式下的振幅计算公式，分析了横向荷载对杆件动力性能的影响，根据理论研究成果提出了在实际工程中减小杆件振幅的一些措施．     

基于联系数的钢筋抗拉强度测量不确定度评定新方法

钢筋抗拉强度的不确定度包括:钢筋直径的不确定度分量,拉力的不确定度分量,检测结果重复性引入的不确定度分量,数据修约的不确定度分量等等,因此,测量不确定度是与测量数据相联系的,联系数是处理不确定性问题的一种系统数学理论,可以用联系数来表示测量不确定度,为此,提出一种基于联系数的钢筋抗拉强度测量不确定度评定的新方法.     

SINGULARITIES OF SPHERICAL FOUR-BAR MOTION

The |ink curve of a sphericel four-bar mechanism can be separated into two branches.The condition that the double points of the curve must satisfy is given. The double points maybe the double points of either branch, or the intersection points of the two branches.