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Registered
Join Date: Apr 2002
Location: Houston (Clearlake), TX
Posts: 11,310
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A dark area from slow crack growth could be from oxidation on the cracked surface along with the two opposite fracture surfaces fretting together and wearing away the beach marks, but that's not the case here.
I'd say the fatigue crack in this shaft grew pretty fast as evidenced by the relatively wide spacing on the beach marks by the key.
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2014 Cayman S (track rat w/GT4 suspension)
1979 930 (475 rwhp at 0.95 bar)
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