For this material the c.d.f. is given by $$F\left(\Xi\right)=1-\beta-\left(1-\beta\right)\frac{\alpha}{\Xi}\left(1-e^{-\Xi/\alpha}\right)\,.$$ Note that $$\lim\limits _{\Xi\to\infty}F\left(\Xi\right)=1-\beta$$ represents the maximum allowable damage. Therefore, $\beta$ regulates the maximum allowable damage, whereas $\alpha$ controls the rate at which $F\left(\Xi\right)$ increases with increasing $\Xi$ .

Example:

<damage type="CDF Simo">
  <a>0.1</a>
  <b>0</b>
  <Dmax>1</Dmax>
</damage>