Formula for bending a rod in the elastic range

[pistorinoj]

Is there a formula to calculate the radius that a rod of a given radius can be bent around while staying in the elastic range?

For example, if I had a rod that was 1/4" in diameter and made of HDPE (which I think has a modulus of elasticity of 0.8 GPa), how would I calculate the minimum radius the rod could be bent around while still staying in the elastic range so that it could be unwound without deformation?

 

[sophiecentaur]

I think the answer to your question would need more information than just the modulus.

<Moderator's note: removed advice to post in ME after moving the thread to ME.>