Fatigue with Stainless Steel Bolt
Fatigue with Stainless Steel Bolt
(OP)
We have a 5/16 SST hex head bolt that keeps failing because of fatigue at our plant. The bolt is a ASTM A593C. I can't remember how much increasing from a 5/16 to a 3/8 will increase the fatigue strength and I don't what hex head stainless steel bolts are available in higher strength.
Any thoughts?
Thanks
Any thoughts?
Thanks





RE: Fatigue with Stainless Steel Bolt
SST does not identify the stainless steel involved and the properties required.
ASTM A 593 does not designate a bolt material
ASTM A 593 -
SPECIFICATION FOR CHARPY V-NOTCH TESTING REQUIREMENTS FOR STEEL PLATES FOR PRESSURE VESSEL
http://www.welding-advisers.com/
RE: Fatigue with Stainless Steel Bolt
RE: Fatigue with Stainless Steel Bolt
The only benefit to be gained by going to a larger bolt diameter is the increase in load carrying capacity. However, an adequate preload is still required to avoid subjecting the bolt to fatigue.
RE: Fatigue with Stainless Steel Bolt
The nut used is a cadmium plated nut.
You bring up a good point. What would a good preload/torque be for bolt like this? I'm little hesitant about using a torque wrench with a stainless bolt because it's seems like they can gall and then give false readings with a torque wrench.
RE: Fatigue with Stainless Steel Bolt
same manufacturer? You might have inferior
bolts.
RE: Fatigue with Stainless Steel Bolt
RE: Fatigue with Stainless Steel Bolt
RE: Fatigue with Stainless Steel Bolt
RE: Fatigue with Stainless Steel Bolt
Nick
I love materials science!
RE: Fatigue with Stainless Steel Bolt
Regarding your question of a good preload, something around 75% to 100% of the proof load is a good start. Look up the ASTM standard to learn what is the proof load for your fastener.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Fatigue with Stainless Steel Bolt
the heads of the bolts on the neoprene side as
well as on the nylon side? I think I would
use 85 percent of the yield of the bolts as a
minimum if the neoprene and nylon can take the
bearing forces under the washers or head of
the bolts. How hard is the neoprene? It does
seem strange that by going to a larger bolt,
you are starting to have failures. Same number
of bolts?
RE: Fatigue with Stainless Steel Bolt
The cross section for the set up goes cadmimu plated nut, nylon, neoprene, 1/8" stainless sheet, then bolt head.
Like I said earlier I'm a little concerned with getting false readings with a torque wrench if the nut catches on the thread of the bolt. Is there any other methods for torquing?
Thanks
RE: Fatigue with Stainless Steel Bolt
5/8 or 1.67 times the 3/8 diameter.
If you would use a thick washer on
each side it would help to improve the
clamping length and may give you
better torque control and reduce the
strain in the bolts.
RE: Fatigue with Stainless Steel Bolt
I'm guessing that what's happening now is that when the bin shaker whacks the nylon, it's compressing the rubber enough to remove all or most of whatever preload has been applied, and the head is pushed away from the inner bin wall, where it's exposed to the corrodent on its underside. Corrosive environments do not improve the fatigue life of fasteners.
Torquing the nut to anywhere near bolt yield will just cause the rubber, and to a lesser extent the nylon, to ooze out from under the retaining washer/nut.
A larger bolt might actually help a little.
As might putting a stainless bushing around the bolt shank, through the nylon and rubber layers, so the bolt is compressing a stack comprising the bin wall, the bushing, and the retaining washer under the nut, and the compression of the nylon and rubber is limited by the bushing, which should be a hair shorter than the combined thickness of the rubber and nylon.
Are you sure there wasn't a bushing in the stackup when it left the factory?
Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA
RE: Fatigue with Stainless Steel Bolt
RE: Fatigue with Stainless Steel Bolt
RE: Fatigue with Stainless Steel Bolt
ASTM F593 is the most widely available. ASTM A193 is another spec you might look at as its availability is fair.
And Mike, I have been selling stainless bolts for 15 years now but I will never be able to look at them the same way after that ear wax remark
RE: Fatigue with Stainless Steel Bolt
I am not sure your original req. about strength increase 5/16 to 3/8 was answered. The stress area for 5/16 = 0.0524 sq.in., 3/8 = 0.0775 sq.in from Mach.Handbook. The ratio is 1.48 or 48% increase. That is significant and may explain the difference between this application and the ones in the other building.