Torque values are calculated with how much safety factor below the yield point?

Torque values are calculated with how much safety factor below the yield point?

• A. 10%
• B. 30%
• C. 20%
• D. 50%

Answer: (B)

The concept being tested is using an elastic safety margin for fastener preload. Torque values are chosen so the bolt clamping force stays well below the yield strength, keeping the bolt in the elastic range. The typical rule of thumb is about 30% below yield, meaning you aim for a preload that corresponds to roughly 70% of the material’s yield strength. This margin accounts for variations in friction on threads and under the bolt head, lubrication differences, temperature changes, and manufacturing tolerances, so the bolt won’t yield during operation and will return to its original length when torque is removed. A smaller margin like 10% or 20% would be riskier because it leaves less room for those factors before plastic deformation could occur; a larger margin like 50% would reduce the clamping force unnecessarily and isn’t the standard practice for automotive fasteners.

The concept being tested is using an elastic safety margin for fastener preload. Torque values are chosen so the bolt clamping force stays well below the yield strength, keeping the bolt in the elastic range. The typical rule of thumb is about 30% below yield, meaning you aim for a preload that corresponds to roughly 70% of the material’s yield strength. This margin accounts for variations in friction on threads and under the bolt head, lubrication differences, temperature changes, and manufacturing tolerances, so the bolt won’t yield during operation and will return to its original length when torque is removed. A smaller margin like 10% or 20% would be riskier because it leaves less room for those factors before plastic deformation could occur; a larger margin like 50% would reduce the clamping force unnecessarily and isn’t the standard practice for automotive fasteners.