C. San Marchi

Deformation of open-cell aluminum foam

The mechanical properties of high-purity aluminum foams produced by replication from salt precursors are measured in compression. These foams have homogeneous open-porosity, cell sizes equivalent to the particle size of the precursor salt (∼500 μm in this case) and relative densities near 25%. Deformation is uniform and strain hardening similar to the bulk material is observed without a plateau stress. A simple analytical model based on beam theory is employed to describe the flow stress and the change in stiffness of the foams as a consequence of compression. This model leads to a modified scaling law for the flow stress of metallic foams.

Influence of damage on the tensile behaviour of pure aluminium reinforced with ?40 vol. pct alumina particles

particle beds with high purityAl (99.99%). These materials feature 40–60 vol. pct reinforcement homogeneously distributed in a pore-freematrix. Their tensile behaviour is studied as a function of reinforcement size and shape. Internal damage, inthe form of particle fracture and matrix voiding, occurs from the onset of plastic straining. Its evolution withstrain is monitored through changes in (i) stiffness and (ii) peak stress after incremental plastic straining andannealing. The influence of damage on the flow curves of the composites can be accounted for using basicpostulates of continuum damage mechanics. Failure strains vary between 2 and 4%, and are a function ofthe rate of damage accumulation. An expression is derived to predict elongation to failure of damagingmaterials that fail by tensile instability, which gives good agreement with the experimental observations. 2001 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc.Keywords: Composites; Dislocations; Aluminium; Stress–strain relationship measurements; Damage1. INTRODUCTION

Alumina-aluminum interpenetrating-phase composites with three-dimensional periodic architecture

Robotic deposition was used to create an alumina structure with three-dimensional periodicity and submillimeter feature size. Liquid metal infiltration of this structure resulted in an Al2O3–Al interpenetrating-phase composite exhibiting low thermal expansion and high compressive strength. � 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Quantification of microdamage phenomena during tensile straining of high volume fraction particle reinforced aluminium

Particle reinforced composites are produced by infiltrating ceramic particle beds with 99.99% Al. Resulting materials feature a relatively high volume fraction (40-55 vol. pet) of homogeneously distributed reinforcement. The evolution of damage during tensile straining of these composites is monitored using two indirect methods; namely by tracking changes in density and in Youngs modulus. Identification and quantification of the active damage mechanisms is conducted on polished sections of failed tensile specimens: particle fracture and void formation in the matrix are the predominant damage micromechanisms in these materials. The damage parameter derived from the change in density at a given strain is found to be one to two orders of magnitude smaller than the parameter based on changes in Youngs modulus. A simple micromechanical analysis inspired by the observed damage micromechanisms is used to correlate the two indirect measurements of damage. The predictions of this analysis are in good agreement with experiment

Thermal expansion responses of pressure infiltrated SiC/Al metal-matrix composites

Aluminium-matrix composites containing thermally oxidized and unoxidized SiC particles featuring four average particle diameters ranging from 3 to 40 μm were produced by vacuum assisted high pressure infiltration. Their thermal expansion coefficient (CTE) was measured between 25 and 500°C. Oxidation of the SiC particles in air produces the formation at their surface of silicon oxide in quantities sufficient to bond the particles together, and confer strength to preforms. After infiltration with pure aluminium, the composites produced showed no sign of significant interfacial reaction. The CTE of the composite reinforced with unoxidized SiC particles featured an abrupt upward deviation upon heat-up near 200°C, and a second abrupt decrease near 400°C. The first transition is attributed to an inversion of stress across particle contact points. When composites are produced with oxidized SiC particles, these two transitions were removed, their CTE varying smoothly and gradually from the lower elastic bound to the upper elastic bound as temperature increases. With both composite types, the CTE decreased as the average particle size decreased. This work illustrates the benefits of three-dimensional reinforcement continuity for the production of low-CTE metal matrix composites, and shows a simple method for producing such composites.

Quasistatic and dynamic compression of aluminum-oxide particle reinforced pure aluminum

Keywords: Damage ; High strain rate ; Mechanical properties ; Particle-reinforced aluminum composites ; Plastic ; Cavitation ; Infiltration ; Metallic matrix composites ; Sensitivity analysis ; Strain rate ; Stresses ; Gas-pressure infiltration ; Alumina ; aluminum ; aluminum oxide ; damage ; mechanical property ; particle reinforced material ; strain ; damage Note: Laboratory for Mechanical Metallurgy, EPFL, Lausanne CH-1015, Switzerland Inner Mongolia Inst. of Metal Res., P.O. Box 4, Baotou, Inner-Mongolia 014034, China Department of Materials Science/Eng., Northwestern University, 2225 N. Campus Dr., Evanston, IL 60208-3018, United States09215093 (ISSN)DOI: 10.1016/S0921-5093(02)00035-7 Reference LMM-ARTICLE-2002-002doi:10.1016/S0921-5093(02)00035-7View record in Web of ScienceView record in Scopus Record created on 2006-10-09, modified on 2017-05-10

On the use of considere's criterion in tensile testing of materials which accumulate internal damage

Keywords: Aluminum ; Deformation ; Density (specific gravity) ; Mechanical properties ; Numerical methods ; Strain ; Stresses ; Tensile properties ; Tensile testing ; Particle reinforced aluminum composites ; Stress strain relationship measurement theory ; Stress strain tensile curve ; Tensile deformation ; Metallic matrix composites Note: Laboratory for Mechanical Metallurgy, Swiss Inst. Technol. Lausanne, C., Lausanne, Switzerland13596462 (ISSN)CODEN: SCMAF; DOI: 10.1016/S1359-6462(99)00159-1 Reference LMM-ARTICLE-1999-001doi:10.1016/S1359-6462(99)00159-1View record in Web of ScienceView record in Scopus Record created on 2006-10-09, modified on 2016-08-08

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.

Corrigendum to: on the tensile behaviour of infiltrated alumina particle reinforced aluminium composites

Abstract The purpose of this note is to correct two errors, which were present in the manuscripts of two articles published by ourselves in Acta Materialia and are not printer’s errors.

Melt infiltration processing of foams using glass-forming alloys

Processing of foams from bulk metallic glass (BMG) alloys, using melt infiltration techniques, is reported for the first time. Foaming methods based on infiltration of two types of pattern materials are described: investment of a continuous refractory yielding very low relative density structures (5% dense relative to the BMG), and investment of a discontinuous refractory pellet bed yielding higher relative density (50-60% dense relative to the BMG). Both methods are capable of producing foam structures; however high surface area and diminished thermal conductivity, especially in lower density structures, make vitrification of the alloy difficult.