Just recently we examined some test bars made from pc in our Sinterstation
that were cryogenically fractured and then placed under an SEM. We noticed
some unusual concentric circles where individual powder particles (or where
a group of particles had melted together) had fractured. These look like
stress circles, and they probably are, but as I understand it these circles
are normally observed in cases of fatigue rather than a single brittle
fracture. This implies that whatever caused these circles was already
present in the particles, rather than being a result of the fracturing.
Has anyone else come across this phenomena? Has anyone an explanation? I can
email some SEM pictures to anyone interested.
Dr Ian Gibson
Dept. Mechanical Engg.
University of Hong Kong
tel: +852 2859 7901
fax: +852 2858 5415
"Always remember you're unique, just like everyone else."
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