Questions regarding maximum yield strength for standard hardened steel dowel pins

Make sure that the loads never get very close to yielding the shaft, if you only knew the yield strength of this catalog article.

You might be learning a good lesson here.

You picked a part from a catalog.

The catalog dealer tells you he doesn't know what material it will be made of.......

He tells you that the surface hardness is evidently fairly well known.

However, he tells you that the interior hardness can vary quite a lot.

Since there is an empirical correlation between ultimate strength and the hardness, you know that the untimate strength can vary a lot.

You can figure out how much the strength variation could be by google searching for "Correlation hardness ultimate strength rockwell c" meaning that you are looking for the correlation between ultimate tensile strength and the hardness as measured on the Rockwell "C" scale. You will be able to see that there is an enormous strength difference between Rockwell C47 hardness and C58 hardness.

You may therefore assume that the tensile strength will be equivalent to that of Rockwell C47 - at a minimum.

There is also an emperical correlation between hardness and yield strength, so you can repeat all of the above to give you an estimate of the yield strength of whatever alloy you end up with.

Remember, the manufacturer told you that you might get any of a number of alloys.

The lesson I would take away is to not buy a "part" and then use it for a different purpose than intended.... unless I had some way to become assured of the minimum mechanical properties of the "part" so one could do an analysis.

Without having the properties of the part, analysis might not be very meaningful.

A number of people make bearing shafts for various purposes, and maybe that is the way to go. At least the catalog from a bearing shaft outfit might have the appropriate bearing shaft data.

-------------------------------------------------------------------- I can imagine a way to use a metallic zipper as a sort of continuous switch.

I wouldn't expect to get much help from the zipper industry with my questions on the electrical characteristics of zippers..... because the zipper industry makes fasteners, not electrical switches.

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Good luck.

I would approach the problem using the bearing shaft catalogs first and foremost.

AFAIK there is a correlation between hardness and ultimate tensile strenght for steels with a certain plastic deformability. For hardened steels, it is difficult to measure tensile strength, because fracture is flaw-controlled here. Just curious: Did you ever carry out a tensile test using a C58-hardness-specimen?

Unfortunately, I don't have the standards in my actual office, but I rememeber that the correlation between hardness an UTS is valid only up to a certain maximum hardness.

Michael Dahms

The old chart I am looking at for the correlation tops out at Rockwell C of 59 with an UTS of 329 Ksi or 232 kg/mm2.

There is at least one such copy you can google to pretty quick.

I have probably conducted just as many tensile tests using a C58 hardness specimen as the fellow raising the question.

Hi everyone,

Thanks for your feedback.

Here is some feedback I got from another forum, if it's possible to find the maximum yield stress by knowing the shear strength, this may allow me to get an estimate without worrying so much about the material (at least I hope). The shear strength is almost always given for dowels in catalogs ...

"israelkk (Aerospace)

1 Mar 06 19:09 If the shear strength is 130,000 psi then the tensile strength is 130000/0.577=225000 psi which is approximately in agreement with the C47 core hardness. At this strength the yield stress is close to the ultimate tensile strength and is is at least 90% of the ultimate tensile strength. This gives ~200000 psi. Safety factor to use depends for what purpose it is used. For aerospace use the factor will be 1.5 to brake."

israelkk (Aerospace)

2 Mar 06 7:35 The theoretical ratio between the ultimate shear strength to the ultimate tensile strength is 0.577. Therefore, if the pin/shaft spec gives the minimum shear strength then you can use this formula to calculate the ultimate tensile strength. However, the relation between the yield stress and the ultimate stress depends on the heat treatment. I estimated the 90% due to the 47RC. Anyway, since the pins are case hardened the outer diameter is much stronger than the core therefore you are on the safe side. On the other hand the pins may be too brittle.

Dowel pins are designed for shear/double shear use and not for bending. For bending I would prefer a custom made and properly heat treated shaft where the properties can be guarantied and verified using tensile test specimens.

CoryPad (Materials)

2 Mar 06 8:08 israelkk provided a good first step, but his information is slightly incorrect.

The 0.577 factor is the relationship between shear yield stress and tensile yield stress according to the von Mises/distortion energy/octahedral shear stress criterion. This criterion has been found to be suitable for nearly all crystalline metals.

The relationship between ultimate shear stress (the value provided by McMaster-Carr) and ultimate tensile stress varies from one material to another, but it is usually near 0.6.

israelkk's 0.9 factor for the ratio between tensile yield stress and ultimate tensile stress is accurate for hardened steels similar to yours. His advice regarding brittleness should be heeded, and so should his advice regarding using a real shaft made for this purpose rather than using a shear pin from a catalog.

Regards,

Cory

Thanks! Might be interesting to try a test.

Michael Dahms