Fatigue Life Chart_1
description
Transcript of Fatigue Life Chart_1
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Glenn Research Center at Lewis Field
Random Vibration Testing of Hardware Tutorial
3
Notes taken from Dynamic Environmental Criteria
NASA-HDBK-7005, March 13, 2001
N = c S b
T F = c
b
x
Inverse Power Law Model (time-to-
failure related to rms dynamic loading) Equivalency Equation for two
rms dynamic loads and times
Idealized S-N Curve for Structural Materials
Special case of the inverse power
law describing the S-N curve
(ignoring the fatigue limit)
N = number of loading cycles to failure
S = peak stress
b and c are material constants
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Glenn Research Center at Lewis Field
Random Vibration Testing of Hardware Tutorial
4
Fatigue Life Assessment Requires
Prototype Hardware Program
Prototype programs allows an assessment to be
made of remaining fatigue life:
Qualification testing of the qualification hardware establishes
the test demonstrated fatigue life for the hardware design.
The identically-designed flight hardware may confidently be
acceptance tested and launched, if these events do not
extend beyond the previously demonstrated fatigue life.
Any remaining fatigue life can be allotted to additional ground
tests, reflights, etc.
Protoflight programs have no test demonstrated
fatigue life.
Unknown remaining fatigue life.