ORAL REFERENCE: ICF100438OR FRACTURE TOUGHNESS AND FRACTURE PROCESSES IN DUCTILE METALLIC FOAMS C. Motz and R. Pippan Erich Schmid Institute of Material Science, Austrian Academy of Sciences, A-8700 Leoben, Austria ABSTRACT For structural applications of aluminium foams, besides tensile and compressive behaviour, fatigue and energy absorbing the fracture mechanic behaviour is important. Fracture mechanic tests were performed on compact tension (CT) specimens of sizes from W=50 mm to W=300 mm made of ALPORAS® foams with different densities. In addition to standard tests, in-situ fracture experiments in a scanning electron microscope were performed. Besides the load and the load line displacement also crack extension via a potential drop technique, crack tip opening displacement and local deformations were measured. The deformation is strongly localized on different length scales. In front of the notch root a fracture process zone with concentrated deformation develops. The crack propagates through the foam building many secondary cracks and crack bridges. The determination of fracture toughness values in terms of stress intensity factor K, J-integral and crack tip opening displacement is discussed. The comparison of the K vs. ∆a (crack extension), J vs. ∆a and COD vs. ∆a with the actual fracture processes at the crack tip and load displacement response reveals that COD5 gives the most reliable values to characterize the fracture toughness. The critical values for COD5 range from 0.35 mm to 1.0 mm depending on the relative density of the foam. KEYWORDS metallic foams, cellular solids, fracture toughness, fracture processes, local deformation. INTRODUCTION In the last few years metallic foams, e.g. made of aluminium or magnesium alloys, have become commercially available due to improvements in the manufacturing processes. This new class of materials exhibits partly unusual mechanical properties compared to common metals. For successful design of load bearing structural elements, besides the well-investigated compression and energy absorbing behaviour [14], also the fracture behaviour and fracture toughness values are needed. Until now only a limited number of publications [5-7] addressing this topic are available. The aim of this investigation is to provide a closer look at fracture processes and the determination of fracture toughness values for these foams. Thus, standard fracture mechanic tests and additionally in-situ fracture tests in the scanning electron microscope were performed do determine fracture processes and fracture toughness values. For the tests, an ALPORAS® aluminium foam, which is commercially available, with different densities was used. Standard fracture mechanic parameters, like stress intensity factor K, J-integral and crack opening displacement COD, were
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