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Bolt Grade Help

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Old Jun 20, 2013 | 06:31 AM
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SLV
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Originally Posted by latrobedyna
SLV i have just one ? please would a bolt that hard maybe a tad brittle for that kind a work? I recall using grade 8 bolts on high pressure hydraulic couplers and the shot would some times snap the heads right off.
Good question, and a subject a lot of people don't understand when talking bolt strength. Strength is a relative term because as strength increases in metals, elasticity decreases. Strong means brittle, not so strong means more-ductile.

The thing is, two fasteners with differing material but the same or similar strength properties may have vastly different modulus of elasticity ratings. In this case, I don't find an elasticity rating for the 12.9 bolts, but a typical "alloy" steel will be more ductile than carbon steel, which is naturally brittle. More than likely, the 12.9 bolt has similar or even more ductile properties compared to grade 8 fasteners, even though the strength properties are greater.

Regardless, a shock bolt mount is a shear application, which means that the main load on the fastener is across the shank as opposed to a tension application (head bolt for example) that has its main load pulling on the fastener head.
 
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