The methodology for fracture analysis of polymeric composites with scanning electron microscopes (SEM) is still under discussion. Many authors prefer to use sputter coating with a conductive material instead of applying low-voltage (LV) or variable-pressure (VP) methods, which preserves the original surfaces. The present work examines the effects of sputter coating with 25 nm of gold on the topography of carbon-epoxy composites fracture surfaces, using an atomic force microscope. Also, the influence of SEM imaging parameters on fractal measurements is evaluated for the VP-SEM and LV-SEM methods. It was observed that topographic measurements were not significantly affected by the gold coating at tested scale. Moreover, changes on SEM setup leads to nonlinear outcome on texture parameters, such as fractal dimension and entropy values. For VP-SEM or LV-SEM, fractal dimension and entropy values did not present any evident relation with image quality parameters, but the resolution must be optimized with imaging setup, accompanied by charge neutralization.

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In this work, NIH ImageJ plugins for extended depth-from-focus reconstructions (EDFR) based on spatial domain operations were compared and tested for usage optimization. Also, some preprocessing solutions for light microscopy image stacks were evaluated, suggesting a general routine for the ImageJ user to get reliable elevation maps from grayscale image stacks. Two reflected light microscope image stacks were used to test the EDFR plugins: one bright-field image stack for the fracture of carbon-epoxy composite and its darkfield corresponding stack at same (x,y,z) spatial coordinates. Image quality analysis consisted of the comparison of signal-to-noise ratio and resolution parameters with the consistence of elevation maps, based on roughness and fractal measurements. Darkfield illumination contributed to enhance the homogeneity of images in stack and resulting height maps, reducing the influence of digital image processing choices on the dispersion of topographic measurements. The subtract background filter, as a preprocessing tool, contributed to produce sharper focused images. In general, the increasing of kernel size for EDFR spatial domain-based solutions will produce smooth height maps. Finally, this work has the main objective to establish suitable guidelines to generate elevation maps by light microscopy.

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Correlative fractography is a new expression proposed here to describe a new method for the association between scanning electron microscopy~SEM! and light microscopy~LM! for the qualitative and quantitative analysis of fracture surfaces. This article presents a new method involving the fusion of one elevation map obtained by extended depth from focus reconstruction from LM with exactly the same area by SEM and associated techniques, as X-ray mapping. The true topographic information is perfectly associated to local fracture mechanisms with this new technique, presented here as an alternative to stereo-pair reconstruction for the investigation of fractured components. The great advantage of this technique resides in the possibility of combining any imaging methods associated with LM and SEM for the same observed field from fracture surface.

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