When analysing a plastic material for a plate, what value should I input into the plastic material specification when only given a stress vs strain graph  see fig A attached with no strain value which only show a yield stress of 60 MPa?

Other properties given are as a homogenous elastic material, the elastic modulus is 69300 and poison ration of 0.3.

and i would like to analyse the developement of plastic zone within the plate if it assumed to be a plastic material. with 5 MPa increment from 20 MPa to 40 MPa.