Bei Brückenlaufkranen werden die Radlasten in die unterstützenden Kranbahnträger über deren Obergurte eingeleitet. Die Konstruktionsdetails im Obergurtbereich, d. h. die Anschlüsse und Verbindungen, erfahren dabei einen mehrachsigen Spannungszustand infolge der Radlasteinleitung und der gleichzeitigen Biegung des Kranbahnträgers. Zu diesen Konstruktionsdetails zählt bei geschweißten Kranbahnträgern die Flansch‐Steg‐Verbindung, die Gegenstand dieses Beitrags ist. Die wiederholte Überrollung von Kranbahnträgern durch Radlasten führt aufgrund der konzentrierten Lasteinleitung und der geometrischen Kerbwirkung der Konstruktionsdetails zu einer mehrachsigen Ermüdungsbeanspruchung. Da diese mehrachsige Ermüdungsbeanspruchung durch eine Phasenverschiebung der Spannungskomponenten gekennzeichnet ist, wird sie als nichtproportional bezeichnet. Die für den Ermüdungsnachweis erforderlichen Ermüdungsfestigkeiten im Eurocode 3 – aber auch in den ehemaligen nationalen Normen – beruhen bislang auf Analogiebetrachtungen zum Doppel‐T‐Stoß, dem Kreuzstoß, unter Zugbeanspruchung und stützen sich nicht auf Versuchsergebnisse am eigentlichen Konstruktionsdetail ab. Im IGF‐Forschungsvorhaben FOSTA P895 wurde die Ermüdungsfestigkeit von Kranbahnträgern mit nicht durchgeschweißter Flansch‐Steg‐Verbindung durch eine Kombination aus Ermüdungsversuchen mit überrollender und ortsfest schwellender Radlast ermittelt. Ziel der Untersuchungen war es, die nichtproportional mehrachsige Ermüdungsbeanspruchung der Flansch‐Steg‐Verbindung zuverlässiger bewerten zu können.Test‐based fatigue strength of constructional details with wheel load application – Investigations on partial penetration flange‐to‐web connections. In case of bridge cranes, the wheel loads are applied to the supporting crane runway girders through their top chords. The constructional details of the top‐chord region, i. e. the joints and connections, are subjected to a multiaxial stress state due to the wheel load introduction and the global bending of the crane runway girder. For welded crane runway girders, the flange‐to‐web connection is one of these constructional details and subject of this article. The frequent travelling of wheel loads over a crane runway girder leads to a multiaxial fatigue stress due to the concentrated load introduction and the notch effect of the constructional details. As the multiaxial fatigue stressing exhibits a phase shift between the stress components, it is referred to as nonproportional. The fatigue strengths of Eurocode 3 being necessary for the fatigue evaluation were derived in analogy with the tension‐loaded cruciform joint and are not test‐based for the considered constructional detail. In the IGF research project FOSTA P895, the fatigue strength of partially penetrated flange‐to‐web connections were determined through a combination of fatigue tests on crane runway girders with travelling and stationarily pulsating wheel load. The project aimed at a more reliable evaluation of the nonproportional multiaxial fatigue stress of the flange‐to‐web connection.
This publication is focused on a critical plane approach to assess the influence of the multiaxial stress state on the lifetime of welded crane runway girders cyclically stressed by travelling wheel loads. Cyclic stress-strain curves of specimens both from the weld region and the base material of the girder are evaluated in strain-controlled reversible fatigue tests as a basis for the assessment of the lifetime. Finite element analyses are performed to estimate the multiaxial and non-proportional local stress condition acting on sharp notches of the girder, i. e. the weld toes and the weld root. The MPA AIM-life concept is used to evaluate the lifetime of crane runways on the basis of advanced fatigue parameters and the cyclic material properties. Furthermore, the notch stress approach according to IIW guideline [1] is applied to investigate the fatigue behavior. The estimated lifetimes are compared to experimental results of component fatigue tests conducted with full-scale welded crane runway girders.
During the past decade the demand for high performance automotive electronics is steadily increasing. An efficient development of such products requires the use of durability assessment techniques throughout the whole design optimization process. Since typical components comprise a large number of different materials and complex geometrical structures, Finite Element (FE) analysis is preferably used for durability evaluation and continuously replaces analytical calculations. However, a direct lifetime calculation by means of FE-techniques is still not achieved, partly due to the lack of material models capable of mapping the intrinsic material degradation under the relevant thermo-mechanical loads. Here, we propose a material model for a tin-based solder alloy which describes the non-linear mechanical behavior at the beginning of deformation as well as during continuous cyclic aging. We investigated the evolution of the mechanical properties and microstructure of the solder alloy Sn96:5Ag3:5 by cyclic strain-rate controlled fatigue- and creep-tests on as-casted standardized specimens. Material modeling is focused on the description of the complex interplay between viscoplastic, fatigue and creep processes observed in the experiment. Finally, a very good agreement is obtained between the measurements and the numerical model, which can offer new opportunities for lifetime simulations of lead-free solder joints
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