Undergraduate experiment with fractal diffraction gratings

We present a simple diffraction experiment with fractal gratings based on the triadic Cantor set. Diffraction by fractals is proposed as a motivating strategy for students of optics in the potential applications of optical processing. Fraunhofer diffraction patterns are obtained using standard equipment present in most undergraduate physics laboratories and compared with those obtained with conventional periodic gratings. It is shown that fractal gratings produce self-similar diffraction patterns which can be evaluated analytically. Good agreement is obtained between experimental and numerical results. © 2011 IOP Publishing Ltd.We acknowledge financial support from grants DPI2008-02953 and TRA2009-0215, Ministerio de Ciencia e Innovacion, Spain. We also acknowledge support from Generalitat Valenciana through the project PROMETEO2009-077. This work has been developed by Teaching Innovation Groups from the Universitat Politecnica de Valencia (e-MACAFI) and the Universitat de Valencia (GCID35/2009).Monsoriu Serra, JA.; Furlan, WD.; Pons, A.; Gimenez Valentin, MH. (2011). Undergraduate experiment with fractal diffraction gratings. European Journal of Physics. 32:687-694. doi:10.1088/0143-0807/32/3/005S6876943

Effect of Titanium on the Mechanical Properties and Microstructure of Gray Cast Iron for Automotive Applications

Lamellar gray cast iron, with a mainly pearlitic microstructure, is widely used in the automotive industry, mostly in the manufacturing of brake disks. This work analyzes in depth the effects of small variations of titanium content on the microstructure and mechanical properties of cast iron brake disks. For this purpose, eight different heats of EN-GJL-250 cast iron were selected, with a similar chemical composition but with different titanium contents, varying from 0.013 to 0.031%. The drops in mechanical strength and hardness values measured on the high-Ti samples were correlated to microstructural variations quantitatively observed by means of optical and scanning electron microscope. It was found that titanium combines to form titanium nitrides, suppressing the beneficial microstructural effects of nitrogen at solidification. Residual nitrogen, if present in sufficient quantity, promotes the nucleation of primary austenite from the liquid and the formation of a fine microstructure, with small eutectic cells and lower graphite content. Such a microstructure provides brake disks with better mechanical properties. The interpretation of results was further supported by thermal analysis and thermodynamic calculations