Questions regarding maximum yield strength for standard hardened steel dowel pins

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Hello everyone,

I would like to ask if anyone could please help me with the following
situation.

I am using a standard hardened steel "pull out" dowel pin from
www.mcmaster.com as a bearing shaft. I need to know the maximum load
the dowel / shaft can support without taking a permanent set and/or
becoming permanently deformed or bent. I need the shaft to always
spring back to its original position after the load is removed.

I emailed Mcmaster, but they were not able to give the maximum Yield
strength of the dowels.

Does hardening increase the maximum Yield stress? If so, is there a way
to calculate or estimate how hardening affects the yield stress ? If I
know the yield stress, then I can compare the maximum yield to the
bending stress given by my beam design program, and I think this will
tell me if the dowel can support the load without taking a set.

Here is what Mcmaster said about the dowels and material...

"Hardened Steel- Made from hardened steel such as C1541, or 4037 and
4140 alloy steel. Core Rockwell hardness is C47-C58 (surface hardness
is RC 60). Shear strength is the amount of force that the side of a pin
can withstand before breaking. Single shear strength is the amount of
force applied against a fastener in one place causing the fastener to
break into two pieces. Single shear strength is 130,000 psi.  An
internally threaded tapped hole in one end of these pins lets you pull
them out with a removal screw or a threaded puller such as 92330A (see
page 3083 ) and reuse them. All meet ASME B18.8.2. Length tolerance is
=B1.010"."

I would appreciate any advice or suggestions on how I can get a close
estimate on this, and what would be a reasonable safety factor to
apply. Nobody could get hurt if the device fails, but I just need it to
be reliable. I have to consider several factors when choosing a shaft
size, and everything fits in a tight space.

There are tradeoffs and space constraints when going to a bigger shaft,
so I need to know how to estimate this in order to make the best
compromise. It's desirable to use the smallest shaft diameter possible,
that will support the load with a reasonable safety factor & not take a
set.

Thanks for your help.
John


Re: Questions regarding maximum yield strength for standard hardened steel dowel pins
John2005 wrote:
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Make sure that the loads never get very close to yielding the shaft, if
you only knew the yield strength of this catalog article.

Quoted text here. Click to load it


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.

---------------------------------------------------------------------

Good luck.

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


--
1) Eat Till SATISFIED, Not STUFFED... Atkins repeated 9 times in the book
2) Exercise: It's Non-Negotiable..... Chapter 22 title, Atkins book
We've slightly trimmed the long signature. Click to see the full one.
Re: Questions regarding maximum yield strength for standard hardened steel dowel pins
jbuch wrote:
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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

Re: Questions regarding maximum yield strength for standard hardened steel dowel pins
Michael Dahms wrote:
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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.

--
1) Eat Till SATISFIED, Not STUFFED... Atkins repeated 9 times in the book
2) Exercise: It's Non-Negotiable..... Chapter 22 title, Atkins book
We've slightly trimmed the long signature. Click to see the full one.
Re: Questions regarding maximum yield strength for standard hardened steel dowel pins
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


Re: Questions regarding maximum yield strength for standard hardened steel dowel pins
jbuch wrote:
Quoted text here. Click to load it

Thanks! Might be interesting to try a test.

Michael Dahms

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