Figure 3.

(a) The fiber network is embedded within the volumetric element mesh, and they interact with the solid element through virtual nodes (solid and filled circles). The fibers can interact with the elements in three ways: 1) pass completely through the element, 2) partially pass through the element, or 3) lie entirely within the element. Solid circles are the endpoints of the fibers that lie on the boundary of the volumetric element while open circles lie within the volumetric element. The fibers are represented in the finite element formulation by their endpoints stored as virtual nodes defined by their isoparametric coordinates with respect to the element. For fiber nodes within the element, the endpoints are found directly. Endpoints on the boundary of the element are found through a line-plane intersection of the element face and the fiber. (b) The fiber material model is bilinear, with the fiber force zero until the recruitment stretch, λ_r, is reached. Slope of the linear curve beyond the recruitment stretch is the elastic modulus (E_f) for the fiber.