Inner knurled interference fits (IKIFs) enable backlash-free and space-optimised load transfer, particularly in thin-walled hubs. Their static load-bearing capacity is governed by the plastically deformed contact zones formed when an oversized shaft is joined into an inner knurled hub. Existing calculation approaches, primarily developed for outer knurled interference fits (OKIFs), neglect local inhomogeneities and fail to capture the coupled interaction of form-fit and friction-based load transfer. This leads to systematic deviations in the prediction of joining and static torsional load capacities. This paper presents an analytical calculation method for IKIFs that explicitly couples form-fit and frictional load-transfer effects across the profile height and along the joint length. The method is based on experimental and numerical analyses of the contact zone during forming and static torsional loading. Validation against tests results on IKIFs with uniform joint diameter demonstrates strong agreement in joining force and static load-bearing capacity, enabling reliable and conservative design, even for thin-walled components.
Hentschel et al. (Mon,) studied this question.