Freecad won't show you if it break.
From a material point of view, you're modeling a very simple material behaviour : linear elasticity.
It means that the stress rises lineary when the strain increases. The slope of this beahoviour law is the Young modulus you entered.
In your FEM calculation, you never gave a "max strain" or "max stress" value. So FC won't know it for you.
In your case, you have to know when the linear behaviour ends.
If you look this picture :
(taken from here : https://en.wikipedia.org/wiki/Stress%E2 ... rain_curve
Your model is valid if you stay in the first linear part of the curve (in blue). If you excess (for your material) this area, you're simulation will be meaningless.
So, in your documentation, perhaps you have a linear elasticity limit ?
If you find a stress or strain limit, you'll have to look on your results to see if you've passed this limit or not.