$\newcommand{\Dev}{\operatorname{Dev}}$ $\newcommand{\dev}{\operatorname{dev}}$ $\newcommand{\grad}{\operatorname{grad}}$ $\newcommand{\divg}{\operatorname{div}}$ $\newcommand{\Ei}{\operatorname{Ei}}$ $\newcommand{\tr}{\operatorname{tr}}$

Unlike the materials in Section 4.1.2↑, these materials do not necessarily assume an additive decomposition of the bulk and deviatoric parts of the strain energy or stress. Further, these materials can only be used with the standard displacement-based finite element formulation, rather than the three-field element formulatoin. They should not be used for nearly-incompressible material behavior due to the potential for element locking.