steel tear-out strength?

[jklingel]

This may be too technical for this forum, but here goes, as some of you folks are likely engineers (??). Can anyone give me a reference for how to calculate the tear-out strength of mild steel, or a forum where I can ask? (I asked a question on an engineering forum once and was quickly informed that the forum was not for mere mortals.) This assumes, of course, that there is not a ton of prerequisite knowledge I need to learn beforehand. Specifically, I have a 1" OD pin in a 3/4" mild steel plate, and the center of the pin's hole is approx 1 1/8" from the edge of the steel plate. That pin will be pulled at various angles by a clevis-ended hydraulic cylinder. Obviously, the weak spot is when the pin only has 5/8" of meat around it. How would one calculate how many tons I can put on that pin before she tears out? I am assuming that the pin's shear strength will exceed the tear-out strength, but if that is not the case, let me know. Shear strength I can calculate. Thanks. john. PS: I was told that 3/4" mild steel has something like a 74,000 pound-feet tear strength, but that does not mean much to me. I know what lb-f are, but how/where/when does that apply to my situation?

 

[A_Pmech]

A basic approximation of the force required to tear out the pin can be arrived at by multiplying the distance from the hole center to the plate edge parallel to the action of the force times two times the thickness times the shear strength of the plate.

Ref:

http://www.eng-tips.com/viewthread.cfm?qid=96156&page=1

Any book on steel design will cover this in greater detail, including basic design practices such as recommended minimum distances from the edge of the plate for various diameter pins. I would suggest a study of available publications on the subject.

 

[jklingel]

AP: Thanks! If I read your post right, that is (.625) (2)(.75)(shear strength) = lbs of load. Correct? I will look up the shear of MS and read the article you cited in the morning; gotta hit the sack. john

 

[A_Pmech]

Hi John,

Taking your hypothetical example and the formula provided in the link...

Given:

Distance from the center of the pin to the edge of the plate: 1.125"

Plate thickness: .75"

Shear strength of steels is .75 times the tensile strength. Assuming A36 plate having a tensile strength of 60,000 PSI, that gives a shear strength of 45,000 PSI.

The formula becomes:

1.125 * 2 * .75 * 45,000 = Tearout Force

75,900lbs = Tearout Force

Don't take my word or the word of anyone else on the internet though. Read a decent steel design manual and thoroughly acquaint yourself with the mathematics before you go building anything.

P.S. I'm not an engineer and I don't play one on TV.

 

[CraigFL]

There are other things that may govern the strength of this connection such as the bearing pressure of the pin on the steel hole or any bending forces which may cause the plate to bend.

 

[bchee]

P.S. I'm not an engineer and I don't play one on TV.

Have you ever stayed at a Holiday Inn Express?

 

[jklingel]

AP: Thanks. After seeing your numbers, I re-read your first post and realized I misread in my haste. I used the dist from the EDGE of the plate to CL. Oops. Read twice, measure 3 times, then cut. Yes, this will be "typical" 60K psi tensile steel. BTW: Your number is not far off what an engineer told me, but I got no explanation as to whence cometh said number. So I think your are spot on.
Craig: Thanks for pointing that out. There won't be any bending, not for this aspect, as the cylinder will be pulling the grapple arm up. Bending could happen later, when the cyl pushes it down; my design, which mimics commercial grapples, takes that into consideration... I hope. Time will tell.

 

[jklingel]

BTW: For anyone following this who wonders why the pin diameter is not considered here, pls see the link AP provided. Another caveat is that the distance from the edge to the center of the pin should be at least 1.5x the diameter of the pin. Ahhh. Now it all makes sense.

 

[A_Pmech]

John,

Glad to be of help.

CraigFL makes a good point about other parts of the connection that may be worth analyzing, which was part of my reason for recommending that you study a steel construction manual. It will outline procedures for analyzing various connection types to ensure you don't "miss a step".

I think you'll find that the compressive strength of the steel plate may be the limiting factor of the connection as-designed. The pin hole may begin to plastically deform due to compressive forces before the pin tears out of the plate.

 

[jklingel]

Thanks again. I will try to find that casual reference you suggested; I do this kind of thing all the time, and operate on a wing and a prayer. So far, so good. I pick up the hydraulic cylinders today, and their clevises may allow a thicker plate, too. And, I may be able to move the hole a tad deeper into the plate. Plastic? Hard to think of steel failing "plastically", but I understand what is said. Man's puny little forces, and subsequent frame of reference, are not a good judge of what happens when machines work things over.