hi, there!

I have read a "Manual for LS-DYNA Wood Material Model 143"(website: http://www.tfhrc.gov/safety/pubs/04097/sec150.htm#toc_1_5_1 and http://www.tfhrc.gov/safety/pubs/04097/append_e.htm).

I have two question:

1. how to calculate the consistency parameter (formula (180)) by potential function, I'm quite not understant how the formula (19), (20), (25), and (26) came out. Could anyone explain it to me or tell me what material I should get and read?

If someone knows of books/articles dealing with the meaning of the concept of potential in physics (or concerning the physical bases underlying the energy methods of mechanics) then I would very much appreciate getting to know about these.