Compensating springback in the automotive practice\ud using MASHAL

New materials are used in the automotive industry to reduce weight and to improve crash performance. These\ud materials feature a higher ratio of yield stress to elastic modulus leading to increased springback after tool release. The resulting\ud shape deviations and their efficient reduction is of major interest for the automotive industry nowadays. The usual strategies for\ud springback reduction can diminish springback to a certain amount only. In order to reduce the remaining shape deviation a\ud mathematical compensation algorithm is presented. The objective is to obtain the tool geometry such that the part springs back\ud into the right shape after releasing the tools.\ud In practice the process of compensation involves different tasks beginning with CAD construction of the part, planning the\ud drawing method and tool construction, FE-simulation, deep drawing at try-out stage and measurement of the manufactured part.\ud Thus the compensation can not be treated as an isolated task but as a process with various restrictions and requirements of\ud today’s automotive practice. For this reason a software prototype for compensation methods MASHAL – meaning program to\ud maintain accuracy (MASsHALtigkeit) – was developed. The basic idea of compensation with MASHAL is the transfer and\ud application of shape deviations between two different geometries on a third one. The developed algorithm allows for an effective\ud processing of these data, an approximation of springback and shape deviations and for a smooth extrapolation onto the tool\ud geometry.\ud Following topics are addressed: positioning of parts, global compensation and restriction of compensation to local areas,\ud damping of the compensation function in the blank holder domain, simulation and validation of springback and compensation of\ud CAD-data. The complete compensation procedure is illustrated on an industrial part

Separation of bacterial spores from flowing water in macro-scale cavities by ultrasonic standing waves

The separation of micron-sized bacterial spores (Bacillus cereus) from a steady flow of water through the use of ultrasonic standing waves is demonstrated. An ultrasonic resonator with cross-section of 0.0254 m x 0.0254 m has been designed with a flow inlet and outlet for a water stream that ensures laminar flow conditions into and out of the resonator section of the flow tube. A 0.01905-m diameter PZT-4, nominal 2-MHz transducer is used to generate ultrasonic standing waves in the resonator. The acoustic resonator is 0.0356 m from transducer face to the opposite reflector wall with the acoustic field in a direction orthogonal to the water flow direction. At fixed frequency excitation, spores are concentrated at the stable locations of the acoustic radiation force and trapped in the resonator region. The effect of the transducer voltage and frequency on the efficiency of spore capture in the resonator has been investigated. Successful separation of B. cereus spores from water with typical volume flow rates of 40-250 ml/min has been achieved with 15% efficiency in a single pass at 40 ml/min.Comment: 11 pages, 6 figure

Ising Field Theory on a Pseudosphere

We show how the symmetries of the Ising field theory on a pseudosphere can be exploited to derive the form factors of the spin fields as well as the non-linear differential equations satisfied by the corresponding two-point correlation functions. The latter are studied in detail and, in particular, we present a solution to the so-called connection problem relating two of the singular points of the associated Painleve VI equation. A brief discussion of the thermodynamic properties is also presented.Comment: 39 pages, 6 eps figures, uses harvma

A mixed elastoplastic / rigid-plastic material model

A new integration algorithm is described for large strain plastic deformations. The algorithm degenerates to the Euler forward elastoplastic{plastic model for small strain increments and to the rigid{plastic model for large strain increments. The model benets from the advantages of both models: accuracy and fast convergence over a large range of strain increments

Design and characterization of dielectric filled TM110_{110} microwave cavities for ultrafast electron microscopy

Microwave cavities oscillating in the TM$_{110}$ mode can be used as dynamic electron-optical elements inside an electron microscope. By filling the cavity with a dielectric material it becomes more compact and power efficient, facilitating the implementation in an electron microscope. However, the incorporation of the dielectric material makes the manufacturing process more difficult. Presented here are the steps taken to characterize the dielectric material, and to reproducibly fabricate dielectric filled cavities. Also presented are two versions with improved capabilities. The first, called a dual-mode cavity, is designed to support two modes simultaneously. The second has been optimized for low power consumption. With this optimized cavity a magnetic field strength of 2.84 $\pm$ 0.07 mT was generated at an input power of 14.2 $\pm$ 0.2 W. Due to the low input powers and small dimensions, these dielectric cavities are ideal as electron-optical elements for electron microscopy setups