IWT - Foundation Institute of Materials Engineering

Bremen, Germany

IWT - Foundation Institute of Materials Engineering

Bremen, Germany
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Doicu A.,German Aerospace Center | Wriedt T.,IWT - Foundation Institute of Materials Engineering
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2010

In this paper we analyze three methods for computing the total field in the near-zone region. These methods use the expansion of the scattered field outside the minimum circumscribing sphere, an integral representation of the scattered field and a vector spherical wave expansion of the near-zone field. Calculations of the total field within the circumscribing sphere are presented for dielectric prolate spheroids to compare the different methods. © 2009 Elsevier Ltd. All rights reserved.


Caggiano A.,University of Buenos Aires | Said Schicchi D.,IWT - Foundation Institute of Materials Engineering
Engineering Structures | Year: 2015

This paper proposes a model aimed at simulating the bond behaviour of Fiber Reinforced Polymer (FRP) laminates glued to concrete substrates and exposed to high temperature. Based on a previous model already formulated by one of the authors and available in the scientific literature, the present paper proposes a theoretical model formulated within the general framework of Fracture Mechanics and Plasticity-based concepts. Particularly, the aforementioned model is extended herein to consider the thermal effects, through a temperature-based scaling function affecting the strength parameters and softening rules which define the failure surface and the post-cracking response of FRP-concrete joints. The mechanical soundness of the proposed model is demonstrated by the very good agreement between some experimental results taken from the scientific literature on FRP-to-concrete systems tested in pull-out loading at normal and elevated temperature and the corresponding theoretical simulations. © 2014 Elsevier Ltd.


Meyer D.,IWT - Foundation Institute of Materials Engineering
CIRP Annals - Manufacturing Technology | Year: 2012

In an advanced production line including cold surface hardening, martensitic transformation in metastable austenites as workpiece material was achieved by deep rolling. The deep rolling process replaces energy- and cost-intensive heat treatments. Cryogenic deep rolling is a novel approach to combine two different sources of energy (thermal and mechanical effects) and thereby allows for application of more stable microstructures. This comes along with advantages regarding soft machining and the stability of the core material during a component's functional loading. This paper presents the theoretical background, suitable parameters, and the resulting surface integrity of cryogenic deep rolled components and gives clear recommendations for industrial application. © 2012 CIRP.


Solter J.,IWT - Foundation Institute of Materials Engineering | Gulpak M.,IWT - Foundation Institute of Materials Engineering
CIRP Annals - Manufacturing Technology | Year: 2012

A predictive model for heat induced shape deviations would facilitate the optimization of dry milling strategies. Results from milling experiments aiming at a physically based regression model for the heat flux distribution along the contact arc are presented. The contact arc was discretised by varying the width of cut on four levels for each combination of cutting speed, feed speed, and depth of cut. Heat fluxes to the workpiece were iteratively determined in an inverse procedure. Heat partitioning not only depends on the thermal number as in orthogonal cutting but also on the feed speed and the depth of cut. © 2012 CIRP.


Grant
Agency: European Commission | Branch: FP7 | Program: ERC-AG | Phase: ERC-AG-PE8 | Award Amount: 2.27M | Year: 2011

The overall goal of the project is to elaborate the scientific foundations for possible future innovations in the application of metalworking fluids (MWFs). For most mechanical machining processes such as turning, milling, drilling, and grinding the use of MWFs is indispensable as they perform several essential functions in material removal processes, such as cooling of workpiece and tool, reduction of heat generation by lubrication, removal of chips and promotion of chemical reactions with the surface. In the past decades the scientific understanding of MWF effectiveness could not keep up with the rapid developments in the industrial application of MWFs. As a consequence of this lack of knowledge, todays MWFs consist of up to 60 chemical components with partly harmful properties and thus hazardous potential for the operator and the environment. Hence, this project will aim towards scientific based innovations and suggests a four-mission approach for stimulating a paradigm shift in MWF features and application. Research will include: a) fundamental research on physical, chemical, and microbial working mechanisms, which allows MWF components e.g., with controlled chemical activity, b) new MWF design e.g., the development of MWFs which consist of lubricating bacteria replacing todays paradigms such as the usage of additives and oil in water emulsions, c) simplified MWF maintenance and supply by e.g., in-process self-controlled chemical MWF composition and adaptation of the MWF supply system for temperature and force reduction, and d) verification and transfer of the innovative, alternative systems e.g., on a test bench in a realistic environment being part of a demonstration center. The distinguishing feature of the approach will be its cross-disciplinary and comprehensive nature.


Wriedt T.,IWT - Foundation Institute of Materials Engineering
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2012

Over the last decade many theories and computational tools have been developed to compute light scattering by particles, particles on plane surfaces and systems of particles. In this short discussion we look at the driving forces for the recent developments and at new concepts to determine if there are still open questions in the field of light scattering simulation. © 2012 Elsevier Ltd.


Rentsch H.,IWT - Foundation Institute of Materials Engineering
Materialwissenschaft und Werkstofftechnik | Year: 2012

The gear wheel manufacture is one of the key technologies for power train systems and in automotive industry. These complex high performance parts require stable processes and narrow tolerances in order to control the manufacturing costs. Experimental analyses show that the material flow in disk-like gear wheel blanks made of 20MnCr5 can vary significantly. This is of significance as a correlation between the dishing after case-hardening of the gear wheel blanks and the material flow was found. Besides experimental findings, finite element (FE) analyses of the influence of process parameters and perturbations on the distortion of forged gear wheel blanks have been carried out. A temperature gradient over the height of the workpiece is assumed to be largely responsible for the observed material flow variations and the related dishing of the forged gear wheel blanks. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Hunkel M.,IWT - Foundation Institute of Materials Engineering
Materialwissenschaft und Werkstofftechnik | Year: 2012

In general, material data for heat treatment simulations are assumed to be isotropic and homogeneous (except the carbon dependency for case hardening simulations). But it was found for the conventional continuous casted case hardening steel 20MnCr5 (SAE 5120) that segregations lead to anisotropic and inhomogeneous properties especially during phase transformations. This paper reviews the work within the Collaborative Research Centre SFB 570 "Distortion Engineering" on determination of segregations and its influence on phase transformations and plasticity as well as the subsequent modelling and simulation. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Zoch H.-W.,IWT - Foundation Institute of Materials Engineering
Materialwissenschaft und Werkstofftechnik | Year: 2012

The result of distortion during manufacturing and its removal or correction totally amounts to similar economical losses in industry as known by wear or corrosion phenomena. Therefore over a long time high efforts have been taken to avoid or minimize distortion, starting with basic investigations at the beginning of the last century. The increasing importance led to intensified research, culminating in the late 90's with several investigations on steel grades and productions routes and their impact on dimensional changes. Focussing on separated aspects and influencing parameters before, the establishment of the Collaborative Research Center "Distortion Engineering" at Bremen University, funded by the Deutsche Forschungsgemeinschaft (DFG), first time treated distortion as a system attribute and result of the entire process chain. After 11 years of project work in the CRC, which ends in 2011, a summary of achievements and outlook on further investigations is given. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Wriedt T.,IWT - Foundation Institute of Materials Engineering
Springer Series in Optical Sciences | Year: 2012

In optical particle characterisation and aerosol science today light scattering simulations are regarded as an indispensable tool to develop new particle characterisation techniques or in solving inverse light scattering problems. Mie scattering and related computational methods have evolved rapidly during the past decade such that scattering computations for spherical scatterers a few order of magnitudes larger, than the incident wavelength can be easily performed. This significant progress has resulted from rapid advances in computational algorithms developed in this field and from improved computer hardware. In this chapter the history and a review of the recent progress of Mie scattering and Mie-related light scattering theories and available computational programs is presented. We will focus on Mie scattering theories but as there is much overlap to related scattering theories they will also be mentioned where appropriate. Short outlines of the various methods are given. This review is of course biased by my interest in optical particle characterisation and my daily reading. © 2012 Springer-Verlag Berlin Heidelberg.

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