Notch stress formulae are derived for the application of a notch stress approach to the fatigue assessment of spot welds. A keyhole notch is assumed to describe the edge of the weld spot between the overlapping plates. The stress fields at the keyhole notch under ‘singular’ and ‘non‐singular’ in‐plane loading modes inclusive of the stress concentration factors Kt are derived from the relevant Airy stress functions. The formulae are applied to typical loading cases of spot welds and compared with finite element solutions. Fatigue‐effective notch stresses inclusive of fatigue notch factors Kf are calculated by applying the microstructural support hypothesis of Neuber. The notch stresses at the keyhole are also derived for out‐of‐plane shear loading based on the relevant harmonic stress functions. The multiaxial notch stresses at the weld spot edge are thus completely described.
Autofrettage is a local surface strengthening procedure to enhance the fatigue resistance of pressurized components. It is used since the beginning of the 20th century. The beneficial effect of the autofrettage is based on compressive residual stresses, which are induced by a single pressure overload applied before the service loading. This pressure overload is much higher than the subsequent service pressure.In the present contribution, a survey over the state of the art of the development of calculation concepts is given. After the presentation of some experimental results, which are the starting point for different calculation concepts, these concepts will be explained and used. In the end an outlook on finite life design and variable amplitude loading is given.
KurzfassungZur Bewertung der Ermüdungsfestigkeit nahtgeschweißter Feinblechverbindungen stehen verschiedene Konzepte zur Verfügung, die sich grundsätzlich in der Art der erforderlichen Eingabegrößen voneinander unterscheiden. Im Rahmen der dargestellten Untersuchungen werden verschiedene Berechnungskonzepte vor dem Hintergrund der Notwendigkeit einer verbesserten rechnerischen Lebendauerprognose analysiert und exemplarisch auf Probenebene angewandt. Betrachtet werden das Kerbspannungskonzept mit und ohne Stützwirkungsansatz und das Kerbdehnungskonzept. Die erforderlichen Eingabegrößen werden durch numerische und experimentelle Untersuchungen ermittelt. Die berechneten Lebensdauern werden aktuellen experimentellen Ergebnissen gegenübergestellt. Auf der Basis der Erkenntnisse der oben angegebenen Grundlagenuntersuchungen erfolgt die Erweiterung des kommerziellen Lebensdauerberechnungsprogramms Femsite, das in der Serienberechnung eingesetzt wird.
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