ı just found this " Cold-roll steel shear strength is approximately 80% of its tensile strength.". I could not find anything else.
it is the ratio of shear stress to yield stress
if it is equal to one the material slid
According to von Misses plasticity theory a value of Y/3^0.5 (square root of 3) is a good approximation of the shear strength of a metal with tensile strength Y.
This is the general form for all metals.
Do we have the coefficient we use for only steels ?
Steels are a very wide family of iron alloys; if you use a specific steel type (and hardening condition) you may be able to find a better estimate.
In this case, (ultimate) tensile strength (UTS), as determined by a tensile test, is greater than yield strength (YS) about 40 ~ 60%.
The tensile yield strength (tYS) is double the value of shear yield strength (sYS) at 45° ( tYS=2xsYS), or the shear yield strength is the half the value of yield strength: sYS = tYS/2.
We can see this senario easly in a Mohr´s circle, ploted considering the tensile test stress state condictions. This relation can be used for each TRUE EFFECTIVE tensile stress during all the tensile test.
But, if we are think on ENGINEERING (ultimate) tensile strength (UTS), this relation is no longer valid, because the important reduction in real area after exceeded yield stress.
The TRUE maximum stress (TMS), that a ductile steel can support (as a cold rolled one), is bigger than the engineering one (TMS > UTS), even considering the effective stress, estimated by the Bridgman correction for hoop stress.
Therefore, for a cold rolled steel, as cited in your question, a typical YS is about 190 MPa; UTS is about 300 MPa, the true maximum effective stress (TMS) is about 480 MPa (hoop correction considered) and its maximum shear stress (MSS) is about 240 MPa (the half of TMS: 480/2 = 240 MPa). Note that MSS = 80% UTS !
I made myself a graph for better visualize what I describe above.
I hope I have been useful.
Willy Ank.
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