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10.1 Introduction
Aluminium foams are ultra-light, multi-functional materials, which have been used
widely in various engineering applications, such as sandwich construction and
energy absorption. In the last 20 years, the compressive behaviour of foams has
been studied by means of macro measurement and phenomenological mechanical
models based on idealised cell geometries [
1
,
2
]. However, the meso-scale
mechanisms determining the compressive strength have not been completely
understood due to the complexity of the cell structures and their deformation.
Recent advances in X-ray computed tomography (CT) enable the non-
destructive characterisation of the meso-structure and deformation behaviour of a
foam using synchrotron [
3
] and laboratory X-ray sources [
4
]. The advantage of CT
is its capability to capture the internal structure and deformation of a material in
three dimensions (3D). However, one limitation of applying this technique during
in situ loading is that the test usually has to be interrupted at certain loading stages
to allow X-ray scanning. This may introduce stress relaxation and other effects. To
overcome this, continuous X-ray CT scanning is used in this study. Moreover,
improvements in meshing techniques and the upgrade of computational hardware
enable realistic simulations using finite element models (FEM) based on 3D CT
images [
5
]. Such image-based modelling can be applied to isolate the effects of
specific physical factors, e.g. cell-wall material properties [
6
] and strain rate [
7
], as
well as geometrical structural effects. It also can be used to infer the material
properties of cell walls using inverse methods [
8
]. The combination of X-ray
in situ CT experiments and image-based modelling can provide detailed infor-
mation for both qualitative and quantitative analyses.
This work aims at investigating the low-strain-rate compression of a closed-cell
aluminium foam by in situ X-ray testing and image-based modelling. First, in situ
compression was undertaken during which 3D CT images of the original and
successive deformed configurations of the foam were obtained. Then the CT image
of the original foam was used as the geometrical basis for a 3D FEM for simu-
lation. The experimental result delineates the deformation mechanism and its
effect on the stress-strain relationship of the foam. The numerical prediction
provides additional information, e.g. plastic strain distribution in the cell walls.
10.2 Experiment and Modelling
A cylindrical specimen was mechanically cut from a panel of the closed-cell
aluminium Alporas
TM
foam for the in situ compression experiment. The diameter
and thickness of the specimen are 20 and 10 mm, respectively. The specimen was
scanned using a Nikon Metris CT system housed in a customised bay at the Henry
Moseley X-ray Imaging Facility (HMXIF, Manchester, UK), which is capable of
fast data acquisition useful for minimising blurring during in situ experiments.
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