My focus is on the analysis of fracture toughness of Al-Si alloys by using a Nanoidentation. is there anyone doing this aspect ?
I would be very surprised if you (or anyone) could generate any fracture at all in Al-Si alloys by nanoindentation, or even by higher-load indentation. And without producing fracture, you can't measure fracture toughness. Or am I missing the point here?
Si grains are capable of brittle transcrystalline fracture under indentation. The problem is that they have rod-like cross section and measuring the total length of cracks will be not trivial. Also this would not tell much about the fracture toughness of the alloy.
I agree with Prof. Roberts. You have to produce fracture to measure fracture toughness. I am not convinced that methods to estimate fracture toughness from Hertzian fracture in indentation will be reliable in Al-Si alloys, especially if you are using cast alloys, in which fracture properties, such as elongation, fatigue life, K1c, etc., are dictated by casting defects including entrained bifilms. These defects are not expected to affect the indentation properties, at least not to a great extent. Good luck!
I looked at the above reference with a high degree of cynicsim, but I went far enough to find the paper outlining this "fracture toughness of ductile materials via indentation" method:
J. Lee, J. Jang, B. Lee, Y. Choi, S.G. Lee, D. Kwon
An instrumented indentation technique for estimating fracture toughness of ductile materials: a critical indentation energy model based on continuum damage mechanics
Acta Materialia, 54 (4) (2006), pp. 1101–1109
It actually looks fairly believncle - especially as these authors present not just numerical results but micrographs showing void formation beneath the (spherical) indenter. So this technique is probably worth following up.
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