Mechanical and structural characterization of nonsintered and sintered steel wools by x-ray tomography: Description of t
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C. Barbier LAMCOS, INSA Lyon 18-20, rue des Sciences F69621 Villeurbanne Cédex, France
L. Salvo and Y. Bréchet SIMAP Institut National Polytechnique de Grenoble, 38402 Saint Martin d’Hères, France
O. Bouaziz ArcelorMittal Research, Voie Romaine, 57283 Maizières Les Metz, France; and Centre des Matériaux/Mines Paris, Paristech, CNRS-UMR7633, 91003, Evry cedex, France
D. Bouvard SIMAP Institut National Polytechnique de Grenoble, 38402 Saint Martin d’Hères, France (Received 23 May 2013; accepted 10 September 2013)
Properties of entangled materials, made of fibers, depend on the number and the nature of contacts between fibers and fibers orientation. Nonsintered and sintered steel wools have been characterized by x-ray tomography to extract structural information such as fibers orientation and number of contacts before and during compression. Image analysis techniques were developed on tomography images and validated on virtual materials, generated and deformed by numerical simulation based on molecular dynamic equations. The structural parameters measured during the structural characterization were finally used to link the structure of the studied material with the measured mechanical properties. To do this link, an analytical model usually used for this kind of material was modified to describe the evolution of mechanical properties in compression.
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.280
focused as a core material for sandwich structure.9–14 Indeed, they present an alternative to foams (metallic or polymeric). For certain metals (e.g., steel), foams are difficult to process because of high melting point, whereas the processing of fibers from the solid state is simpler. In the case of sandwich structure based on steel in automotive application for weldability issue, it is preferred to choose steel as the constitutive material of the core.15 From the previous reason, entangled materials made of steel fibers appear the best solution. In this context, increasing mechanical properties of entangled materials by the creation of permanent contacts between fibers is a possible solution. This can be done by several methods. In the literature, at least two means to create these contacts are studied: sintering, used for metallic fibers16–18 and spraying of epoxy glue, used for glass or carbon fibers.19 These studies show clearly the reinforcement in compression due to permanent contacts. In the case of nonpermanent contacts (nonbonded or sintered fibers), only densification is observed. When sufficient density of permanent contacts is created, behavior becomes similar to that of foams. Models developed on compression of entangled materials focused essentially on densification, such as the pioneered work of van Wyk20 and completed by Toll21 predicting a power law relationship between compression stress and relative density of materials. The
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Ó Materials Research Society 2013
I. INTRODUCTION
Entangled materials, made of fibers, find their major applications in t
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