Issue 49

L. Suchý et alii, Frattura ed Integrità Strutturale, 49 (2019) 429-434; DOI: 10.3221/IGF-ESIS.49.41 432 Parameter Symbol Value Hub diameter D iH 45 mm Hub outer diameter D oH 95 mm Joining length Lj 5 mm Hub chamfer angle φ 15°, 90° Geometric interference I geo 0.4 mm Shaft diameter D oS 45.4 mm Table 1: Geometry parameters of investigated inner knurled interference fit connection Yield stress, MPa Tensile strength, MPa Strain to rapture, % Hardness 16MnCr5 426 (untreated) 632 (untreated) 26.9 (untreated) 785 HV (case hardened) C45 387 (untreated) 664 (untreated) 25.7 (untreated) 233 HV (untreated) Table 2: Material properties. Results In comparison to the presented references, the maximum joining force (Figure 3a) of connections joined by cutting ( φ = 90°) is also lower than the one of the formed connection ( φ = 15°). In contrast to the cutting method, where material is separated through chip formation, forming methods generate a higher friction force due to higher deflected radial forces. Characteristic curve features of the joining forces can be extracted as well as described in [14]. Compared to forming joining, for cutting I-KIF a higher slope can be determined at the beginning of the joining process (Figure 3a). The bend at approx. 1 mm of the stroke represents the pure cutting force. The following increase of the force can be linked to the increasing friction force due to the passive cutting force and growing contact area. (a) (b) Figure 3 : a) Joining forces of cutting and forming I-KIFs, b) Fatigue test results related to smooth surface of Ø45 According to the Coulomb friction and the pressure-force-area-expression, the frictional force will grow with stroke. The last section of the joining curve ( φ = 90°) corresponds to the pure friction force at fully shaped joining length L j. This force level also corresponds to the maximal axially transmittable force of the connection.