FEBio supports two analysis types, namely quasi-static and dynamic. In a quasi-static analysis, the (quasi-) static response of the system is sought and the effects of inertia are ignored. In the presence of biphasic materials, a coupled solid-fluid problem is solved. In a dynamic analysis, the inertial effects are included in the governing equations to calculate the time dependent response of the system.
Many nonlinear constitutive models are available, allowing the user to model the often complicated biological tissue behavior. Several isotropic constitutive models are supported such as Neo-Hookean, Mooney-Rivlin, Ogden, Arruda-Boyce and Veronda-Westmann. In addition to the isotropic models there are several transversely isotropic constitutive models available. These models are useful for representing biological tissues such as tendons, muscles and other tissues that contain fibers. FEBio also contains a rigid body constitutive model, which can be used to represent materials or structures whose deformation is negligible compared to that of other materials in the overall model. Several constitutive models are available for representing the solid phase of biphasic materials, which are materials that contain both a solid phase and a fluid phase.
FEBio supports a wide range of boundary conditions to model interactions between materials that are relevant to problems in biomechanics. These include prescribed displacements, nodal forces and pressure forces. FEBio provides the ability to represent frictionless and frictional contact. As of version 1.2 it is also possible to model the fluid flow across two contacting poroelastic materials. Finally, the user may specify a body force to model the effects of, for instance, gravity or base acceleration.
FEBio is a nonlinear implicit FE solver and does not have mesh generation capabilities. Therefore the input files, which are described in detail in this document, need to be generated by preprocessing software. The preferred preprocessor for FEBio is called PreView. All MRL software is available free of charge from the MRL Lab website (http://mrl.sci.utah.edu).