Evaluation of stresses in a combined plane strain-simple shear test

A biaxial testing device for sheet metal has been developed that can impose a combination of\ud plane strain and simple shear deformation. The specimen has a large width to height ratio and a small height\ud to thickness ratio. The forces in tensile and shear direction are easily measured and the tensile stress and shear\ud stress can easily be derived. For a full description of stresses, however, the stress in lateral direction should also\ud be known. This stress is a result of the constraint, imposed by the large width to height ratio and cannot be\ud measured directly. The strain in the specimen is measured on the surface. By imposing the Drucker normality\ud principle, the direction of the tangent to the yield surface is known and the unknown stress increment in lateral\ud direction can be obtained. Computer simulations are performed to test whether the intended approach can\ud recalculate all stress components from measurement of 3 in-plane strains and just 2 stresses. Without hardening,\ud good results are obtained for a complete interval between the pure shear point up to a point between uniaxial\ud stress and the plane strain point on the yield locus. With hardening, the algorithm requires a lot of data points\ud to avoid drifting from the exact solution. It is noted that, although the normality rule is used, it is not necessary\ud to have an a-priori knowledge of the yield functio

Improvements in FE-analysis of real-life sheet metal forming

An overview will be presented of recent developments concerning the application\ud and development of computer codes for numerical simulation of sheet metal forming\ud processes. In this paper attention is paid to some strategies which are followed to improve the\ud accuracy and to reduce the computation time of a finite element simulation. Special attention\ud will be paid to the mathematical modeling of the material deformation and friction, and the\ud effect of these models on the results of simulations. An equivalent drawbead model is\ud developed which avoids a drastic increase of computation time without significant loss of\ud accuracy. The real geometry of the drawbead is replaced by a line on the tool surface. When\ud an element of the sheet metal passes this drawbead line an additional drawbead restraining\ud force, lift force and a plastic strain are added to that element. A commonly used yield\ud criterion for anisotropic plastic deformation is the Hill yield criterion. This description is not\ud always sufficient to accurately describe the material behavior. This is due to the\ud determination of material parameters by uni-axial tests only. A new yield criterion is\ud proposed, which directly uses the experimental results at multi-axial stress states. The yield\ud criterion is based on the pure shear point, the uni-axial point, the plane strain point and the\ud equi-biaxial point

Inhomogeneous superconductivity induced in a weak ferromagnet

Under certain conditions, the order parameter induced by a superconductor (S) in a ferromagnet (F) can be inhomogeneous and oscillating, which results e.g. in the so-called pi-coupling in S/F/S junctions. In principle, the inhomogeneous state can be induced at T_c as function of the F-layer thickness d_F in S/F bilayers and multilayers, which should result in a dip-like characteristic of T_c(d_F). We show the results of measurements on the S/F system Nb/Cu_{1-x}Ni_x, for Ni-concentrations in the range x = 0.5-0.7, where such effects might be expected. We find that the critical thickness for the occurrence of superconductivity is still relatively high, even for these weak ferromagnets. The resulting dip then is intrinsically shallow and difficult to observe, which explains the lack of a clear signature in the T_c(d_F) data.Comment: 4 pages, 4 figures. To be publishedin Physica C (proceedings of the Second Euroconference on Vortex Matter in Superconductors, Crete, 2001

The construction of confidence intervals for frequency analysis using resampling techniques: a supplementary note

International audienceIn a recent contribution, Hall et al. (2004) examined the use of the Bootstrap resampling technique as a means of constructing confidence limits for the quantiles of the (two-parameter) Gumbel and the (three-parameter) Weibull distributions. Particular emphasis was placed on the behaviour of sample sizes of the order of 30, which are typical of those encountered in hydrological frequency analysis. The resampled confidence limits obtained for the Gumbel distribution were found to be comparable with those based upon a well-known theoretical approximation. However, those for samples of size 30 from the Weibull distribution were shown to be more problematical, with the results dependent upon the skewnesses of the resampled distributional parameters. For a further and more quantitative assessment of the suitability of Bootstrap resampling for constructing confidence intervals, so-called coverage rates were evaluated for the Weibull distribution in a supplementary study. The results show a satisfactory performance when using the percentile method but do not really mitigate the conclusion of the original study that resampled confidence limits should be employed with caution when sample sizes are of the order of 30. Keywords: Bootstrap, Jack-knife, frequency analysis, maximum likelihood method, maximum product of spacings method, confidence intervals, coverage rate

ON THE EXPRESSIVE POWER OF THE RELATIONAL MODEL: A DATABASE DESIGNER\u27S POINT OF VIEW

The purpose of this paper is to introduce a framework for assessing the expressive power of data models and to apply this framework to the relational model of data. From a designer\u27s point of view, a data model such as the relational model should not only be formally defined and easy to understand, but should also provide a powerful set of constructs to model real-world phenomena. The expressive power of a data model, defined as the degree to which its constructs match with constructs encountered in reality, can be judged by two complementary principles: the interpretation principle and the representation principle. It is asserted that database designers attempt to minimize the number of ad hoc database constraints, and that a data model faithful to the two principles supports this design strategy. Subsequently, this constraint minimization strategy is used to assess the expressive power of a particular data model, i.e., the relational data model. The authors take the position that the expressive power of the relational model is not optimal, due to a lack of adherence to both the interpretation principle and the representation principle. The paper amplifies this position by means of a number of examples, all based on publications by Codd and Date

The MUSE-Wide Survey: Survey Description and First Data Release

We present the MUSE-Wide survey, a blind, 3D spectroscopic survey in the CANDELS/GOODS-S and CANDELS/COSMOS regions. Each MUSE-Wide pointing has a depth of 1 hour and hence targets more extreme and more luminous objects over 10 times the area of the MUSE-Deep fields (Bacon et al. 2017). The legacy value of MUSE-Wide lies in providing "spectroscopy of everything" without photometric pre-selection. We describe the data reduction, post-processing and PSF characterization of the first 44 CANDELS/GOODS-S MUSE-Wide pointings released with this publication. Using a 3D matched filtering approach we detected 1,602 emission line sources, including 479 Lyman-$\alpha$ (Lya) emitting galaxies with redshifts $2.9 \lesssim z \lesssim 6.3$. We cross-match the emission line sources to existing photometric catalogs, finding almost complete agreement in redshifts and stellar masses for our low redshift (z < 1.5) emitters. At high redshift, we only find ~55% matches to photometric catalogs. We encounter a higher outlier rate and a systematic offset of $\Delta$z$\simeq$0.2 when comparing our MUSE redshifts with photometric redshifts. Cross-matching the emission line sources with X-ray catalogs from the Chandra Deep Field South, we find 127 matches, including 10 objects with no prior spectroscopic identification. Stacking X-ray images centered on our Lya emitters yielded no signal; the Lya population is not dominated by even low luminosity AGN. A total of 9,205 photometrically selected objects from the CANDELS survey lie in the MUSE-Wide footprint, which we provide optimally extracted 1D spectra of. We are able to determine the spectroscopic redshift of 98% of 772 photometrically selected galaxies brighter than 24th F775W magnitude. All the data in the first data release - datacubes, catalogs, extracted spectra, maps - are available on the website https://musewide.aip.de. [abridged]Comment: 25 pages 15+1 figures. Accepted, A&A. Comments welcom