umat_finite_viscoelasticity

This repository consists the work of my Mini Thesis titled "Implementation of a Viscoelastic Model for Hydrogels in ABAQUS" for the M.Sc. Computer-Aided Mechanical Engineering course at RWTH Aachen University. The outcome of this work was a User Material Subroutine based on the Finite Viscoelasticity Theory with multiple relaxation mechanisms and 1-parameter Ogden Models for the strain energy function.

Contents:

• UMAT : ABAQUS User Subroutine FORTRAN Files (UMAT)
• optimization : MATLAB Live Scripts and Functions for parameter optimization using Levenberg-Marquardt optimization
• report : LaTeX source and figures used for generating reportAJC.pdf

Changelog:

• 09.02.24 : Update feedback from XF Cheng
  • 1. Fix incorrect coefficient in UMAT files (residual calculation, c.f. Eq. 2.154 & 2.155 -> 1/(3*4) instead of 1/6)
  • 2. Fix incorrect sign in Report Eq. 2.158 and correspondingly update UMAT files
• 02.05.24 : Update feedback from Shields602
  • 1. Delete unused computation of BTOTV, and SPRIND call in UMAT files.