# Johnson Cook failure model

Hi

can Anyone help me to find johnson-cook failure model damage parameters(d1, d2, d3, d4) for Advanced hgih strength steels like DP and TRIP?

thanks

### Re: Johnson-Cook damage + DP and TRIP steels

"J-C strength
model constants for mild steel are A=217 MPa, B = 234 MPa, n = 0.643 and
C = 0.076 and for DP590 steel are A = 430 MPa, B = 824 MPa, n = 0.510
and C = 0.017".  You might try to contact the authors and see whether they have any experimental data on failure.  Then fit your own parameters.

Alternatively, look at  http://web.mit.edu/icl/AHSS_Technical_Aug_15%20_final_.pdf and use some of the data/references they have provided.

### thanks

have read the MIT proposal before but my problem is that there is no
failure parameter in papers for advanced high strength steels, and I
don't have experiment data to find them.

thanks for your attention and guides.

finding damage parameter need 3 tests(shear test, uniaxial tension test on notched and smooth specimen), so how can I get these parameter just by modeling not experiment?
is it possible or no? if it is possible with needs to less experiment test data, which tests are needed?

### More on Johnson-Cook damage

Why do you need a notched tensile test?  You will find such data very hard to come by for high strain rates and high temperatures.

Johnson-Cook damage model parameters are hard to find because they are often in the classified national lab literature.  You will have no choice but to fit your own parameters for most materials.  Even that is quite difficult because of the spread in failure strain data.

The Johnson-Cook damage model gives the plastic strain at failure as a function of the (mean stress/deviatoric stress), the plastic strain rate, and the temperature. See http://www.scribd.com/doc/6226594/em2004paper270 equation (20).  The three parameters D1, D2, D3 need tests under three known stress states.

If you want find these parameters numerically (without testing) then you'll have to do calculations based on the microstructure of the steel.  You will need fracture strengths of grain interfaces and bulk grains as a function of stress state.  If those fracture strengths are not available you'll have to go one step lower and try to compute them using molecular dynamics simulations.  These simulations will need the correct grain boundary potentials etc.  To find these potential you'll have to go down one more length scale (and most likely, time scale) and do some ab-initio calculations.

In my opinion it's easier to search for data in the literature and fit the parameters you need.

-- Biswajit

### find J-C model parameters numerically

Dear sir, Thanks for your wonderful explanation. I want to find the Johnson-Cook damage model parameters numerically, but don't know how. Could you recommend me some papers about it? Thank you very much in advance.

### johnson cook parameter of st 37

is that you can help me to download this thesis, I can not do it in my country.
« Numerical And Experimental Investigation Of Perforation Of St-37 Steel Plates By Oblique Impact » :

here is my email: ben2oeb@yahoo.fr
thank you

### Johnson Cook parameter

Hi

can Anyone help me to find johnson-cook failure model damage parameters(d1, d2, d3, d4) for modified 9Cr-1Mo steel?