Gestaltfestigkeit von Pressverbindungen

FKM 2009
Issue number 305
Project no. 276

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Final report
Abstract:

As part of the research project, the design strength and notch coefficient for selected press connection geometries and materials were determined. In addition to supplementing the existing characteristic values, the focus of the investigations was also on the statistical validation of the notch effect numbers contained in the relevant standards. To this end, several Wöhler curves were determined.
The evaluation of these results shows that the notch effect coefficients currently contained in the standards for interference fits (PV) with a smooth shaft can be retained for both bending and torsion. Case-hardened PV exhibit a significantly higher strength of shape compared to the quenched and tempered steel C45E, which is why the surface hardening factor KV must be adjusted accordingly. With the shaft diameters that can be realized on the existing test benches (25 to 60 mm), a size influence could not be proven with certainty. It is therefore recommended that the size influence factor K3 contained in DIN 743 should continue to be used for PV. The comparative studies on the influence of material showed qualitatively the well-known fact that the fatigue strength of higher-strength materials increases, but at a much lower rate than the tensile strength. The notch effect figures therefore differ significantly.
It can be deduced from some literature that slippage leads to a noticeable reduction in strength. This behavior should be verified by reducing the joint pressure [from pF (QA = 0.5) = 133 N/mm2 to pF (QA = 0.75) = 78 N/mm2]. The tests led to the surprising result that a lower joint pressure in no way significantly worsens the fatigue strength. Admittedly, this statement only applies here to the joint pressure reduced to 20