Damage Tolerant Design Concepts for the Application of High strength Materials in Railway Switch Components

Stefan Kolitsch

Research output: ThesisDoctoral Thesis

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Abstract

Switch components, especially switch blades, are highly loaded rails. The high loads are a result of small bending radii during the manufacturing process and high dynamic forces due to the wheel contact transition from the stock to the switch rail. Dealing with those high loads, it requires an improvement of the wear resistance and the application of high strength materials. The implementation of new material types demands applications of new design concepts and the comparison to the manufacturing processes of conventional materials. For this reason, in the present thesis, modified and new damage tolerant design concepts, for the static failure during the bending process and the dynamic behavior in track, have been investigated. Furthermore, the application of four different material types with different tensile strengths and microstructures have been analyzed. For the development of a design criterion in the bending process, specimens with different crack lengths have been tested until failure. In consideration of the load and small flaws, a new concept, the somewhat modified static strain based Kitagawa-Takahashi diagram, is investigated. Here, the nominal failure strain in the outer fiber, due to the bending load, is plotted over the flaw size. The failure strain is estimated by fracture mechanics criteria, using the J-integral as a crack driving force and compared with the experimental results for the different material types. For cyclically loaded components, two different approaches are compared. The Smith diagram for different loads and surface conditions is presented in the stress based approach. Additionally, the estimated failure curves are compared with fatigue experiments at selected load ratios and surface conditions. Considering cracks, the Kitagawa-Takahashi diagram represents the endurable stress range and is represented for the different material types and stress ratios in the fracture mechanics approach. Furthermore, for the analytical calculation of the crack growth, an enhanced method for the calculation of the geometry factor is investigated. This method provides the possibility to calculate the stress intensity of semi-elliptical cracks, where the crack is close to the specimen boundaries for tension and bending around two axes. Moreover, the influence of the stress concentration of a notch on the crack growth behavior of short cracks is investigated by experiments. For this purpose, an advanced method with respect to the direct current potential drop method is used for estimation of crack lengths, considering semi-elliptical shapes. The experimental results are then compared with the analytically calculated solutions of the crack growth behavior, considering plastic deformation in front of the notch root.
Translated title of the contributionSchadenstolerante Auslegungskonzepte für den Einsatz hochfester Materialien in Weichenbauteilen
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Pippan, Reinhard, Assessor A (internal)
  • Antretter, Thomas, Assessor B (internal)
Publication statusPublished - 2017

Bibliographical note

embargoed until null

Keywords

  • Damage tolrerant design
  • fracture mechanics
  • rail way switches
  • static failure
  • crack growth

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