VUMAT subroutine based on the 2016 article by Fangxin Hu, Gang Shi and Yongjiu Shi

[Generation237]

Hi,
i am new here and i would like to present you the difficulties that i have been facing. I have now been trying for quite a few weeks without success to use the constitutive model presented in the attached article below (link to this article is also below) to write a VUMAT subroutine. My main problems with this implementation come from implementing equation 63 - 70. Do you guys have any idea on how to write this VUMAT subroutine?
Any help is very much needed and will be welcomed.

Link to the article:

https://sci-hub.ru/https://doi.org/10.1016/j.engstruct.2016.02.037