Contents lists available at ScienceDirect Mechanics of Materials journal homepage: www.elsevier.com/locate/mechmat Low cycle fatigue behaviour of closed-cell aluminium foam M. Ulbin a , S. Glodež a, ⁎ , M. Vesenjak a , I. Duarte b , B. Podgornik c , Z. Ren a , J. Kramberger a a University of Maribor, Faculty of Mechanical Engineering, Smetanova 17, 2000 Maribor, Slovenia b University of Aveiro, Department of Mechanical Engineering, Centre for Mechanical Technology and Automation, TEMA, Campus Universitario de Santiago, 3810-193 Aveiro, Portugal c Institute of Metals and Technology, Lepi pot 11, 1000 Ljubljana, Slovenia ARTICLEINFO Keywords: Aluminium foams Micro Computed Tomography (μCT) Fatigue behaviour Numerical analysis Experiments ABSTRACT The computational and experimental investigation of the fatigue behaviour of AlSi7 aluminium foam is pre- sented in this study. The internal structure of a highly porous specimen was recorded using CT images to enable the subsequent detailed numerical modelling using the finite element method. A new approach for determina- tionofthefatiguelifeoffoammaterialswasdeveloped,wherethestandardisedapproachisverydifficultoreven not possible to be used. In the proposed approach, several numerical models with different porosity were built and analysed instead of the numerical model, with real porosity of an actual porous structure. Stress-strain results obtained by the numerical analyses of these models were then used in the subsequent fatigue analysis to determine the fatigue lives of the treated porous specimens. Numerical results were compared with the ex- perimental results, which were performed using low cycle fatigue testing under oscillating tensile loading with stress ratio R =0.1. The developed approach enables the fatigue analyses and prediction of the fatigue lives of various porous structures where a real numerical model is very difficult to build because of its very complicated internal structure. 1. Introduction Generally, metal foams are materials with low densities and novel physical, mechanical, thermal, and acoustic properties (Ashby et al., 2000; Taherishargh et al., 2017; Pinto et al., 2011; Banhart, 2001). These materials present a unique opportunity for adopting in light- weight structures, energy absorption, thermal management, etc. As presented in (Shen et al., 2006; Simoneau et al., 2016), porous metals can be used advantageously for the replacement of damaged bones. Foaming the metal, i.e. introducing voids in the microstructure, de- creases the density and increases the apparent thickness. A number of distinctprocess-routeshavebeendevelopedtomakemetalfoams.Some of them produce open-cell foams, and others produce foams in which the majority of cells are closed. Applications may at first be highly specialised, but, as commercial material production volume increases and costs decrease, widespread adoption of steel foams becomes pos- sible (Smith et al., 2012; Fiedler et al., 2015). Basically the properties of a foam are defined by the base material (steel, aluminium, etc.) of which it is made, its relative density (relation between the foam density, ρ, and density of the solid material, ρ s ), and by pore morphology and topology (Redenbach, 2009; Altenbach and Öchsner, 2010; Szlancsik et al., 2015). It is possible for foams with identical relative densities to have differing cellular structure, which could influence the behaviour and properties of treated foam sig- nificantly (Vesenjak et al., 2010). Metal foams can also be classified according to their porosity, or the number of cells (pores) that exist per unit length. The porosity can either be calculated from measured den- sity of a porous specimen and the density of the base material, or computed from scanned images by multiplying the number of voxels representing pores with the volume of a single voxel. Foams with the same relative density but a larger number of pores per unit length will contain ligaments with smaller cross-sections, as a greater number of pores and, thus, more ligaments, will exist. In addition to being light, non-flammable and recyclable, the closed-cell metal foams exhibit a high specific strength and good impact energy absorption under com- pressive loading. These multifunctional materials, in particular closed- cell Al-alloy foams, are being used or tested as light structural materials in building (e.g. cladding), equipment (e.g. good vibration and noise absorbers), cars (e.g. impact energy absorbers), helicopters, airplanes and ships (Lehmhus et al., 2013). They are usually incorporated in hollow structures (Duarte et al., 2015a,b,c, 2014) or sandwich panels (Banhart and Seeliger, 2008). In almost all of the aforementioned applications, these materials are subjected to a complex combination of monotonic and cyclic loads. https://doi.org/10.1016/j.mechmat.2019.03.014 Received 25 January 2019; Received in revised form 21 March 2019 ⁎ Corresponding author. E-mail address: srecko.glodez@um.si (S. Glodež). Mechanics of Materials 133 (2019) 165–173 Available online 22 March 2019 0167-6636/ © 2019 Published by Elsevier Ltd. T