Andreas Rossoll

Nextel? 610 alumina fibre reinforced aluminium: Influence of matrix and process on flow stress

Abstract Continuous alumina fibre reinforced aluminium matrix composites are produced using two different liquid metal infiltration methods, namely direct squeeze casting and gas pressure infiltration. Net-shape fibre performs for longitudinal parallel tensile bars are prepared by winding the Nextel™ 610 alumina fibre (3M, St Paul, MN) into graphite moulds. High purity aluminium, two binary (Al–6% Zn and Al–1% Mg) and one ternary (Al–6% Zn–0.5% Mg) aluminium alloys are used as matrix materials. The composite is tested in uniaxial tension–compression, using unload–reload loops to monitor the evolution of Youngs modulus. A linear dependence between Youngs modulus and strain is observed; this is attributed, by deduction, to intrinsic elastic non-linearity of the alumina fibre. This conclusion is then used to compare on the basis of the in situ matrix flow curve the influence of matrix composition and infiltration process on the composite stress–strain behaviour.

Influence of heat treatment and particle shape on mechanical properties of infiltrated Al2O3 particle reinforced Al-2 wt-%Cu

Abstract Al-2 wt-%Cu composites were produced by gas pressure infiltration of powder beds with a high volume fraction (45 to 60 vol.-%) of angular or polygonal alumina particles. The tensile behaviour and fracture toughness of the composites were characterised in as cast, solutionised and peak aged (T6) conditions. It was shown that coarse intermetallics that are formed during solidification and located preferentially at the particle/matrix interface lead to lower toughness compared with the same composites in solutionised and T6 conditions. The particle nature and shape exert a strong influence on the properties of the composites: polygonal particles are intrinsically stronger than angular particles and yield stronger, tougher, and more ductile composites. Composite toughness variations are explained in terms of fracture micromechanisms.

Structural Metallic Materials by Infiltration

An overview is presented of current research at EPFL on structural metallic materials produced by infiltration processing. The paper comprises a brief introduction to the infiltration process, then presents results on particle reinforced metals and open-celled aluminium foams.

Transmitted light microscopy of a fibre reinforced metal

A method is presented for studying fibre damage in continuous fibre reinforced composites. It is based on contrasting the transmission of light through intact translucent fibres with the light through fractured or dead‐ended fibres. The method is applied in order to detect processing‐induced fibre fractures in aluminium reinforced with continuous alumina fibres.

The influence of non-linear elasticity on the determination of Weibull parameters using the fibre bundle tensile test

We address the influence of individual fibre stress‐ strain non-linearity on the extraction of Weibull-parameters from fibre bundle tensile tests. We extend the statistical theory of fibre bundle strength to include the non-linear elastic behaviour observed in many technically important fibres, e.g. glass-, carbon-, and alumina-fibres. It is shown that neglecting this non-linearity may lead to significant errors in determining the shape and scale parameters of the fibre fracture strength Weibull-distribution. A refinement of the existing extraction technique, accounting for this effect, is presented. The error resulting from neglecting the non-linear behaviour is assessed through a parametric study of the Weibull parameters for different levels of non-linearity. Explicit calculations are performed for two fibres of technical importance, namely Nextel 610e a-alumina fibre and a T300 carbon fibre. q 2003 Elsevier Ltd. All rights reserved.

Scaling of conductivity and Young’s modulus in replicated microcellular materials

Scaling exponents for the conductivity and stiffness of replicated microcellular materials exceed commonly predicted values of 1 and 2. We show here that this is caused by the fact that, in replicated microcellular materials, the solid architecture varies with the relative density: a simple derivation based on the physics of powder consolidation returns and explains the observed scaling behaviour. The same derivation also gives an explanation for Archie’s law, known to describe the conductivity of wet soils.

Fracture strength of alumina fiber reinforced aluminum wire with and without a torsional pre-strain

Abstract The influence of torsion applied prior to tensile testing on the fracture strength of Nextel™ 610 alumina continuous-fiber reinforced aluminum matrix composite wire is investigated. It is shown that internal stresses that develop in the composite upon twisting exert a dominant influence on the derived failure criteria, which exceeds that of fiber misalignment resulting from the gradual inclination during twisting of the fibers with respect to the wire axis. At low and intermediate levels of twisting up to a surface shear strain of 10%, fracture occurs when the sum of externally applied and internal stresses reaches locally the fracture stress of the untwisted material. For higher surface shear deformations, two possible fracture-stress vs surface shear strain dependencies are predicted, depending on the general fracture behavior of the composite qualified in terms of damage tolerance. Experiment shows that the fracture strength of the reinforced wire used in this study follows the behavior ascribed to a nondamage-sensitive material.

Erratum: Influence of heat treatment and particle shape on mechanical properties of infiltrated Al2O3 particle reinforced Al-2 wt-% Cu (Materials Science and Technology, (December 2002) 18 (1461-1470))

Keywords: error Note: 02670836 (ISSN) Reference LMM-ARTICLE-2003-005doi:10.1179/026708303225002956View record in Scopus Record created on 2006-10-09, modified on 2016-08-08