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Re: A325 Bolts

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I was involved in a project where that was done.  As I remember, the
bolts were snapping and breaking, but I don't remember what the failure
mechanism was (tension, shear, etc.).  The contractor ended up welding
the connections.
If the bolts were indeed 'snapping and breaking' rather than stretching inelastically, the failure mode was brittle fracture in tension. It's easy to spot: the fracture surface is granular and there's no noticeable permanent deformation. At one time 'crystallization' was blamed for the failure, and every so often you still hear people using that term.

Without more details it's hard to diagnose just what was doing it. Brittle behavior can cause a bolt to fracture during installation if the fastener is tightened past the yield stress. Insufficient pre- load can also lead to failure if the applied load exceeds the bolt preload. In that case the ultimate cause of failure is low cycle fatigue brought on by yielding at a point of stress concentration.

Welding may not be the cure. Substandard welds are notorious for starting fractures. You really do need to be careful when you start doing stuff like this before you know what the original problem is.

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw/



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