Fig shows Fr evaluated during the
Fig. 5 shows Fr evaluated during the first penetration, Fr measured during the second penetration (or the Coulomb friction force), and finally, the wood deformation–fracture force obtained after subtraction of the friction force from the first force distribution. In addition to the raw data, the graphs include fitted model evaluations. For both nail geometries, the curves indicate that the tip penetration Hexa His Π2?0.09 is dominated by the deformation–fracture force. While this force component remains practically constant at 200 N after Π2Π2 = 0.1 for the smooth nail, the cross-section increase above the nail tip of the annularly threaded nail extends the deformation influence development up to roughly Π2Π2 = 0.4, and leads to a maximum value close to 400 N, which remains nearly constant thereafter. On the other hand, the friction forces show a linear influence for both nail shanks. However, since this component results mainly from adhesion at the wood–nail interface, the real contact area reduction resulting from the annular surface of the second shank type decreases the friction contribution compared to the smooth shank. The maximum friction reaches 708 N at Π2Π2 = 1 for the smooth nail, which corresponds to 81% of Fr, while for the annular shank the friction maximum value is 419 N or 55% of Fr. Finally, based on these observations, and comparing the three nail geometries, it could be conjectured that the penetration resistance force generated by a helically threaded nail should be dominated by an adhesive friction force component.