The influence of the fracture surface fractal dimension DF and the fractal dimension of grain microstructure DM on the strength of AISI 316L type austenitic stainless steel through the Hall-Petch relation has been studied. The change in complexity experimented by the net of grains, as measured by DM, is translated into the respective fracture surface irregularity through DF, in such a way that the higher the grain size (lower DM values) the lower the fracture surface roughness (lower values of DF) and the shallower the dimples on the fractured surfaces. The material was heat-treated at 904, 1010, 1095, and 1194°C, in order to develop equiaxed grain microstructures and then fractured by tension at room temperature. The fracture surfaces were analyzed with a scanning electron microscope, DF was determined using the slit-island method, and the values of DM were taken from the literature. The relation between grain size, DM, mechanical properties, and DF, developed for AISI 316L steel, could be generalized and therefore applied to most of the common micrograined metal alloys currently used in many key engineering areas.

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Stress corrosion cracking has been a problem in aluminum alloys exposed to an aggressive environment under high static residual tensile stress. This work is concerned with the application of electron microscopy to investigate possible causes that led to failure through stress corrosion cracking in the aluminum alloy 5182. This alloy is commonly used for making carbonated beverage containers. The containers in this study did not experience any problem at the time of the filling. However, after humid storage periods going from a few days to a few weeks, leakage at the can ends was reported in many of them. These leaks developed from a failure referred to as aluminum can end blow out.Figure la shows an SEM micrograph of a cross section of the score imposed on the top of the can during manufacturing. The unscored metal below the score is broken when the ring or tab is pulled out during opening.

There have been several attempts to find a relation between the fractal morphology of the fracture surfaces and the mechanical properties of engineering materials., although the current resuls are inconclusive. If there are correlations between the fractal dimension and such properties, this parameter could be very useful to predict them and to improve the resistance to fracture. The main part of the investigations concerned with the fractal geometry and fracture behavior concentrate on the relations between roughness and fracture toughness . In the present work, the effects of thermal aging at 850°C on the fracture topography developed during the rupture in tension at room temperature of a 304 type stainless steel and their relation with the strength and ductility, were studied using the fractal geometry approach.