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

In FEBio a prestrain can be defined for most materials that allows the user to prestrain or prestress the model before loading is applied. This is useful for modeling biologically tissues that exhibit residual strain, or whose initial state cannot assumed to be stress-free (e.g. arteries from in-vivo image data.)