The effect of morphological imperfections on damage in 3D FE analysis of open-cell metal foam core sandwich panels

A 3D FE model of an open-cell aluminium alloy metal foam core sandwich panel subject to uniform compression has been created in ABAQUS to study the effect of varying the foam strut aspect ratio on the elastic properties of the core. A continuum viscoplastic damage model, previously calibrated using microtensile test data for the aluminium alloy’s optimally aged condition in conjunction with X-ray micro-tomography scans of the undeformed struts, was implemented through the user defined subroutine VUMAT. In addition, FE models of the open-cell metal foam core sandwich panel subject to three point and four point bending were produced in accordance with ASTM C-393-00, hence providing a virtual standardised test to assess the foam core elastic properties. These FE models used a tabulated elastic–plastic material model and were employed to verify the implementation of the damage model in the uniform compression FE simulations. The effect of two different types of morphological imperfections – fractured cell walls and missing cells – on the mechanical properties of the foam core was studied for uniform compression. The effect of these imperfections on the extent of visible structural damage of the foam core was studied for indentation loading scenarios indicative of an accidental tool strike under ground repair conditions, which is one important design consideration for potential alternative airplane wing skin materials. The effect of varying the indenter radius on the extent of visible structural damage was also considered so as to capture the influence of varying angles of tool drop impact. The Young’s modulus and shear strength of the foam core experienced a significant knock-down effect under the presence of both fractured cell walls and missing cells. The extent of visible structural damage was largely unaffected by either type of defect or by varying the indenter radius.