Fatigue assessment
Methods of evaluating mechanical fatigue using nondestructive techniques are described herein. Such techniques involve mechanically testing a component to establish a relationship between some measure of actuation and a temperature profile produced during the testing. Measurements from a separate external heating test that generates a similar temperature profile on the component may then be used to generate an estimate of a fatigue lifespan of the component by utilizing data from those tests.
1 . An evaluation method comprising:
a. conducting a first cyclic mechanical test of a component thereby establishing a relationship between a measure of actuation during the first cyclic mechanical test and a first temperature profile of the component;
b. conducting a first external heating test comprising externally heating the component generating a second temperature profile matching the first temperature profile; and
c. estimating a fatigue lifespan of the component based on an observed surface temperature and an observed external heating power.
2 . The method of claim 1 wherein the measure of actuation is a measure of stress.
3 . The method of claim 1 wherein the measure of actuation is a measure of strain.
4 . The method of claim 1 wherein the measure of actuation is a measure of displacement.
5 . The method of claim 1 wherein the component is subjected to compression during the first cyclic mechanical test.
6 . The method of claim 1 wherein the component is subjected to bending during the first cyclic mechanical test.
7 . The method of claim 1 wherein the component is subjected to tension during the first cyclic mechanical test.
8 . The method of claim 1 wherein the component is subjected to shear loading during the first cyclic mechanical test.
9 . The method of claim 1 wherein the component is subjected to torsion during the first cyclic mechanical test.
10 . The method of claim 1 wherein the first cyclic mechanical test exposes the component to a level of fatigue exceeding an endurance limit of the component.
11 . The method of claim 1 further comprising evaluating an energy dissipation rate based on a cooling test on the component.
12 . The method of claim 1 further comprising evaluating an initial slope of temperature rise at an onset of mechanical fatigue of the component.
13 . The method of claim 1 wherein a first portion of the observed external heating power corresponds to a damaging portion of power applied in the first cyclic mechanical test.
14 . The method of claim 1 further comprising a second cyclic mechanical test on the component conducted at a different fatigue amplitude.
15 . The method of claim 1 wherein the observed surface temperature is a steady-state temperature.
16 . An evaluation method comprising:
a. conducting a first cyclic mechanical test of a component thereby establishing a relationship between a measure of actuation during the first cyclic mechanical test and a first temperature profile of the component;
b. conducting a first external heating test comprising externally heating the component generating a second temperature profile matching the first temperature profile; and
c. estimating a fatigue lifespan of the component based on an observed surface temperature and an observed external heating power according to the equation:
N
f
=
FFE
fT
s
β
(
P
-
P
*
)
;
d. wherein FFE is fracture fatigue entropy;
e. wherein f is frequency;
f. wherein T s is absolute surface temperature:
g. wherein β is an experimentally determined parameter;
h. wherein P is power consumed;
i wherein P* is a non-damaging portion of the power consumed; and
j. wherein N f is a number of cycles to failure.
17 . The method of claim 16 further comprising evaluating an energy dissipation rate based on a cooling test on the component.
18 . The method of claim 16 further comprising evaluating an initial slope of temperature rise at an onset of mechanical fatigue of the component.
19 . The method of claim 16 wherein the measure of actuation is a measure of displacement.