# Hall Petch Equation

1. Apr 15, 2016

### richard9678

What is the Hall Petch equation. When I Google (images) I get::

σy = σo + ky / √d

or

σy = σo + ky d1/2

In the first ky is divided by √d and in the second multiplied by √d.

The second equation is in a study book I have.

Am I making a math error? Thanks.

Last edited: Apr 15, 2016
2. Apr 16, 2016

### Ssnow

I saw from different references that is $\sigma_{y}= \sigma_{0}+k_{y}d^{-\frac{1}{2}}$

3. Apr 16, 2016

### richard9678

Yes, the minus sign should be there. :-)