Notch stress concepts for the fatigue assessment of welded joints - Background and applications

Among modern fatigue design concepts for welded structures, the linear-elastic notch stress concept gains increasing industrial acceptance. There are two variants of this concept, one for thick walled (t ? 5 mm) welded joints with the reference radius r_ref = 1.00 mm, which is already included in the fatigue design recommendations of the IIW and applied for the assessment of big welded structures, and one for thin walled (t < 5 mm) welded joints with the reference radius r_ref = 0.05 mm, which is more and more used in the automotive industry.The concept with r_ref = 1.00 mm is based on the micro-support theory of Neuber with the fictitious radius r_ref = 1.00 mm, derived by Radaj. The background of the concept with r_ref = 0.05 mm is the relationship between the stress-intensity factor and the notch stress according to Creager and Paris as well as Irvin’s theory of crack blunting. Besides these two theories, the definition of both of these radii has also an experimental background; they are observed in many welded joints.In the present paper, first the background and then different applications of both concept variants are described: the application of the reference radius of r_ref = 1.00 mm for MAG-welded offshore K-nodes (t = 30 mm) and sandwich panels for ship decks (t = 5 mm), and the application of r_ref = 0.05 mm for spot-welded automotive doors (t = 1 mm) and MAG-welded automotive trailing links (t = 3-4 mm). The sandwich panels were evaluated additionally with r_ref = 0.05 mm. Calculations and experimental results are compared and the reliability of the notch stress concept variants underlined. Additionally, recommendations for the slope of design lines distinguishing between thin and thick dimensions are given, i.e. k = 3.0 and 5.0 (normal stress, shear stress) for thick and stiff structures, k = 5.0 and 7.0 for thin and flexible structures.     

P3HT/PCBM Bulk Heterojunction Solar Cells: Impact of Blend Composition and 3D Morphology on Device Performance

The performance of polymer solar cells (PSC) strongly depends on the 3D morphological organization of the donor and acceptor compounds within the bulk heterojunction active layer. The technique of electron tomography is a powerful tool for studying 3D morphology of the layers composed of poly(3‐hexylthiophene) (P3HT) and a fullerene derivative ([6,6]‐phenyl‐C61‐butyric acid methyl ester; PCBM), especially to quantify the amount and distribution of fibrillar P3HT nanocrystals throughout the volume of the active layer. In this study, electron tomography is used to characterize P3HT/PCBM layers with different blend compositions, both before and after thermal annealing. The power conversion efficiency of the corresponding PSCs is strongly dependent on the overall crystallinity of P3HT and the way P3HT crystals are distributed throughout the thickness of the active layer.     

Efficient multispectral texture segmentation using multivariatestatistics

A complete, low computational cost method is presented for multispectral textured image segmentation. The procedure performs a tesselation of the image into non-overlapped rectangular regions and decides about the homogeneity of each region, using statistical hypothesis testing. Regions labelled as homogeneous are used to estimate the parameters that are necessary to classify the pixels of the heterogeneous regions. The proposed scheme can also be used to estimate the number of different textures in the image. This represents an efficient alternative to other computationally expensive methods, such as those that employ clustering techniques     

A variational treatment for the time dependent boltzmann equation as a basis for numerical solutions conserving neutrons

A maximum principle for the time-dependent first-order Boltzmann equation is established in two independent ways:- by a generalized least squares method and by a method based on the properties of an appropriate bi-linear form. The second derivation suggests a metric for a Hilbert space which provides a geometrical interpretation of the variational principle. This interpretation leads to a Petrov-Galerkin weighted residual method in contrast to the Galerkin method of Martin for time dependent transport.

The maximum principle is used to define a figure of merit for the global error of any numerical solution for time dependent transport. The principle is used also to demonstrate the neutron conservation property of optimized numerical solutions, and the convergence of finite element methods based on the variational principle.

A direct use of the maximum principle give a conservative three level scheme for transients in the angular flux. A less massive calculation for a conservative solution proceeds in two stages. The first stage obtains a preliminary solution based on a sequence of tailored steady state calculations for the even-parity angular flux. The relevant equations are derived by making residual terms vanish in the variational principle. They are equivalent to the finite element - finite difference equations used by de Oliveira and Wood for the analysis of oil-well logging by means of a neutron pulse. For the second stage the preliminary solution is weighted at each time step. The weights are determined by the maximum principle to yield a conservative solution which is continuous in time. The solution can be arranged to have also a continuous time derivative. Thus the maximum principle can be used both as a way of predicting and correcting solutions.     

Pseudo-cubic thin-plate-type spline method for analysing experimental data

This paper recalls the statistical origins of the minimum departure from nucleate boiling ratio (MDNBR) concept and Owen's coefficients, as used in CHF studies. The way in which they are currently used may be incorrect, and we shall present a new approach in which the lower tolerance interval limit depends on a number of parameters. The use of least-square regressions and smoothing splines is explained. We also include an example, based on a CHF EPRI test, from the Columbia University data bank.     

Fuzzy Online Auto-Tuning for an Industrial PID Controller

This paper presents a fuzzy tuning system for real-time industrial PID （proportional-integral-derivative） controllers. The algorithm set the proportional gain, integral time and derivative time of a classical PID structure according to the set point, error and error derivative of the process, respectively. The tuning of the PID controller is based on a fuzzy inference machine. The set of rules of the fuzzy inference machine was obtained by experts engineering. The system is tested in an austempering process but can be applied in any industrial plant. Besides, an analysis between the response of the process with a PID controller and the system of fuzzy auto-tuning for P1D proposed was made.