Experimental evaluation of strains in the tension–compression using a new tool geometry, X-Die

Sheet-metal forming involves a complex distribution of strains throughout the part. The strains occur due to tension, compression and a mix of both. A geometry has been developed, the X-Die, in order to gain insight into the strain behavior of different materials. The X-Die enables strain paths far into the tension–compression region, thus creating the possibility to extend the experimental base both for definition and for further extrapolation of the forming limit curve (FLC) in the tension–compression region, as well as to evaluate FE-simulation results for the same region.

The experimental results show that the strain signature is impacted by material quality. In qualities such as extra high strength steel (EHSS) and aluminum the strains do not reach as far into the tension–compression region as the strains do in e.g. mild steel. This is due to failure in plane strain tension. Strain paths in materials such as mild steel and high strength steel (HSS) reach far into the tension–compression region before failure. Use of the X-Die provides possibilities to reach farther into the tension–compression region compared with traditional test methods for creating a forming limit diagram (FLD).

Use of the X-Die yields well-defined strain signatures. These clearly defined strain signatures are favorable for comparison with numerical simulations, especially for strain signatures in the tension–compression region.

Furthermore, the experiments using the X-Die indicate that a possible additional forming limit curve, which intersects the original forming limit curve (shear failure), exists so far into the tension–compression region that it is not applicable.

Even though the experiments indicate compression strains >100% (material DX56D), the experiments show potential for an experimentally determined extrapolation of the FLC up to 75% compression strain. The results of the experiments indicate that the X-Die geometry is suitable as a supplementary tool in identifying the strain behavior of different materials far into the tension–compression region and is also a good tool for verification of numerical results in the tension–compression region.     

Guest Editors' Introduction: Tablet PC Technology--The Next Generation

Early adopters in higher education have developed Tablet PC teaching platforms that incorporate active learning techniques and support in-class collaborations.     

On the physics of power,energy and economics of renewable electric energy sources – Part I

Environmental concerns have increasingly led to the installation of Renewable Energy Technologies (RETs) despite the fact that they are recognized as expensive. Innovative efforts within the area are beset with difficulties [1], and they are at risk of producing misdirected or insignificant improvements in terms of the cost effectiveness of total energy conversion systems. This paper investigates how RETs can be evaluated, in terms of economy and engineering solutions, by studying the fundamental physics of renewable energy sources and how it matches with the RETs. This match is described by the “Degree of Utilization”. The findings indicate that new innovations should focus on the possible number of full loading hours. RETs that are correctly matched to their energy source generate a higher amount of electric energy and have a higher potential of becoming more competitive. In cases where this aspect has been ignored, leading to relatively small degrees of utilization, it can be understood as an engineering mismatch between installed power, converted energy, and the fundamental physics of the renewable energy sources. Since there is a strong and possibly biased support for so-called mature RETs and already existing solutions, a clarification of how fundamental physical laws affect the cost of investments and payback of investments is needed. The present paper is part I out of II and it focuses on the difference between power and energy and the physics of different energy sources and their utilization.     

Wheat quality in organic and conventional farming: results of a 21 year field experiment

Consumers have become more aware of healthy and safe food produced with low environmental impact. Organic agriculture is of particular interest in this respect, as manifested by 5.768 million hectares managed pursuant to Council Regulation (EEC) 2092/91 in Europe. However, there can be a considerable risk that the avoidance of chemical inputs in organic farming will result in poor food quality. Here the results of a study on the quality of wheat (Triticum aestivum L.) grown in a 21 year agrosystem comparison between organic and conventional farming in central Europe are reported. Wheat was grown in a ley (grass/clover) rotation. The 71% lower addition of plant‐available nitrogen and the reduced input of other means of production to the organic field plots led to 14% lower wheat yields. However, nutritional value (protein content, amino acid composition and mineral and trace element contents) and baking quality were not affected by the farming systems. Despite exclusion of fungicides from the organic production systems, the quantities of mycotoxins detected in wheat grains were low in all systems and did not differ. In food preference tests, as an integrative method, rats significantly preferred organically over conventionally produced wheat. The findings indicate that high wheat quality in organic farming is achievable by lower inputs, thereby safeguarding natural resources. Copyright © 2007 Society of Chemical Industry     

LANDSAT test of diffuse reflectance models for aquatic suspended solids measurement

LANDSAT radiance data were used to test mathematical models relating diffuse reflectance to aquatic suspended solids concentration. Digital CCT data for LANDSAT passes over the Bay of Fundy, Nova Scotia were analyzed on a General Electric Co. Image 100 multispectral analysis system. Three data sets were studied separately and together in all combinations with and without solar angle correction. Statistical analysis and chromaticity analysis show that a nonlinear relationship between LANDSAT radiance and suspended solids concentration is better at curve-fitting than a linear relationship. In particular, the quasi-single-scattering diffuse reflectance model developed by Gordon and coworkers is corroborated. The Gordon model applied to 33 points of MSS 5 data combined from three dates produced r = 0.98.     

Determination of halogenated organic compounds and mutagenicity testing of spent bleach liquors.

The content of organohalogenated compounds in spent bleach liquor from different bleaching stages in a sulphate and a sulphite plant has been determined by a combination of glass capillary gas chromatography, gas-liquid chromatography/mass spectrometry and neutron activation analysis. Several compounds which have not been reported before have been identified including halogenated derivatives of dimethyl-propylnaphthalenes and alkylated catechols. The unconcentrated effluents, non-polar and total extracts were tested for mutagenic activity with Ames' Salmonella test. Spent bleach liquors from most bleaching stages as well as the total effluents contained mutagenic compounds. Addition of liver microsomes for metabolic activation reduced the mutagenic activity in all stages except for the first chlorination stage in the sulphate plant. Two isomers of chloro-, bromo-, and dichloro-p-cymene previously determined in effluents from bleaching plants were synthesized from the parent molecule. Both bromo- and dichloro-p-cymene exhibited weak mutagenic activity in the Salmonella test system. Liver microsomes reduced the effect slightly. The chlorinated cymenes were found to account for up to 18% of the total organically-bound chlorine in the non-polar extracts.     

In vitro evaluation of betamethasone-loaded nanoparticles

The aim of the present work was to investigate the preparation of nanoparticles as a potential drug carrier in the treatment of various inflammatory diseases. A nanoprecipitation method was used to entrap betamethasone in a poly[ε-caprolactone] matrix. Process parameters such as the initial drug load, the surfactants (polyvinyl alcohol, PVA; sodium cholate, SC), and their concentration in the aqueous phase were analyzed for their influences on particle properties. Particle size changed with increasing surfactant concentrations (PVA: 250 to 400 nm; sodium cholate: 330 to 150 nm) due to changes in interface stability and viscosity of the aqueous phase. The zeta potential was around neutrality with PVA and between - 28 and - 42 mV with SC. Betamethasone encapsulation rates of about 75% and 90% slightly increased with higher surfactant concentration. Drug release profiles exhibited an initial burst release with both surfactants, PVA (8-18%) or SC (25-35%) followed by a sustained release delivering 15% to 40% of the entrapped drug within 48 hours. The present nanoparticulate formulations exhibit promising properties of a colloidal drug carrier for betamethasone. Although SC seems to be advantageous due to its biocompatibility, in terms of sustained drug release pattern, the use of PVA is favorable.     

On application of differential geometry to computational mechanics

Developments in the fields of computational science—the finite element method—and mathematical foundations of continuum mechanics result in many new algorithms which give solutions to very complicated, complex, large scaled engineering problems. Recently, the differential geometry, a modern tool of mathematics, has been used more widely in the domain of the finite element method. Its advantage in defining geometry of elements [13–15] or modeling mechanical features of engineering problems under consideration [4–7] is its global character which includes also insight into a local behavior. This fact comes from the nature of a manifold and its bundle structure, which is the main element of the differential geometry.

Manifolds are generalized spaces, topological spaces. By attaching a fiber structure to each base point of a manifold, it locally resembles the usual real vector spaces; e.g. ³. The properties of a differential manifold M are independent of a chosen coordinate system. It is equivalent to say, that there exists smooth or C^r differentiable atlases which are compatible.

In this paper a short survey of applications of differential geometry to engineering problems in the domain of the finite element method is presented together with a few new ideas.

The properties of geodesic curves have been used by Yuan et al. [13–15], in defining distortion measures and inverse mappings for isoparametric quadrilateral hybrid stress four- and eight-node elements in ². The notion of plane or space curves is one of the elementary ones in the theory of differential geometry, because the concept of a manifold comes from the generalization of a curve or a surface in ³.

Further, the real global nature of differential geometry, has been used by Simo et al. [4,6,7]. A geometrically exact beam finite strain formulation is defined. The mechanical basis of such a nonlinear model can be found in the mathematical foundation of elasticity [18]. An abstract infinite dimensional manifold of mappings, a configuration space, is constructed which permits an exact linearization of algorithms, locally. A similar approach is used by Pacoste [5] for beam elements in instability problems.

Special attention is focused on quadrilateral hybrid stress membrane elements with curved boundaries which belong to a series of isoparametric elements developed by Yuan et al. [14]. The distortion measures are redefined for eight-node isoparametric elements in ² for which geodesic coordinates are used as local coordinates.     

Design of stop-band filter by use of curved pipe segments and shape optimization

It is often desirable to isolate some parts of a compound slender spatial structure from vibrations in connected substructures. An example of such a problem is found in domestic pipe systems where vibration from pumps and valves installed in an assembled pipe system should be suppressed before it reaches installations in dwellings. By use of Floquet theory and a shape optimization procedure a stop-band design is tuned into a specified frequency range. The structures with prescribed stop-band characteristics are composed of curved and straight pipe segments. For comparison vibro-acoustic energy transmission analysis is made on periodic piping systems where a finite series of the same substructures are implemented as a stop-band filter. The influence of production tolerances of such a stop-band filter is also assessed.