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Posted by D Sherman [72.47.9.228] on Monday, May 02, 2011 at 03:08:16 :
In Reply to: Grade Eight Bolts posted by gmharris [71.105.178.157] on Sunday, May 01, 2011 at 23:01:15 :
I would have to look in my books, but I think the only specified difference is in ultimate tensile strength. The bending test is a good one, but if they were to fail in service it would probably be from fatigue due to vibration causing cracks to gradually grow. In a properly designed bolted joint, the engineer has to consider not just the tensile strength of the bolt, but its shear strength, the compressive and shear strength of the parts that it's holding together, relative to the direction of the load, and any vibration or shock loads. most of the time, bolts are stretched in shear (head bolts are the most obvious exception), and a bolt that's "too strong" in shear will cause the parts its holding to deform before the bolt fails. That's not an argument for using weak bolts, though, since the joint should have been designed with enough bolts and enough bearing area to carry the load without deforming the bolted parts.