Münch, Mathias
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Publication Access status: Open Access , On the low temperature creep controlling mechanism in a high strength spring steelDespite of the well-known fact that high strength steels are exhibiting low temperature creep deformation, its rate controlling mechanism is yet to be understood. The strain hardening theory and the exhaustion creep model were proposed almost seven decades ago to unravel the low temperature creep mechanism in a single phase homogeneous isotropic material. However, their applicability to low temperature creep deformation in a technical material like a modern high strength steel is still a matter of investigation owing to their nature of multi-phase, in-homogeneous, and an-isotropic behavior. The authors have grabbed this chance to experimentally validate the exhaustion creep model based on low temperature creep tests of the SAE 9254 spring steel.Source Type:Article297 173 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Zur Bestimmung des Kriechverhaltens martensitischer Federstähle im Niedrigtemperaturbereich(2024)The global transformation process, which consists of the transition from conventional drives, i.e. internal combustion engine, to battery electric vehicles, is forcing the automotive and automotive supply industries to undergo a significant change. However, the CO2 targets for 2030 cannot be achieved solely by expanding electromobility. This also requires an optimization of existing components. The reduction of CO2 emissions can be attained by reducing friction losses in the valve train. The thermal loads up to 423 K within these valve trains demand a high level of creep or relaxation resistance from the high-strength spring steels. Within the scope of this dissertation, the two existing theories for describing the creep behavior of spring steels in the low-temperature range will be verified and the creep rate-controlling mechanism of dislocation glide will be examined. For this purpose, creep tests with valve spring wires under tensile and torsional loading as well as incremental creep tests, i.e. stress-step or temperature-step tests, will be conducted. Finally, it will be reviewed whether the creep behavior of valve spring wires under biaxial loading can be predicted by the knowledge about the creep behavior of martensitic spring steels under uniaxial loading. This will be done by means of numerical methods, which enables the prediction of the creep behavior of helical compression or valve springs in future.Source Type:Doctoral ThesisSeries:Schriftenreihe des Lehrstuhls für Werkstoffsysteme für den Fahrzeugleichtbau im Institut für WerkstofftechnikVolume number:519 90
