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Modelling the influence of porosity on fatigue strength of sintered steels
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
2019 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The pores in pressed and sintered components constitute weak points in the material since the stress concentration is larger than the nominal stress there. Therefore, fatigue cracks initiate at the pores. Specifically, it can be assumed that the fatigue cracks initiate at the largest pore in the stressed volume. Studies have previously looked at finding ways to model the fatigue strength of the material based on the largest pore.

This thesis looks at a model previously derived for hardened pressed and sintered materials that is based on linear elastic fracture mechanics and investigates if said model can be modified to include non-hardened pressed and sintered materials that do not necessarily behave linear elastically. A model describing the influence of the size of the largest pore on the fatigue limit using empirical coefficients is suggested. Furthermore, the area of the largest pore is modelled using extreme value statistics.

The model proved successful in modelling the density effect of the porosity on the fatigue strength for two materials with different microstructures: one with a homogeneous microstructure and one with a heterogeneous microstructure. For the material with the homogenoeous microstructure the model also accounted well for the notch effect when tested on samples with a different geometry. However, for the heterogeneous material the model did not account for the notch effect. Deformation hardening due to local plastic deformation in the softer phases was suggested as a possible explanation and was supported by tensile tests.

Place, publisher, year, edition, pages
2019.
Series
UPTEC K, ISSN 1650-8297 ; 19031
Keywords [en]
Fatigue, Powder metallurgy, PM, sintered steels, fracture mechanics, porosity, metal powders, fatigue strength, fatigue limit
Keywords [sv]
utmattning, pulvermetallurgi, metallpulver, utmattningsgräns, brottmekanik, porositet, sintring
National Category
Chemical Engineering Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:uu:diva-398977OAI: oai:DiVA.org:uu-398977DiVA, id: diva2:1377336
External cooperation
Höganäs AB
Educational program
Master Programme in Chemical Engineering
Supervisors
Examiners
Available from: 2019-12-20 Created: 2019-12-11 Last updated: 2019-12-20Bibliographically approved

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  • apa
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