T1075/T1095 Questions 1

[ziggywiggy]

I have an application where a piece of high carbon T1075 and/or T1095 spring steel is bent over a portion of a 10 inch radius to achieve a cantilever spring. See attached link below.

Question 1: I can use either a 1.5 inch wide 0.125 or an 11 inch wide 0.062 to achieve the same spring rate. Which one will have the longer life span and/or most cycles?

Question 2: What are the consequences of stacking the 0.062 to achieve an even higher spring rate? Abrasion? Premature failure?

http://www.realestateinlasvegas.com/T1075.htm

Much THANKS!

 

[sbozy25]

Well, you can manipulate your fatigue life to what ever you want on either one depending on how it is manufactured. There are post-processing steps that can be done to increase or decrease your life.

I would say your best bet would to contact a company and tell them what sort of life you would like to get.

Also, The idea of stacking is bad. I would not reccomend it, you will run into many issues some of which you listed.

I am not sure what all companies out there could make it. However, I just quoted a job very similar (it was similar in aplication, but made from stainless).

http://www.mw-ind.com

Check out the website, and you might find a way to go from there.

 

[ziggywiggy]

THANKS for your feedback!

Having a VERY tough time finding answers. Not familiar with an "post-processing" other than the obvious annealing/rolling/tempering/quenching/carbonizing. Are you talking about the addition of other metals to create an alloy?

I've contacted about 10 steel distributors and manufacturers and NONE of them had the faintest idea how to answer these questions.

I've revised the webpage to explain the application in more detail. From what I can tell, this would be an EXCELLENT question for a metallurgy course final exam at some university.

 

[desertfox]

Hi ziggywiggy

I think I may be able to help,but first I need some more info:- firstly

is it required that the springs return to the position shown
after the weight is removed?

Whereabouts on the spring are you placing the weight and
what deflection do you require?

I can see the possibility of making a shaped spring to achieve what you require but I think the loads your talking
about and deflection are to much for the sections your quoting.

regards

desertfox

 

[ziggywiggy]

Thanks for responding DF. I've revised my webpage with more detail regarding the application. Please visit:

http://www.realestateinlasvegas.com/T1075.htm

for more info.

In answer to your questions:

1) Yes, the spring is attached to the arch on the left side of the image and is bent over the arch to come down on the right side. As such, when the above-weight is removed the spring returns to it's straight position as shown in the images.

2) The springs have rollers attached to the free end (right side) which allows for them to contact and travel underneath a horizontal plane which moves up and down on the spring. A simple cantilever spring with a deflection of 11 inches.

All dimensions are at the above-mentioned webpage.

I've already built a working model using both sizes of springs, am just wondering which spring will have a longer life span/more cycles. In other words, will a thick 0.125" T1075 cantilever spring last longer than a thinner 0.062" T1075 cantilver spring or the other way around?

Thanks for your help.

 

[sbozy25]

Well how long do you need the part to last? That is the biggest question. Then, once you know that, develop a DVPR and cycle test the parts. The best data you could ever get is that which you generate, not so much what we tell you. The blue tempered 1095 you mentioned in the webpage is a higher grade of materil, but with higher grades comes higher price. 1075 is relatively standard and will be most cost efficient for you.

By processing I mean, how hard you take the part, do you polish edges to take down stress concentrators, any fatigue peening, etc. There are many things that can be done to boost life. It all depends on what you want.

 

[israelkk]

From the

http://www.realestateinlasvegas.com/T1075.htm

web page I see three issues.

1. 11" deflection of an 18" cantilever beam is considered large deflection. Therefore, it doesn't follow the standard (linear) cantilever beam formulations.

2. When the beam starts to deflects it touches the 10" radius therefore, the active beam length is no longer 18" It is gradually decreases. The more deflection the shorter the beam becomes. Therefore, the stresses at the beam increase progressively. The force - deflection curve will be highly nonlinear.

3. The 0.062" thick 11' wide beam is more likely a plate than a beam. I see a practical problem how to evenly apply the load on the 11" long tip. If the force will not be evenly distributed the beam will tend to deflect in torsion added to the bending deflection.

Only an exact analysis can give the answers to your questions and give the stresses in the springs which will allow fatigue analysis.

Linear analysis of the two beams (as simple cantilever beams) give only a force of 38.3lb for the 0.062" thick beam and only a force of 42.8 lb for the 0.125" thick beam to receive the 11" deflection, assuming the force applied at the tip of the beam.

However, as I mentioned previously this is a large deflection case and to complicate it more, the beam length progressively decreases at it touches the 10" round base and the force and stresses progressively increase.

http://israelkk.googlepages.com/home

 

[ziggywiggy]

WOW, excellent response Israelkk! I impressed with your evaluation. I hadn't thought of the beam, in essence, decreasing in length due to it's contact with the radius - makes perfect sense.

Also, your calculations are right on with mine (F = 3DEI/L3rd) as well as with the empirical date derived from the invention.

In regards to the force applied to the "beam" or plate, I've attached several rollers along the free edge over a 1" long x 11"wide metal plate that crosses the last inch of the free edge to try and keep torsional forces to a minimum.

Question: When I spoke with Admiral Steel, they told me that all of their high carbon steel is stored and shipped via tightly wound coils with an ID of 20 inches. If contact with the radius does in fact significantly increase the stress and consequently fatigue on the "beam", wouldn't the coils that such material is stored and shipped in also cause such increased fatigue? Thanks again for your help!

 

[israelkk]

When you wound the strip over a mandrel with diameter large such as 20" which is 160 times larger that then 0.125" thickness there is a stress in the strip but it not large enough to create a significant permanent set in the strip. This is only a one cycle stress therefore, there is no chance for fatigue failure.

In your design the issue is not just that it is bend over the 10" base which may induce a one time permanent set in the 0.125" strip. The problem is that when part of the beam comes in contact with the base it is no longer part of the cantilever beam because it can no longer deflect more. Therefore, the actual beam length is shorter than 18" and the beam spring rate increases. The result is that the stress in the beam increases too. The force needed to continue the deflection has to grow. Therefore, when the deflection reaches 11" the force will be much larger than the calculated force (~40lb).

 

[ziggywiggy]

Questions: Is there a known ratio of bend/thickness for T1075 that is acceptable? A ratio that will allow the spring to flex with a reasonable number of cycles (2000 min) and no premature fatigue failure?

If those number of cycles simply cannot be achieved with T1075, is there another similarly priced metal that you might recommend? Thank you.

 

[NickE]

ziggywiggy- thats not how fatigue data is normally calculated.


normally I calculate the peak stresses. Then compare with a published S-N curve for the material. My suppliers provide data on fluctuating (double bend) endurance limit at 5% failure rate.

EG: 7C27Mo2 from Sandvik has an endurance limit of 760MPa+/-760MPa


Nick
I love materials science!

 

[ziggywiggy]

Any idea where I can find the S-N curve for T1075 steel? None of the steel companies that I've called have a clue. Thanks.

 

[sbozy25]

Well my machine design book from college has 1 in there for 1075, but if I were you I would contact a material supplier and ask them. It is a fairly common steel, so you should not have much of a problem finding a supplier.

 

[ziggywiggy]

Any chance someone has the T1075 data/curve from the ASM Handbook Vol. #1 that they could email? Also, I've revised the webpage significantly. Please take a look and advise on other potential metals/alloys that might work.

Of course, ALL help is greatly appreciated!

http://www.realestateinlasvegas.com/Cantilever.htm

 

[NickE]

I have to tell you I don't have data for regular grades of spring steels, the ultra clean versions produced for high fatigue life are different. I am pretty sure you are going to be in a high stress low cycle regime, at that, surface condition and residual stresses are going to dominate fatigue life.

I second the recommendation of testing, particularly important if the environment is not clean dry air.

 

[ziggywiggy]

Motion passed . . . I'm going to build a testing device and will post data with picts when finished. Thanks again for everyone's help!