DOI: 10.1002/adem.200600039 In-situ High-resolution X-ray CT Observation of Compressive and Damage Behaviour of Aluminium Foams by Local Tomography Technique** By Tomomi Ohgaki,* Hiroyuki Toda, Masakazu Kobayashi, Kentaro Uesugi, Toshiro Kobayashi, Mitsuo Niinomi, Toshikazu Akahori, Koichi Makii and Yasuhiro Aruga Cellular aluminium foams exhibits complicated struc- tures. [1,2] The 3D analysis is therefore of crucial importance in order to improve mechanical performance of such foams. Re- cently, outstanding energy absorption has been increased on foams for protection impact on lightweight vehicles. 3D microstructures such as micropores and foaming agents in aluminium foams have been visualized and quanti- tatively evaluated by synchrotron X-ray tomography. [3] Due to limited field of view for the high-resolution synchrotron X-ray CT, a local tomography technique has been applied for in-situ experiments. The local tomography is a method to ob- serve only a region of interest (ROI) in a sample that is larger than the size of X-ray beam, [4,5] providing a unique possibility to realize the in-situ mechanical experiments at high resolu- tion. [3] In order to evaluate the elastic and plastic compressive be- haviour of the foams, a local strain mapping technique by tracking microstructural features was applied. [3,6–8] In the pre- vious studies, it was found that locally inhomogeneous strain distribution was measured attributed to the existence of coarse pores. [3] However, in those studies, number of markers was limited (several hundred-points); the adequate spatial densities of strain points were not obtained to see the effects of microstructure by the 3D local strain mapping. The aim of this study was to investigate the compressive and damage behaviour of aluminium foams. Using the local tomography technique and an in-situ test rig, the relations be- tween microstructural features and fracture behaviour were assessed by the 3D local strain mapping. Results: Figure 2 shows 3D rendered perspective views of tomographic data, representing micropores and particle dis- tribution superposed to the surface contours of the cell wall (a) before and (b) after compression up to nominal strain of 10 %. The yellow features indicate the micropore distribution and the red features indicate the particle distribution. The number of the micropores and the particles in this image are 7856 and 1177, respectively (Since the pores with an equiva- lent diameter under two voxels are considered too small, they were rejected for the analysis.) There are three large micro- pores in the centre in Figure 2(a). During the compression, the crack was initiated from one large micropore, which was connected to the surface of the cell. Because the stress concen- trates to larger micropores from which micro-cracks were ini- tiated. In Figure 2(b), the crack was initiated at the upper right of the cell wall and the cell wall might be bent due to the compressive load. Figure 3(a) shows the histograms of the micropore size in the CT scanned regions and those from which the micro- cracks were initiated in the six different regions. The number of the CT scanned regions is 10 for the histograms including the other similar samples. The number of the micropores in COMMUNICATIONS ADVANCED ENGINEERING MATERIALS 2006, 8, No. 6 © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim http://www.aem-journal.com 473 – [*] Dr. T. Ohgaki, Dr. H. Toda, Dr. M. Kobayashi, Dr. T. Kobayashi, Prof. M. Niinomi, Dr. T. Akahori Department of Production Systems Engineering Toyohashi University of Technology 1-1 Hibarigaoka, Tempaku-cho, Toyohashi 441-8580 (Japan) E-mail: ohgaki@tutpse.tut.ac.jp K. Uesugi Japan Synchrotron Radiation Research Institute 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan) Dr. K. Makii, Y. Aruga Materials Research Laboratory Kobe Steel, Ltd. 1-5-5 Takatsukadai, Nishi-ku, Kobe, Hyogo 651-2271 (Japan) [**] The synchrotron radiation experiments were performed at the BL20B2 and the BL47XU in the SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal Nos. 2003B0292-NM-np, 2003B0293-NM-np-Na, 2004A0356-CM-np, 2004A0358-CM-np-Na, and 2004B0457- NI-np). This work is supported by the New Energy and Indus- trial Technology Development Organization (NEDO) as Col- laborative Research of Production and Fabrication Technology Development of Aluminium useful for Automobile Light- weighting. Fig. 1. (a) Diagram of local tomography. (b) The regions of interest in the aluminium foam sample scanned by the local tomography technique.