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A Non-Local Theory for the Assessment of Multiaxial High Cycle Fatigue Failure FREE

[+] Author Affiliations
Björn Sjödin

ABB STAL AB, TRS, Finspong, Sweden

Paper No. 98-GT-509, pp. V005T12A012; 8 pages
doi:10.1115/98-GT-509
From:
  • ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition
  • Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education
  • Stockholm, Sweden, June 2–5, 1998
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-7866-8
  • Copyright © 1998 by ASME

abstract

Looking at HCF, the most critical component on the turbine is the blade.

At the present moment there is a need for a HCF criterion suitable for evaluation of stresses calculated with the Finite Element Method. Today there are some, such criterions e.g. Sines. However the criterion does not include important aspects such as the influence of; ‘geometrical size’, ‘stressed volume’ or ‘stress gradient’.

A better understanding of the HCF phenomena would give an increase in the design precision and an opportunity to increase the load on the blades.

A proposal is made for a new theory for HCF assessment. The input required by the theory is roughly the Haigh-diagram for a smooth test specimen.

The theory is a merger between the Sines criterion and the statistical approach made by Weibull. 3 basic assumptions are made; equivalent stresses are calculated according to Sines, ‘the weakest link assumption’ and finally that the fatigue limit for a smooth specimen has a statistical distribution.

Comparing the proposal to classical HCF assessment with Haigh-diagram, the following factors are incorporated:

1, stress concentration factor

2, fatigue notch factor (or notch sensitivity factor)

3, geometric volume dependence

4, different Haigh-diagrams for push-pull, bending and torsion

If the factors are incorporated partially or fully remains to be shown. It is also possible to give a geometrical quantification of the so called ‘stressed volume’.

Qualitative and quantitative tests have been made. Looking at them, the theory looks promising. However, it has to be tested further to get acquainted with any shortcomings of the theory.

Copyright © 1998 by ASME
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