The method described in the present work was assessed through the production of composite materials made of polypropylene reinforced with chemical thermomechanical pulp of hemp core fibers. Composite materials were obtained by extrusion and injection molding, and by the addition of a coupling agent to ensure a good interphase between fiber and matrix. In all cases, the composite materials were considered as semi-aligned reinforced. Tensile strength was selected as a representative parameter and was studied by the Kelly-Tyson model.1 Since the original Kelly-Tyson equation was formulated for fully aligned reinforced composite materials, the present work uses a modified one, where the orientation factor is included. The fiber length and diameter distribution were determined by the extraction of the fibers from the composite materials and analyzed in a MorFi equipment. The orientation factor was calculated taking into account the predicted tensile strength for fully aligned composites and the experimental value from the semi-aligned ones. The interfacial shear strength was estimated through Tresca and Von Mises criteria. The values obtained through the simulation were compared to the experimental ones, showing a good correlation between the mathematical model and the experimental part