The fracture strength of Si particles in tensile specimens of Sr-modified A356 castings

Griffiths, J.; Oliver, E. C.; Fitzpatrick, M. E.; Finlayson, T.; Viano, D. and Wang, Q. (2007). The fracture strength of Si particles in tensile specimens of Sr-modified A356 castings. In: Crepeau, Paul N.; Tiryakioğlu, Murat and Campbell, John eds. Shape Casting: 2nd International Symposium. Warrendale, PA: TMS (The Minerals, Metals and Materials Society), pp. 127–134.

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Abstract

Neutron diffraction methods have been successfully used to measure the stress in the eutectic silicon particles in a casting as a function of the applied tensile strain at all strains up to fracture. These measurements have been made for four microstructural conditions – fine and coarse secondary dendrite arm spacings and low and high yield stresses. We have identified and characterized the three classic components of particle stress (i) the thermal misfit stress, resulting from mismatch in the coefficients of thermal expansion, (ii) the elastic misfit stress, resulting from differences in the elastic constants, and (iii) the plasticity misfit stress, resulting from the plastically inhomogeneous nature of the silicon and aluminum constituents of the casting. We have estimated a lower limit to the fracture strength of the silicon particles and suggest possible explanations for its value.

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