Towards the Contact and Impact Modeling in Finite Element Simulations of High Speed Forming

In finite element simulations of high speed sheet metal forming processes the contact between workpiece and forming tools has to be modeled very carefully. Several important aspects have to be taken into account. Robust and locking-free finite element formulations are required to model the sheet forming process, the die has to be considered as a deformable component, and the description of the contact constraints between workpiece and forming tools is a significant source of shortcomings in modeling. The contact and impact simulation makes high demands on the robustness of finite element formulations. For this reason finite elements with low order ansatz functions are preferred. Furthermore, they prove to be advantageous when automatic meshing tools are applied. To overcome the undesired effects of locking we work with an improved version of the innovative solid-shell concept proposed by [11]. It is based on the concept of reduced integration with hourglass stabilization. The use of this solid-shell finite element allows us to test the influence of the modeling of the die and the contact constraints in a very efficient way. An overview of so-called macro and micro deformations of forming tools in sheet metal forming simulations can be found in [8]. We show that the deformation of the die has a noticeable influence in electromagnetic sheet metal forming. However, in most commercial finite element codes taking into account elastically deformable forming tools requires a full finite element discretization of the die which leads to very high computational effort. Therefore users often assume the tools as being rigid and apply node-based spring-dashpot systems to improve the modeling of the interaction between sheet metal and die. But also in this case local interactions cannot be taken into account realistically. As a possible remedy we investigate a fully elastic description of the forming tools in combination with model reduction techniques. These significantly reduce the number of degrees-of-freedom in the finite element simulation. For this reason we present different alternatives of this technique

Automated image processing for quantification of blue-stain discolouration of Norway spruce wood

Bioincising is a promising method for enhancing liquid uptake (e.g. preservatives or wood-modification agents) in refractory wood. Incubation with the white-rot fungus, Physisporinus vitreus, which selectively degrades pit membranes, results in deeper and more homogeneous penetration of liquids. Conventional methods of assessing the degree of fungal discolouration of wood after treatment with preservatives (e.g. European standard EN 152) are partly based on a subjective rating scale, which gives a rough value of the surface colonisation by blue-stain fungi. Hence, an automated image processing (AIP) procedure was developed for standardised quantification of the segmentation thresholds of discolouration and tested against manual segmentation analysis. Using the red filter in the AIP method revealed high correlation (R 2 0.95) and allowed for more user friendly and objective determination of blue staining of woo

Efficient Finite Element and Contact Procedures for the Simulation of High Speed Sheet Metal Forming Processes

A large variety of forming processes is used in industrial manufacturing processes. The numerical simulation of such processes puts high demands on the finite element technology. Usually first order isoparametric elements are preferred because of their robustness and numerical efficiency. Unfortunately, these elements tend to undesired numerical effects like "locking", predominant in situations characterized by plastic incompressibility or pure bending. To overcome this problem, several authors [1, 2, 4] propose finite element formulations based on the concept of reduced integration with hourglass stabilization by applying the "enhanced strain method". The main advantage of the proposed new isoparametric solid-shell formulation with linear ansatz functions is the fact that the undesirable effects of locking are eliminated. The previously described element technique can be applied to analyze specific problems of high speed forming into a cavity: Working with contact surfaces discretized by first order finite elements leads to discontinuities of the normal patch vector and, subsequently, to non-smooth sliding [5]. In quasi-static forming processes these discontinuities will not influence the contact forces noticeably. However, in dynamic investigations the sudden change of contact forces due to the rough surface description leads to a very high acceleration of the contact nodes. To avoid this effect, a smoothing algorithm will be described

Supporting Counselors-in-Training: A Toolbox for Doctoral Student Supervisors

Counselor education doctoral students are often required to supervise master-level counselors-in-training as part of their supervision internship. While practical, this arrangement places doctoral students and their supervisees in potentially compromised situations, given their lack of experience in these respective roles. This article offers a toolbox of strategies doctoral student supervisors can use to facilitate their work with counselors-in-training. These strategies address focus areas identified through prior research. Doctoral student supervisors are encouraged to use this toolbox in conjunction with the support and guidance of their faculty supervisor as they navigate clinical supervision

Interferometry and higher-dimensional phase measurements using directionally unbiased linear optics

Grover multiports are higher-dimensional generalizations of beam splitters, in which input to any one of the four ports has equal probability of exiting at any of the same four ports, including the input port. In this paper, we demonstrate that interferometers built from such multiports have novel features. For example, when combined with two-photon input and coincidence measurements, it is shown that such interferometers have capabilities beyond those of standard beam-splitter-based interferometers, such as easily controlled interpolation between Hong-Ou-Mandel (HOM) and anti-HOM behavior. Further, it is shown that the Grover-based analog of the Mach-Zehnder interferometer can make three separate phase measurements simultaneously. By arranging the transmission lines between the two multiports to lie in different planes, the same interferometer acts as a higher-dimensional Sagnac interferometer, allowing rotation rates about three different axes to be measured with a single device

Enhanced-sensitivity interferometry with phase-sensitive unbiased multiports

Here we introduce interferometric devices by combining optical feedback (cavities) with unbiased multiports, which unlike traditional beam dividers, allow light to reflect back out of the port from which it originated. By replacing the traditional, directionally-biased beam-splitter in a Michelson interferometer with an unbiased multiport, the functional dependence of the scattering amplitudes changes. As a result, the derivative of transmittance with respect to an external phase perturbation can be made substantially large. This significantly enhances the resolution of phase measurement, and allows the phase response curves to be altered in real time by tuning an externally-controllable phase shift

One-particle inclusive CP asymmetries

One-particle inclusive CP asymmetries in the decays of the type B -> D(*) X are considered in the framework of a QCD based method to calculate the rates for one-particle inclusive decays.Comment: Latex, 13 pages, 6 figures (eps). Analytical and numerical results unchanged, extended discussion of model assumptions and systematic uncertainties. Version to be published in Phys. Rev. D 62, 0960xx. Additional transparencies are available via the WWW at http://www-ttp.physik.uni-karlsruhe.de/Slides

Learning from Minimum Entropy Queries in a Large Committee Machine

In supervised learning, the redundancy contained in random examples can be avoided by learning from queries. Using statistical mechanics, we study learning from minimum entropy queries in a large tree-committee machine. The generalization error decreases exponentially with the number of training examples, providing a significant improvement over the algebraic decay for random examples. The connection between entropy and generalization error in multi-layer networks is discussed, and a computationally cheap algorithm for constructing queries is suggested and analysed.Comment: 4 pages, REVTeX, multicol, epsf, two postscript figures. To appear in Physical Review E (Rapid Communications