After 150 Years Of Research, Fatigue Still Causes
85% Of Failures
Author(s)
J. Volak & V. Mentl
Abstract
The fatigue phenomenon is said to be responsible for more than 80% of
structural failures and operational accidents. One of the most important branches
of industry, where unexpected outages can cause extremely expensive costs is
the power producing industry. The steam turbine rotors represent large,
expensive and, in the case of failure, potentially dangerous components. Their
local properties generally differ from one forging to another, or if we compare
head and bottom parts of the original ingot, or central and circumferential
locations of one rotor body respectively, or if we compare the properties of
separate discs, e.g. in the case of welded rotors. These differences stem from
both even slight changes in the chemical composition (of separate heats or even
within one ingot), heat treatment and in the differences in technology with
respect to the real shape and size of the forgings in question.
At present, questions on quantitative evaluation of remaining lifetime (to
avoid failure) become urgent and, because fatigue is the most frequent cause of
material degradation and resulting structural components failures, the remaining
lifetime assessment is based on the evaluation of mechanical properties before
and after some time of service. The original material data are usually tested by
means of classic test specimens, which can hardly be used in the case of
components in service, where there is no possibility to withdraw a sufficient
volume of representative material for the manufacturing of a classic test
specimen. In such cases today, methods of semi-destructive removal of a small
volume of test material are utilized. This makes it possible to produce miniature
test specimens.
This paper describes the results of fatigue tests performed on miniature test
specimens in comparison with the classic fatigue tests for several alloys applied
Keywords
fatigue, failure risk assessment, remaining lifetime evaluation
Related Book
Other papers in this volume
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