Industry Confusion: Understanding Yield

Saturday, March 17th 2012

Misconceptions about yield are common, especially concerning studs. From our research in the field, we’ve found that 100% yield is often mistakenly used to refer stud breakage. In reality, 100% yield is a reference to the point that a stud passes from a plastic state to the elastic region of its load-bearing capabilities. This is also where the stud will not come back to its original length (by 0.2%).  Therefore if the stud is elongated past number 3 (as seen below) Hooke’s Law does not apply.

Stress-Strain Curve

For assemblers, this means that if you take the stud past 100% yield, the amount of load will not be directly proportionate to the length and stud load is uncertain. Even though failure isn’t guaranteed, your joint can easily leak. Most pressure vessels are very dynamic joints and taking them to yield, combined with temperature/pressure changes, can easily break the stud.