Quote:
Originally Posted by dcdoug
Are there any bolt stress scenarios in which Grade 5 would be stronger than Grade 8, or is Grade 8 always stronger and you are just trying to decide whether Grade 5 is enough?
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doug,
I'm reaching a long way back to my college days, so cut me a little slack if I don't get all of this exactly right. Engineers consider many properties when evaluating the appropriateness of a metal for a particular job. Those properties include hardness, toughness and britlleness among others. Grade 5 bolts don't have as much tensile strength (resistance to pulling) as Grade 8, but they are typically tougher and less brittle than Grade 8. So, a Grade 8 bolt is better for an application that will not be exposed to continuous on and off stresses (fatigue) and needs to be as strong as possible for occasional stresses. But a Grade 5 bolt might be better for an application where fatigue is more of a concern. So, it's not as simple as saying Grade 8 is always better than Grade 5. Given the way seat belt bolts are used, I used Grade 8 in my car.