"User-Programmable Features (UPFs) are an extremely useful feature for analysts that need
additional advanced functionality, especially in the area of constitutive modeling.
TB,HYPER allows users to include many incompressible and compressible hyperelastic
material behavior – Ogden, Arruda-Boyce, Gent, Yeoh, Blatz-Ko are but some of the
available models. However, for those wishing to use a customized strain energy function,
the USERHYPER.F subroutine is available."
(Week 39, week of 09/30/07.)