When 3:30 PM - 5:00 PM Feb 01, 2008
Where 1670 CSE
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Stephen Harris, General Motors

Micro-Raman Spectroscopy to Determine the Full State of Stress of Silicon. Application to Eutectic Si Particles in Cast Al

Micro-Raman spectroscopy has been widely used to measure local stresses in silicon and other materials. However, a single (scalar) line position measurement cannot determine the complete stress state unless the stress is already known to have a very simple (1-parameter) form, such as uniaxial or hydrostatic. We describe new Raman experiments that take advantage of polarization, intensity, and frequency information. These experiments allow us to determine the full state of stress at the surface of silicon wafers under load. The experimentally measured values for sxx, syy, and txy are in good agreement with those calculated from ABAQUS models. Combining Raman and finite element techniques, we examine several eutectic silicon particles in cast Al and measure residual stresses. We then make in-situ measurements of the rate of stress buildup in these particles due to load transfer from the Al matrix during tensile deformation. It is the fracture of eutectic Si particles that leads to the ductile failure of the cast Al. Our results are being used as input to a micromechanics code being developed to predict the ductility of cast Al.