Question regarding Shear strength for tonnage calculations
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  1. #1
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    Default Question regarding Shear strength for tonnage calculations

    When calculating tonnage in a tool (e.g. Progressive die) you have to calculate for shearing, stripper force, & forming. The formula to calculate the shearing (Cutting) is PARIMITER(in.) x MATERIAL THICKNESS (in.) x SHEAR STRENGTH (Tons).
    But There are no published standard values for shear strength like there are with tensile and yield strengths. Therefor, as I understand it, the data is estimated as a percentage of the ultimate tensile strength of the material.
    My question is, what is this percentage? The only reason I am asking is because I have seen it in books and magazine articles and web sites anywhere from 55% to 85% It is all over the board depending on who you ask...So is there a standard for the actual percentage somewhere other than opinions?

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    A common rule of thumb I use is 0.6 times ultimate yield strength give you a pretty close number for shear strength for most materials.

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    +1 on .6, I used .5 for tinplate and sheet steel (really thin DWI stuff) weren’t far out
    Mark

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    often ultimate shear strengh is assumed to be 75% of ultimate tensile strenght and shear yield strengh as 60% of tensile yield strenght.

    the topic is muddy, because its not like they are two sides of the same coin. tensile is 1-dimensional, shear is a 3-dimensional situation. its clear how to measure tensile but there are different way to measure shear (e.g. supported at two points of one? ductile or brittle?). actually there is no tensile strenght at all, everything fails in shear.

    there is plenty of "engineering" data available, like how much force to punch a hole or how much to shear a bolt (here, interestingly, the tensile/shear ratio will depend on the diameter). also the supplier will be able to quote or publishes a number for steels where its relevant (like d2).




    "According to five theories of failures we have five different relationship between shear strength and yield strength.

    Assume, ratio of shear strength to yield strength as K

    1.Maximum principle stress theory: K = 1

    2.Maximum principle strain theory: K=0.77:

    3.Maximum strain energy theory: K=0.62

    4.Maximum distortion energy theory: K=0.577

    5.Maximum shear stress theory: K=0.5"

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    Bliss used to publish a booklet called Computations For Sheet-Metal Working Operations, that had both mathematical and empirical coverage of blanking, forming, drawing, etc. This used to be the go-to for many tool design engineers. Worth getting one of the later additions if you do a lot of that kind of stuff.

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    I think the die makers handbook by jerry arnold might have a good reference.

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    Gotta double down on the Bliss Computations advice above. In the back they have many pages with Log-Log scales where you use a rule to line up values & extract an answer for everything presswork. Attached:

    Near as I can tell their theoretical yield points coincide with published yield values in the ASM manuals.

    Good luck,
    Matt
    Attached Thumbnails Attached Thumbnails bliss_computationsa.jpg   bliss_computationsb.jpg   bliss_computationsc.jpg   bliss_computationsd.jpg   bliss_computationse.jpg  



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