Fatigue properties of metal matrix syntactic foams

Orbulov, Imre Norbert and Katona, Bálint and Szebényi, Gábor (2014) Fatigue properties of metal matrix syntactic foams. In: Proceedings of Cellular Materials, CellMAT 2014, 2014.10.22-2014.10.24, Dresden.

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Abstract

Closed cell, high strength metallic foams, like ceramic hollow sphere reinforced metal matrix syntactic foams are distinguished materials to build light structural parts. The applications can range from load bearing structures to vibration damping structural parts like machine beds, spindles etc. In the latter case the fatigue properties are necessary in order to conduct proper design calculations. Simple and hybrid metal matrix syntactic foams with Al99.5 or AlSi12 matrix, reinforced by 1.5 mm and/or 0.15 mm ceramic hollow spheres were produced by pressure infiltration technique. The hollow spheres were built up from alumina, silica and mullite and they were provided by Globomet GmbH. and Envirospheres Ltd. respectively. The fatigue tests were performed on a universal hydraulic testing machine under force control at different and lower loading levels (k=0.6…1, compared to the compressive strength of the actual foams). The cylindrical specimens were carefully lubricated and placed between polished plates incorporated in a four bar upsetting tool. The deformation of the specimens was measured by a strain gage as a function of cycles. The results showed that the metal matrix syntactic foams have exhibited fatigue limits, due to the high ceramic sphere content. The softer, more ductile Al99.5 matrix syntactic foams have higher fatigue strength and similarly, the larger hollow spheres could result in higher fatigue limits. The failure mechanism could be connected to the brittle fracture of ceramic spheres embedded in the ductile matrix. Light microscopy revealed the breakage of the spheres in a plane closing ~45°with the loading direction. Due to this microcracks appeared in the most stressed region. Subsequently the cracks were propagated continuously and finally the whole specimen fractured. The foams exhibited high damage tolerance and remained undamaged far from the crack plane.

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