Discontinuous fiber reinforced polymers are one of the most used materials in mass production, showing a complex behavior, composing a transient chemo-thermomechanical matrix and fiber-induced anisotropic physical properties. The fiber-induced anisotropic behavior occurs not only in structural properties, but also during material flow, which in turn influences the final physical properties by a different mold filling. Therefore, the fibers influence the material flow and vice versa, the material flow causes fiber-reorientation. To account for the fiber-flow interactions, the proposed simulation method for injection molding describes the fiber-induced anisotropic flow behavior by a fourth order viscosity tensor. Furthermore, fiber breakage is taken into account and the calculated fiber length directly influences the modelling of fiber orientation and flow progression. Numerical examples demonstrate the fiber length dependent effects to verify the model implementations.