Can someone either give me a good explanation of this or link me to a site that can? Thanks.
This may help.
I'm left wondering whether you're after polycrystalline models for yielding (and if so, of what "type and degree" or an overall view of the different approaches available) or mechanistic explanations?
the latter, please.
Let's see if these are a step in the right direction.
The polycrystalline part of this lecture series:
This has a short intro about polycrystalline slip:
A pretty interesting one although focuses primarily on twinning:
General topic related stuff:
Separate names with a comma.