ICF100591OR 2D AND 3D SELF-AFFINE CRACK PROPAGATION ON ALUMINUM ALLOYS M. Hinojosa, E. I. Morales, X. Guerrero, J. Aldaco and U. Ortiz Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, A.P. 076 Suc "F", Cd. Universitaria, San Nicolás de los Garza, N.L. MEXICO. ABSTRACT The self-affine exponents associated with the crack propagation phenomenon are evaluated on samples of aluminum alloys both on 2D and 3D experimental conditions. Fracture surfaces were generated by Charpy impact tests on samples of A319-type aluminum cast alloy. Roughness exponents and correlation length on the perpendicular and parallel directions with respect to the crack propagation direction were determined, this analysis was also performed for the arrested crack propagation front. In the two-dimensional case, cracks were propagated on notched tension specimens of aluminum foil and the resulting self-affine crack paths were recorded and analyzed, the self-affine parameters were determined for both longitudinal and perpendicular direction in order to investigate the effect of the microstructural anisotropy. Self-affine analysis was carried out using the Zmax variable bandwidth method. The combined use of different techniques (SEM, AFM, Optical microscopy and stylus profilometry) enabled the analysis over up to seven decades of length scales. The results are analyzed in terms of recent crack propagation models and the self-affine parameters are found to be correlated with microstructural characteristic lengths. KEYWORDS Roughness exponents, self-affine crack paths, fracture surfaces, aluminum alloys, crack propagation. INTRODUCTION Crack propagation and the fracture of materials are catastrophic phenomena of considerable scientific, technological an economical importance [1-4]. Despite the scale of the problem and the considerable effort that has been undertaken by engineers and scientists of different disciplines, there is at present no clear understanding of the fracture process. In recent years much interest has been devoted to the self-affine character of fracture surfaces and crack propagation [5-7]. The fractal nature of fracture surfaces was first quantitatively studied in the mid-eighties [8]. At about the same time it was suggested that the fracture of heterogeneous media has some universal properties similar to critical phase transitions [9]. Later, experimental evidence led to the conjecture of the existence of a universal roughness exponent [10] for the fracture surfaces of many different materials [11], though this is still a controversial topic [7,12]. Anyway, it is now clearly established that fracture surfaces are self-affine objects that can be quantitatively described by self-affine parameters like one or more roughness exponents and one or more characteristic lengths such as cut-off lengths separating different scaling regimes, and the correlation length.
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