Notch (In)Sensitivity of Aluminum Matrix Syntactic Foams.

Attila Szlancsik,Dóra Károly,Bálint Katona,Imre Orbulov

doi:10.3390/ma12040574

Abstract

Aluminum alloy (Al99.5 or AlSi12)-based metal matrix syntactic foams (MMSFs) were produced by pressure infiltration with ~65 vol % Globocer filler (33 wt % Al2O3, 48 wt % SiO2, 19 wt % Al2O3∙SiO2). The infiltrated blocks were machined by different geometry tools in order to produce notched samples. The samples were loaded in three-point bending, and the loading force values were recorded against the cross-head displacements and the crack opening displacements. To measure up the notch sensitivity and toughness of the MMSFs, the fracture energies and the fracture toughness values were determined. The results showed that the mentioned quantities are needed to describe the behavior of MMSFs. The fracture energies were shown to be notch-sensitive, while the fracture toughness values were dependent only on the matrix material and were insensitive to the notch geometry. The complex investigation of the fracture surfaces revealed strong bonding between the hollow spheres and the Al99.5 matrix due to a chemical reaction, while this bonding was found to be weaker in the case of the AlSi12 matrix. This difference resulted in completely different crack propagation modes in the case of the different matrices.

Highlights

Metal matrix syntactic foams (MMSFs) or composite metal foams (CMFs) are foams with high specific strength
metal matrix syntactic foams (MMSFs) showed elastic-plastic fracture behavior; besides the measurement of the fracture energies, the R-curve approach is suggested for investigating the toughness of MMSFs
The fracture energy up to the maximal force values and the critical value of the J-integral are both necessary to judge the toughness of the MMSFs

Summary

Introduction

Metal matrix syntactic foams (MMSFs) or composite metal foams (CMFs) are foams with high specific strength. In MMSFs the incorporated porosities—necessary for a foam structure—are ensured by low wall thickness hollow spheres. This structure leads to higher relative density (~0.5) foams exhibiting outstanding compressive properties compared at least to the “conventional” open and/or closed cell metallic foams. Most of the above mentioned studies deals with the room temperature compressive properties of MMSFs, but efforts have been made to map their properties at cryogenic and elevated temperatures [33,56,57,58,59]

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