Plotting Stress Strain Curve

Thanks for the question. Looking at the equation for epsilon.t and sigma t, a value of zero sigma t should yield a value of zero epsilon.t. If I just define sigma t as zero, I am in fact getting epsilon.t as zero as it should be. However when I define a set of values for sigma t from zero, it doesn't give me epsilon.t values starting from zero. 

Thanks again for looking into this.