Textural Analysis of Fatique Crack Surfaces: Image Pre-processing

For the fatique crack history reconstitution, new methods of quantitative microfractography are beeing developed based on the image processing and textural analysis. SEM magnifications between micro- and macrofractography are used. Two image pre-processing operatins were suggested and proved to prepare the crack surface images for analytical treatment: 1. Normalization is used to transform the image to a stationary form. Compared to the generally used equalization, it conserves the shape of brightness distribution and saves the character of the texture. 2. Binarization is used to transform the grayscale image to a system of thick fibres. An objective criterion for the threshold brightness value was found as that resulting into the maximum number of objects. Both methods were succesfully applied together with the following textural analysis

Comparison of bayesian and other approaches to the estimation of fatigue crack growth rate from 2D textural features

The fatigue crack growth rate can be explained using features of the surface of a structure. Among other methods, linear regression can be used to explain crack growth velocity. Nonlinear transformations of fracture surface texture features may be useful as explanatory variables. Nonetheless, the number of derived explanatory variables increases very quickly, and it is very important to select only few of the best performing ones and prevent overfitting at the same time. To perform selection of the explanatory variables, it is necessary to assess quality of the given sub-model. We use fractographic data to study performance of different information criteria and statistical tests as means of the sub-model quality measurement. Furthermore, to address overfitting, we provide recommendations based on a cross-validation analysis. Among other conclusions, we suggest the Bayesian Information Criterion, which favours sub-models fitting the data considerably well and does not lose the capability to generalize at the same time

Effect of Si and Fe on the Recrystallization Response of Al-Mn Alloys with Zr Addition

Al-Mn alloys are often used for the production of automotive heat exchanger fins. During brazing at about 600°C, recrystallization and grain coarsening resulting in the reduction of the strength and possible buckling of the fin can occur. In order to obtain a good recrystallization resistance, the alloy should contain a dense and homogeneous distribution of second phase particles. The effect of Si and Fe addition on the recrystallization response of Al-Mn-Zr alloys direct-chill cast in the laboratory conditions and twin-roll cast in the industrial conditions was examined. Microstructure of the alloys was characterized during downstream processing. The particles were analyzed by light metallography, energy dispersive X-ray spectroscopy and by means of electron backscattering diffraction. Computer assisted quantitative particle analysis was carried out on field emission gun-scanning electron microscope micrographs. Vickers hardness and electrical conductivity were measured at thicker sheets, while at the final gauge of 65 μm the 0.2% proof stress was evaluated. The best recrystallization resistance had twin-roll cast alloy containing 0.5 wt% Si and 0.2 wt% Fe

Effect of Si and Fe on the Recrystallization Response of Al-Mn Alloys with Zr Addition

Al-Mn alloys are often used for the production of automotive heat exchanger fins. During brazing at about 600°C, recrystallization and grain coarsening resulting in the reduction of the strength and possible buckling of the fin can occur. In order to obtain a good recrystallization resistance, the alloy should contain a dense and homogeneous distribution of second phase particles. The effect of Si and Fe addition on the recrystallization response of Al-Mn-Zr alloys direct-chill cast in the laboratory conditions and twin-roll cast in the industrial conditions was examined. Microstructure of the alloys was characterized during downstream processing. The particles were analyzed by light metallography, energy dispersive X-ray spectroscopy and by means of electron backscattering diffraction. Computer assisted quantitative particle analysis was carried out on field emission gun-scanning electron microscope micrographs. Vickers hardness and electrical conductivity were measured at thicker sheets, while at the final gauge of 65 μm the 0.2% proof stress was evaluated. The best recrystallization resistance had twin-roll cast alloy containing 0.5 wt% Si and 0.2 wt% Fe