In-situ Micro-tensile Testing and X-ray Micro-tomography based FE Modeling of Open-cell Metal Foam Struts and Sandwich Panels

Microtensile testing was used to determine the mechanical properties of individual aluminium alloy open- cell foam struts. Finite element (FE) modelling of as-tested struts was carried out using X-ray microtomography (XMT) scans of the undeformed struts to define the geometry. Strut deformation was described by continuum viscoplastic damage constitutive equations calibrated by the microtensile test data for the aluminium alloy's optimally aged condition. The as-tested strut FE model was used to develop a procedure that compensates for the effect of grip slippage inherent in the microtensile testing of metal foam struts, which results in a considerable underestimation of the elastic stiffness. The calibrated constitutive equations were then implemented into 3D FE models of open-cell metal foam core sandwich panels to study the effect of varying the strut aspect ratio on the mechanical properties of the core under uniform compression, as well as core damage visibility under localised impact scenarios. An optimal strut aspect ratio was identified through simulation that provides the greatest energy absorption per unit mass whilst ensuring core damage is accurately reflected by face sheet deformation, which is necessary for detection and repair. FE models of the panel subject to three and four point bending were created to provide a virtual standardised test to assess the core elastic properties.