The possible role of microstructural features in determining the self-affinity of the fracture surface of a cast aluminum alloy is explored in this work. Fracture surfaces generated both in tension and impact tests were topometrically analyzed by atomic force microscopy, scanning electron microscopy, and stylus profilometry. The roughness exponent exhibited the “universal” value ζ ≈ 0.78, and the correlation length ζ was of the order of the grain size. The brittle intermetallic compounds known to be important in crack initiation did not show any correlation with the self-affine parameters of the resulting fracture surfaces in this particular case.
The long distance roughness of the fracture surface of a dendritic aluminum alloy is studied over a wide range of length scales. Self-affinity analysis was performed over samples broken in Charpy impact tests. Simultaneous use of Atomic Force Microscopy, SEM and stylus profilometry allowed us to cover a wide spectrum of length scales, spanning over seven decades, from a few nanometers up to one centimeter. The roughness exponent and correlation length were obtained using the variable bandwidth method. For the roughness exponent, a value of 0.8 was obtained, corresponding to the reported universal exponent. Correlation length was found to correspond well to the characteristic length of the largest heterogeneities in the complex microstructure. Our results provide information that can help to improve our understanding of the role of microstructural parameters on crack propagation mechanisms.
In this work we report the fractographic study of polymer matrix composites specimens reinforced with glass and carbon fibers. Specimens of a polyester matrix composite with 30% of E-glass fibers are prepared and fractured in flexure mode. We also test an epoxy matrix composite with 30% carbon fibers, which is fractured in flexure mode. All specimens are manufactured based on the D790 ASTM standard for bending mode at room temperature. As an exception, the composites with epoxy matrix and reinforced with carbon fiber are cured in an autoclave. The most commonly observed fracture mechanisms are debonding in the interphase, delamination, Chevron lines, microbuckling, river patterns and radial fracture on the fibers.
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