Why are the hardness of studs and bolts slightly higher than that of nuts?
Thread Content
Why are the hardness of studs and bolts slightly higher than that of nuts?
When the relative strengths of the bolt and nut materials are nearly equal, as the axial load increases, the threads of the bolt and nut bend, the nut expands more, and the effective shear area of the two threads decreases. If thread stripping occurs, it is difficult to determine whether the bolt or the nut fails first. If the material strength of the bolt is **higher than that of the nut (which is the case for most bolt/nut assemblies), the bolt threads will not gradually twist, and the thread profile of the nut will remain undeformed, even if the yield strength of the nut material is very low. If thread stripping failure occurs under these conditions, the nut threads will clearly unscrew within the cylindrical surface formed by the major diameter of the bolt threads. Similarly, when the material strength of the nut is greater than that of the bolt, the bending and twisting of the bolt’s threads are controlled by the nut’s threads. If the assembly fails due to thread stripping, the stripping of the bolt threads occurs on the cylindrical surface generated by the minor diameter of the nut threads. Generally speaking, the closer the material strengths of the bolt and nut to each other, the lower the probability of thread stripping failure, regardless of which one fails first. If the strengths are inconsistent, the failure load will be slightly higher. This is why nuts tested with hardened mandrels exhibit a slightly higher failure load compared to those tested with bolts of equal strength. The above text explains why the hardness of studs and bolts is slightly higher than that of nuts. The text is from the Internet: http://www.360doc.com/content/090112/14/9722_2316991.html This post was last edited by www557 on 2009-3-9 at 16:00.]
The main factor is still wear.
What was said on the 2nd floor is very correct. I used to think the same way: nuts are cheaper than bolts, so it’s better to choose those that are easier to machine in order to cause damage