example is depicted in Fig. 6. On the higher length scale, the cell structure, only few weaker cells show larger deformations (see Fig. 1). With increasing load a fracture process zone develops in front of the notch root, which contains localised plastic yielding and micro cracking. At about 80% of the peak load a main crack starts from the notch root to propagate through the foam structure. This is accompanied by building of crack bridges up to 1 - 3 cell sizes behind the crack tip and by micro cracking of cell walls in the FPZ (see Fig. 6). The crack follows the path of lowest fracture resistance, which is in general the path with the thinnest cell walls. CONCLUSION Standard fracture mechanic tests based on the stress intensity factor, the J-integral and the COD concept were performed on ALPORAS® aluminium foams with different densities. Additionally, in-situ fracture tests in the SEM and local surface deformation measurements were carried out. The surface strain measurements reveal a very localised deformation of the foam on different length scales. During the crack growth a large fracture process zone develops, which contains localised plastic yielding and micro cracking of several cell walls. Due to the very small linear elastic part in the load versus load line displacement curve no valid KIC values according to ASTM E399 could be obtained. Although all performed J-integral tests were valid, the standard determination of fracture toughness values in terms of an initial J-value is not useful. The ASTM standards are optimised for solid metals and their application to ductile metallic foams is usually not possible and they should be adapted to the special properties of the foams. It was found that measurements of crack opening displacement in terms of COD5 gives a better approach to useful fracture toughness values. ACKNOWLEDGEMENT The financial support by the Austrian Fonds zur Förderung der wissenschaftlichen Forschung and of the Österreichischen Nationalbankfonds (Project P13231PHY/FWF535) is gratefully acknowledged. REFERENCES 1. H. Bart-Smith, A.-F. Bastawros, D. R. Mumm, A. G. Evans, D. J. Sypeck, H. N. G. Wadley, (1998) Acta Mater. 46, 10, 3583-3592 2. H. Fusheng, Z. Zhengang, G. Junchang, (1998) Metall. and Mat. Trans. 29A, 2497-2502 3. R. Gradinger, F. G. Rammerstorfer, (1999) Acta Mater. 47, 1, 143-148 4. E. Andrews, W. Sanders, L.J. Gibson, (1999) Mat. Science and Eng. A270, 113-124 5. Y. Sugimura, J. Meyer, M.Y. He, H. Bart-Smith, J. Grenstedt, A.G. Evans, (1997) Acta Mater. 45, 12, 5245-5259 6. O.B. Olurin, N.A. Fleck, M.F. Ashby, (2000) Mat. Science and Eng. A291, 136-146 7. C. Motz, R. Pippan, Proc. ECF13, M. Fuentes, M. Elices, A. Martin-Meizoso & J.M. MartinezEsnaola, Eds., Elsevier Sciences (2000), 160c1.pdf (CDROM), 1-8 8. T. Miyoshi, M. Itoh, S. Akiyama, A. Kitahara, (2000) Adv. Eng. Materials 2, No. 4, 179-183 9. K.Y.G. McCullough, N.A. Fleck, M.F. Ashby, (1999) Acta Mater. 47, 2331-2343 10. A. Tatschl (2000), Neue experimentelle Methoden zur Charakterisierung von Verformungsvorgängen, Ph.D. thesis, University of Leoben, Austria 11. K.H. Schwalbe, A. Cornec, Fatigue of Eng. Mat. (1991), 14, 405-412
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