Effect of local anisotropy on fatigue crack initiation in a coarse grained nickel-base superalloy

In the present work, theoretical approaches, based on grain orientation dependent Young's modulus and Schmid factor are used to describe the influence of local grain orientation on crack initiation behaviour of the coarse grained nickel base superalloy Ren\'e80. Especially for strongly anisotropic crystal structures with large grain size, such as the investigated material, the local elastic properties must be taken into account for assessment of fatigue crack initiation. With an extension of Schmid's law, the resulting shear stress amplitude, which triggers local cyclic plastic deformation, can be calculated depending on local Young's modulus and Schmid factor. A Monte Carlo simulation with 100,000 samples shows how random grain orientation affects these parameters. Furthermore, the product of Young's modulus and Schmid factor (called $E\cdot m$) is used as a parameter to determine how grain orientation influences resulting shear stress amplitude for given total strain amplitude. In addition to the theoretical work using that approach, this model is also validated using isothermal LCF experiments by determining local grain orientation influence on the crack initiation site using SEM-EBSD analyses.Comment: 8 pages, 8 figure

A Probabilistic Model for LCF

Fatigue life of components or test specimens often exhibit a significant scatter. Furthermore, size effects have a non-negligible influence on fatigue life of parts with different geometries. We present a new probabilistic model for low-cycle fatigue (LCF) in the context of polycrystalline metal. The model takes size effects and inhomogeneous strain fields into account by means of the Poisson point process (PPP). This approach is based on the assumption of independently occurring LCF cracks and the Coffin-Manson-Basquin (CMB) equation. Within the probabilistic model, we give a new and more physical interpretation of the CMB parameters which are in the original approach no material parameters in a strict sense, as they depend on the specimen geometry. Calibration and validation of the proposed model is performed using results of strain controlled LCF tests of specimens with different surface areas. The test specimens are made of the nickel base superalloy RENE 80.Comment: 20 pages, 6 figure

Strain Analysis by a Total Generalized Variation Regularized Optical Flow Model

In this paper we deal with the important problem of estimating the local strain tensor from a sequence of micro-structural images realized during deformation tests of engineering materials. Since the strain tensor is defined via the Jacobian of the displacement field, we propose to compute the displacement field by a variational model which takes care of properties of the Jacobian of the displacement field. In particular we are interested in areas of high strain. The data term of our variational model relies on the brightness invariance property of the image sequence. As prior we choose the second order total generalized variation of the displacement field. This prior splits the Jacobian of the displacement field into a smooth and a non-smooth part. The latter reflects the material cracks. An additional constraint is incorporated to handle physical properties of the non-smooth part for tensile tests. We prove that the resulting convex model has a minimizer and show how a primal-dual method can be applied to find a minimizer. The corresponding algorithm has the advantage that the strain tensor is directly computed within the iteration process. Our algorithm is further equipped with a coarse-to-fine strategy to cope with larger displacements. Numerical examples with simulated and experimental data demonstrate the very good performance of our algorithm. In comparison to state-of-the-art engineering software for strain analysis our method can resolve local phenomena much better

A cost-sensitive learning algorithm for fuzzy rule-based classifiers

Designing classifiers may follow different goals. Which goal to prefer among others depends on the given cost situation and the class distribution. For example, a classifier designed for best accuracy in terms of misclassifica- tions may fail when the cost of misclassification of one class is much higher than that of the other. This paper presents a decision-theoretic extension to make fuzzy rule generation cost-sensitive. Furthermore, it will be shown how interpretability aspects and the costs of feature acquisition can be ac- counted for during classifier design. Natural language text is used to explain the generated fuzzy rules and their design proces

Mid-infrared characterization of thiophene-based thin polymer films

AbstractOptical properties of seven regioregular poly(3-alkylthiophene) with different alkyl side chain lengths which are poly(3-butylthiophene-2,5-diyl) (P3BT), poly(3-pentylthiophene-2,5-diyl) (P3PT), poly(3-hexylthiophene-2,5-diyl) (P3HT), poly(3-heptylthiophene-2,5-diyl) (P3hept), poly(3-octylthiophene-2,5-diyl) (P3OT), poly(3-decylthiophene-2,5-diyl) (P3DT), and poly(3-dodecylthiophene-2,5-diyl) (P3DDT) have been studied in the mid-infrared (IR) spectral region by means of Fourier Transformation Infrared (FTIR) spectroscopy and IR spectroscopic ellipsometry (IRSE). Absorbance spectra obtained in this fingerprint region are potential to characterize the structures formed by organic molecules in thin films due to molecular vibrations in detail. In consequence, the vibrational absorption bands of these seven samples demonstrated that P3PT, P3HT, and P3hept exhibited very similar band profiles, in contrast, the stretching vibration of thiophene rings (≈1465cm−1: CC) underwent a blue shift in P3BT, P3OT, P3DT and P3DDT. The highest value of the real part (ɛ1) of the complex dielectric constant was obtained from P3HT on both indium thin oxide (ITO) and silicon (Si) substrates whereas the imaginary part (ε2) was directly affected by increasing in the alkyl side chain lengths in a frequency range around 3000cm−1. The optical properties of P3PT in the mid-IR region developed an affinity with those of P3HT. Thus, P3PT is particularly a suitable polymer active material candidate for high-performance devices

Energy of sections of the Deligne–Hitchin twistor space

We study a natural functional on the space of holomorphic sections of the Deligne–Hitchin moduli space of a compact Riemann surface, generalizing the energy of equivariant harmonic maps corresponding to twistor lines. We show that the energy is the residue of the pull-back along the section of a natural meromorphic connection on the hyperholomorphic line bundle recently constructed by Hitchin. As a byproduct, we show the existence of a hyper-Kähler potentials for new components of real holomorphic sections of twistor spaces of hyper-Kähler manifolds with rotating S1-action. Additionally, we prove that for a certain class of real holomorphic sections of the Deligne–Hitchin moduli space, the energy functional is basically given by the Willmore energy of corresponding equivariant conformal map to the 3-sphere. As an application we use the functional to distinguish new components of real holomorphic sections of the Deligne–Hitchin moduli space from the space of twistor lines. © 2020, The Author(s)

Spreadsheet-Fehlermuster

In den Achtzigern begann eine weitgehende Verbreitung von Spreadsheets in der Industrie als Folge davon, das Spreadsheet-Software für den PC erschienen ist, mit der auch nicht-programmiererfahrene Endnutzer Spreadsheets erzeugen und bearbeiten konnten. Heutzutage sind sie in fast allen Unternehmen nicht mehr weg zu denken. Jedoch zeigen viele Studien, dass ein Großteil dieser Spreadsheets Fehler enthalten und dadurch jährlich hohe Schäden verursachen. Obwohl Prüfwerkzeuge für Spreadsheets existieren, sind sie auf Grund von entwurfstechnischen Einschränkung in der Industrie nur in geringem Maße einsetzbar. Deshalb wurde an der Universität Stuttgart in bisher je 2 abgeschlossenen Diplom- und Bachelorarbeiten das Spreadsheet Inspection Framework erstellt. Das Ziel des Spreadsheet Inspection Frameworks ist es durch statische und dynamische Prüfungen, die selber erstellt und konfiguriert werden können, auf Fehler im Spreadsheet aufmerksam zu machen. In dieser Arbeit wurden Fehlermuster entwickelt um die statischen Prüfungen des Spreadsheet Inspection Frameworks zu erweitern. Das Fehlermuster "Einer unter Anderen" erkennt Schemata und davon abweichende Zellen finden. "Separate Mehrfachreferenzierung in Formeln" deckt Fehler beim Erstellen von Funktionen auf. "Eingaben an nicht berücksichtigten Stellen" erkennt sowohl falsche als auch fehlende Referenzierungen. Zudem werden Werte erkannt, die in falsche Zellen gesetzt wurden. Das Fehlermuster "Referenzierung auf null-Werte" durchsucht das Spreadsheet nach Referenzierungen, die sich auf eine leere Zelle beziehen. Das "Wortdistanz" Muster sucht mit Hilfe des Levenshtein Algorithmus nach Tippfehlern.In the 1980s began a wide dissemination of spreadsheets in the industry as a result of the release of spreadsheet-software which allow end-users without programming experience to create and handle spreadsheets. It's inconceivable for most companies to work without spreadsheets. Many studies show that most of these spreadsheets contain errors and as a consequence there are high damages per year. Although there are tools for spreadsheets, they are rarely used in the industry because of conceptual restrictions. Because of that the Spreadsheet Inspection Framework was developed at the University Stuttgart as part of two finished diploma thesis and two finished bachelor thesis. The objective of the Spreadsheet Inspection Framework is it to red-flag errors with the help of static and dynamic tests, which can be developed and configurated on their one. In this Thesis smell patterns were developed to enhance the static inspections of the Spreadsheet Inspection Framework. The smell pattern "Einer unter Anderen" recognizes schemata and cells which goes against it. "Separate Mehrfachreferenzierung in Formeln" shows errors at the creating of formulas. "Eingaben an nicht berücksichtigten Stellen" recognizes false and missing references. Furthermore it perceives values which were set into a false cell. The smell pattern "Referenzierung auf null-Werte" searches for references that point to a null value. The "Wortdistanz" pattern searches on the basis of the Levenshtein algorithm for typing errors