Where to find torsional strength of stainless steel varients 4

[jeffbiss]

Hello,

I'm brand new to this forum and am an electrical engineer. I have tried to locate information regarding torsional strengths of the various types of stainless steel and have had no luck.

When purchasing stainless steel shaft it would be nice to know what the torque limits are for each type and shaft diameter but no supplier seems to provide this information. So, can anyone provide me a source for this information? A book title or a web page would be very nice.

thanks in advance, Jeff

 

[unclesyd]

The number that I use for the Austenitic Stainless Steels is 40% of the UTS.

Any of the hardenable Stainless Steels I use 45% of the UTS value.

 

[CoryPad]

You need to specify your limit(s) to get a good answer.

Are you looking to avoid quasi-static torsional yield? Or long-term cylic yield? Or fracture due to torsion?

Shaft analysis (material independent) is documented in many places. Here are a couple:

http://www.utm.edu/departments/engin/lemaster/Machine Design/Lecture 18.pdf

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19840018973_1984018973.pdf

Regards,

Cory

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[jeffbiss]

unclesyd and CoryPad,

Thanks for your replies. Now to do more research.

unclesyd, I assume that you mean that if I locate torsional strength values for UTC steel and multiply it by 0.4 then I have the torsional value for unhardened stainless?

Therefore, it seems that stainless is weaker than whatever UTC steel is. I am trying to identify that now.

CoryPad, The PDFs are very good resources. It's been a while since I did mechanical analysis because I generally am doing electrical engineering. From reading I did this morning I believe that "yield" implies repeated use and failure versus single stress to failure test.

As I view torque strength, I was thinking that I need to know what the empirically derived torque limit is for a range of 303 stainless steel shaft diameters as determined by the manufacturer, because that is standard stock for sale, so I can purchase the appropriate diameter that they sell. I also assume that some sort of derating is required to ensure that failure does not occur in normal usage.

I thought that there are emipirically determined tables indicating the torque limits in this case, whichever it would be, similar to the electrical constraints presented in electrical component data sheets.

 

[unclesyd]

The numbers I gave are for use with the Ultimate Tensile Strength values.

What size shaft are you interested in as they are numerous shaft materials that are much better than 303 SS?

 

[EdStainless]

The torsional limit will be directly proportional to the UTS.
You will find that 303 has poor fatigue properties.

When I was making splined shafts we always tested both the ultimate load capacity and the fatigue limit (at much lower loads, usually 25%). In reality we usually ended up operating at 40-50% of the torsional YIELD value. We would twist a shaft and measure the force. We took the defection of the load vs rotation as yield.

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http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[jeffbiss]

unclesyd,

When I searched for UTS I got a bunch of results that were all over the map. Thanks for the definition. I just wasn't sure whether it was a standards organization acronym or not.

I am designing a therapeutic device and am currently mocking it up in wood with off-the-shelf parts from SDP-SI.com and when the thing looks like it is correct, I will make a proof of concept in metal.

I bought a worm and worm gear with a 0.1875 bore because the main diameters seemed to fit my concept of the device's overall size. I realized that I had no idea as to what the torque limit was of that size shaft or any size of any given material. SDP-SI sells precision shafts of a variety of diameters and materials (12L14 steel, 303/416/420 stainless, and C1060 steel).

So, I was looking for a means for determining which diameter shaft I should use, once I determine the torque that would be required, so that I could then purchase a new worm and worm gear if the ones I did buy were wrong for the correct shaft diameter.

 

[jeffbiss]

Alright, I've found that a table providing ultimate shaft failure limits does not exist. So, can anyone provide me a link to information or the title of a book about how to use hardness, or other attributes, to determine torsion failure limits? For example, the shaft is hardened to RC 26-32.

The NASA "Design of Power Transmitting Shafts" doesn't seem to deal with that type of material attribute. You mechanical engineers must have some resources that discuss material attributes for use in calculations.

 

[CoryPad]

You cannot design a shaft based on indentation hardness. In general, hardness has been used as a simple-to-obtain substitute for ultimate tensile strength. A proper design would require actual static and fatigue strength requirements. If you will be working in a simplified manner, then use a hardness-strength conversion table (Google will find many) and use the estimated strength in the equations shown in design guides like the NASA one.

Regards,

Cory

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