# Effective strain

Hi,

I need some help here. I'm an MEng Materials with no full background in engineering. So I'm in a bit over my head.

I'm trying to understand the concept of hydrostatic stresses and effective strain in connection to worn surfaces. I am told I just need to know the equations but then I'm a bit confused.

I'm trying understand how equivalent strain is calculated from the shear angle of the interface θ.

In other words how this equation came about

E (Z) = (square root of 3/3) * tan theta

Thanks.

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