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The top photograph shows how the two helical cracks have joined together
and initiated a rapid fracture process that caused the final failure of
the bolt.
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The lower photograph is a region of this surface at higher magnification.
It shows both ductile and cleavage fracture surfaces as well as regions
in which inclusions have been pulled out of one side of the crack.
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Fracture behavior of this type terminated the life of the associated equipment
after only 18 hours. The typical period for wave activity suggests that
the sample experienced about 10,000 tensile stress cycles that exceeded
the yield stress before failing. |
