Fatigue Life Prediction
Using the Strain-Life Approach
A case study examining a stepped shaft used for a bearing test fixture
Frank M. Kelso
Objectives
The traditional approach to fatigue life prediction is based on
the stress levels in the component, and the S-N diagram for the component
material. An alternative approach to life prediction relies on the correlation
between strain and life rather than stress and life.The purpose of this case
study is to practice using the strain-life approach to fatigue life prediction,
and compare its results to the traditional approach (for this particular
component.)
An additional goal is to gain some familiarity with stainless steel
in fatigue, so we will assume that the shaft is made out of 316L rather
than the actual plain carbon steel currently in use.
Details of the Case Study
A shaft used in a bearing test fixture is experiencing fatigue failure
at the fillet.The shaft is made of 316L stainless steel, and the bending
moment is 40.2 in-lb (4.54 N-m) at the critical location.The fillet has been
ground and polished in an attempt to increase its fatigue life.
Connecting Shaft, Bearing Test Fixture
Dimensions are shown in the figure below.
Shaft Dimensions
Fatigue properties for the stainless steel are provided on the
316L datasheet.
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design questions.
© 1998 Frank M. Kelso. All Rights Reserved. Last modified:
Friday, February 20th, 1998 /fmk/ |
