Slip-line modeling of machining with a rounded-edge tool—Part I: new model and theory

The effect of tool edge roundness attracts growing attention from the international machining research community due to ever accelerating applications of precision, super-precision, micro-, and nano-machining technologies in a wide variety of modern industries. A new slip-line model for machining with a rounded-edge tool and its associated hodograph are proposed in this paper. The model consists of 27 slip-line sub-regions, each sub-region having its own physical meaning. It is demonstrated that the model simultaneously takes into account nine effects, such as the shear-zone effect and the size effect, which commonly occur in machining. Eight groups of machining parameters, such as the ploughing (parasitic or non-cutting) force and the chip up-curl radius, can be simultaneously predicted from the model. Furthermore, the model incorporates eight slip-line models previously developed for machining during the last six decades as special cases. An additional special case that involves a parallel-sided shear zone can also be derived from the new model. A mathematical formulation of the model is established based on Dewhurst and Collins's (1973) matrix technique for numerically solving slip-line problems. A purely analytical equation is proposed to predict the thickness of the primary shear zone. This equation is also employed to predict the shear strain-rate in the primary shear zone.     

宾汉姆体的缓凝砂浆在单螺杆挤出机中的流动

在实验的基础上，研究了宾汉姆体的缓凝砂浆在单螺杆挤出机中的流动；运用流变学理论， 建立了缓凝砂浆螺旋输送物理模型；对缓凝砂浆螺旋输送与包裹机构的工作机理进行了分析 与研究，得出了缓凝砂浆连续输送的条件，螺杆转速必须大于临界转速. 实验发现：宾汉姆 体的缓凝砂浆在螺旋输送与包裹机构中当螺杆转速在78$\sim$240\,r/min范 围内可实现连续输送和包裹.     

Beitrag zur Prüfung metallischer Werkstoffe im Torsionsversuch

Zusammenfassung Der Torsionsversuch eignet sich zur Untersuchung des plastischen Verhaltens von Metallen bei erhöhten Temperaturen, wenn die Fließspannung stark von der Umformgeschwindigkeit abhängt. Aus der gemessenen Drehmoment-Drehwinkel-Kurve wird die Fließkurvek _f () berechnet. Hierfür wird ein Fließkriterium benötigt, dessen Unsicherheit im allgemeinen größer ist als alle Meßfehler. Diese Unsicherheit geht aber nicht in die berechnete Dehngeschwindigkeitsempfindlichkeit ein, die somit als Hauptergebnis des Versuches anzusehen ist.Um die Bedingungen technischer Warmumformung zu simulieren, wird die Verwendung extrem kurzer Proben (flacher Scheiben) empfohlen, womit sehr hohe Umformgeschwindigkeiten erreicht werden können. Für die Auswertung derartiger Versuche ist die wirksame Länge der kurzen Proben — experimentell oder semiempirisch — zu bestimmen und die Kerbwirkung zu berücksichtigen. Im Gegensatz zur herkömmlichen Vorgehensweise wird empfohlen, die örtliche Spannung und Verzerrung nicht für die Mantelfläche der Probe zu berechnen, sondern für einen kritischen Radialabstand im Innern der Probe, für den die Schiebung von der Kerbwirkung unabhängig ist, so daß sich die zuverlässigsten Werte ergeben.

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Summary The torsion test is often used for studying the plastic deformation of metals at elevated temperatures when stress depends strongly on the strain rate. From the measured torque-twisting angle curve, the stress-strain curvek _f () has to be calculated. For this purpose a yield criterion has to be used the uncertaintly of which normally exceeds all experimental errors. This uncertaintly, however, does not propagate into the calculated strain rate sensitivity which therefore may be considered as the main result of the torsion test.For simulating the conditions of technical hot forming processes, the use of extremely short test pieces (flat discs) by which very high strain rates can be obtained is recommended. For evaluating the test data the efficient lenght of short specimens has to be determined. In opposition to the conventional procedure of test evaluation, it is recommended not to calculate stress and strain for the surface of the specimen but for a critical radius for which strain is independent of the notch effect so that the most reliable values are obtained.

Mit 5 Abbildungen     

Plastic surface strain mapping of bent sheets by image correlation

A technique using a single CCD camera, a precision rotation/translation stage, a telecentric zoom lens, and digital image correlation software is described for measuring surface profiles and surface plastic strain distributions of a bent thin sheet. The measurement principles, based on both parallel and pinhole perspective projections, are outlined and the relevant mathematical equations for computing the profiles and displacement fields on a curved surface are presented. The typical optical setup as well as the experimental measurement and digital image correlation analysis procedure are described. The maximum errors in the in-plane and out-of-plane coordinates or displacements are about ±5 and ±25 μm, respectively, and the maximum errors in surface strain mapping are about 0.1% or less based on a series of evaluation tests on flat and curved sample surfaces over a physical field of view of 15.2 × 11.4 mm². As an application example, the shape and surface plastic strain distribution example, the shape and surface plastic strain distributions around a bent apex of a flat 2 mm thick automotive aluminum AA5182-O sheet, which underwent a 90° bend with three bend ratios of 2t, 1t, and 0.6t, are determined using the proposed technique.     

爆炸成型弹丸贯穿混凝土的实验研究

介绍几种聚能装药对混凝土层的破坏效果，并对聚能装药的结构设计与破坏效果的相互关系进行了分析与讨论。文中重点对截卵形药型罩、亚半球变壁厚药型罩、双功能药型罩的装药结构、破甲能力及目标结构特性进行了研究。     

Reliable solutions to the problem of periodic oscillations of an elastoplastic beam

We consider time-periodic oscillations of a beam with a spatially inhomogeneous Prandtl–Ishlinskii constitutive law describing the elastoplastic hysteresis. The data (mass density, Prandtl–Ishlinskii distribution, external load) are assumed to be uncertain. It is shown that a unique solution exists and is stable with respect to the data variation. Considering the total dissipated energy as a measure for the accumulated material fatigue, we identify and estimate from above the ‘worst scenario’ case, where the dissipation over one period is maximal within an admissible set of data obtained from inaccurate measurements.     

On the dynamic behaviour of a flexible beam carrying a moving mass

The behaviour of a system containing a mass traveling on a cantilever beam is considered. The mass is induced to move by an applied force as opposed to the case which has been considered in most literature where the position of the moving mass is assumed to be known and independent of the motion of the beam. Furthermore, the system to be discussed has the unique characteristic that the motions of the mass and the beam are coupled. The mathematical model of the system includes two coupled nonlinear integral/partial differential equations which are impossible to solve analytically and are difficult to solve numerically in their original form. As a remedy, the solution is discretized into space and time functions and the equations of motion are reduced to a set of ordinary differential equations. The shape function is chosen so that it satisfies the boundary conditions of the beam as well as the transient conditions imposed by the traveling mass. This choice of the shape function, which considers the mass-beam interaction, provides an improvement over the conventional method of using a simple cantilever beam mode shapes.The ordinary differential equations of motion using the improved shaped functions, are solved numerically to obtain the dynamic behaviour of the system. The results illustrate the validity of the model, and demonstrate the advantages of the improved model to the un-improved equations.     

A quasi-flow constitutive model with strain-rate dependence

In this paper, the proposed is a quasi-flow constitutive model with strain-rate sensitivity for elastic plastic large deformation. The model is based on the Quasi-flow Corner theory, and is suitable for the sheet metal forming process simulation with a variable punch machine velocity. Uniaxial tensile tests and deep-drawing tests of a circular blank with square punch are carried out and numerically simulated. The consistency between the experimental and the numerically simulated results shows the validity of the present new constitutive model. The project supported by the Scientific Foundation of National Outstanding Youth of China (10125208), the National Natural Science Foundation of China (19832020), and the National Education Committee of China     

Synthesis, spectroscopic characterization, DFT studies and biological assays of a novel gold(I) complex with 2-mercaptothiazoline

A new gold(I) complex with 2-mercaptothiazoline (MTZ) with the coordination formula [AuCN(C₃H₅NS₂)] was synthesized and characterized by chemical and spectroscopic measurements, DFT studies and biological assays. Infrared (IR) and ¹H, ¹³C and ¹⁵N nuclear magnetic resonance (NMR) spectroscopic measurements indicate coordination of the ligand to gold(I) through the nitrogen atom. Studies based on DFT confirmed nitrogen coordination to gold(I) as a minimum of the potential energy surface with calculations of the hessians showing no imaginary frequencies. Thermal decomposition starts at temperatures near 160 °C, leading to the formation of Au⁰ as the final residue at 1000 °C. The gold(I) complex with 2-mercaptothiazoline (Au-MTZ) is soluble in dimethyl sulfoxide (DMSO), and is insoluble in water, methanol, ethanol, acetonitrile and hexane. The antibacterial activities of the Au-MTZ complex were evaluated by an antibiogram assay using the disc diffusion method. The compound showed an effective antibacterial activity against Staphylococcus aureus (Gram-positive) and Escherichia coli and Pseudomonas aeruginosa (Gram-negative) bacterial cells. Biological analysis for evaluation of the cytotoxic effect of the Au-MTZ complex was performed using HeLa cells derived from human cervical adenocarcinoma. The complex presented a potent cytotoxic activity, inducing 85% of cell death at a concentration of 2.0 μmol L⁻¹.     

Experimental evaluation and constitutive modeling of non-proportional deformation for asymmetric steels

Recently non-proportional deformation has received increased attention from researchers working in the area of experimental and computational modeling of metal deformation. However, most of them are numerical in nature with limited experimental data available, making it further difficult to model non-proportional deformation. In the present work, two-stage uniaxial tests, along with uniaxial cyclic and biaxial tests for different stress ratios, have been performed to evaluate deformation behavior of ultra-low carbon high strength automotive steel. Behaviors like cross-effect and hardening stagnation, which are attributed to the evolution of complex dislocation structures, were observed in this steel. It was also noticed that this steel exhibits tension-compression asymmetry. As for constitutive modeling, a modified asymmetric yield function is proposed to be used with a combined isotropic-kinematic hardening model. Also methods to account for the hardening stagnation during reverse loading and the cross-effect during two-stage deformation are proposed. The resulting constitutive model showed reasonably good agreement with experimental results.