Abstract
Realistic simulations are increasingly demanded to clarify the dynamic behaviour of foam materials, because, on one hand, the significant variability (e.g. 20% scatter band) of foam properties and the lack of reliable dynamic test methods for foams bring particular difficulty to accurately evaluate the strain-rate sensitivity in experiments; while on the other hand numerical models based on idealised cell structures (e.g. Kelvin and Voronoi) may not be sufficiently representative to capture the actual structural effect. To overcome these limitations, the strain-rate sensitivity of the compressive and tensile properties of closed-cell aluminium Alporas foam is investigated in this study by means of meso-scale realistic finite element (FE) simulations. The FE modelling method based on X-ray computed tomography (CT) image is introduced first, as well as its applications to foam materials. Then the compression and tension of Alporas foam at a wide variety of applied nominal strain-rates are simulated using FE model constructed from the actual cell geometry obtained from the CT image. The stain-rate sensitivity of compressive strength (collapse stress) and tensile strength (0.2% offset yield point) are evaluated when considering different cell-wall material properties. The numerical results show that the rate dependence of cell-wall material is the main cause of the strain-rate hardening of the compressive and tensile strengths at low and intermediate strain-rates. When the strain-rate is sufficiently high, shock compression is initiated, which significantly enhances the stress at the loading end and has complicated effect on the stress at the supporting end. The plastic tensile wave effect is evident at high strain-rates, but shock tension cannot develop in Alporas foam due to the softening associated with single fracture process zone occurring in tensile response. In all cases the micro inertia of individual cell walls subjected to localised deformation is found to have negligible effect on the macro strain-rate sensitivity of Alporas foam.
Highlights
Aluminium foams possess unique properties, which are attractive for various engineering applications such as energy absorption and sandwich construction
Three-dimensional geometrically realistic finite element (FE) model based on computed tomography (CT) image has been developed to investigate the strain-rate effect on the dynamic properties of closedcell aluminium foam (Alporas)
Uniaxial compression and tension have been simulated at different nominal strainrates (1 × 10−3 − 3 × 103 s−1)
Summary
Aluminium foams possess unique properties, which are attractive for various engineering applications such as energy absorption and sandwich construction. Their compressive properties are of particular importance when they are used to absorb energy and attenuate impact/blast loads. The understanding of their tensile strength is important for the design of load-bearing structures (e.g. sandwich structures). Under dynamic loading, their cell deformation may be distinct from the one under quasistatic loading, contributing to macroscopic strain-rate effect. The actual causes of strain-rate effect have not been completely recognised
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