Fatigue assessment

Patent metadata

Field	Value
Publication number	US-9222865-B2
Application number	US-201313974565-A
Country	US
Kind code	B2
Filing date	Aug 23, 2013
Priority date	Aug 23, 2013
Publication date	Dec 29, 2015
Grant date	Dec 29, 2015

Abstract

Methods are disclosed relating to the assessment of fatigue damage in objects that include for example, subjecting a fatigued object to a cyclic mechanical stress, measuring a rate of temperature rise in the fatigued object, and assessing a degree of fatigue of the fatigued object based on the rate of temperature rise in the fatigued object. Methods of measuring internal structural characteristics and methods of correlating fatigue damage to results from excitation tests are also taught.

First claim

We claim:

1. A method of evaluating fatigue comprising:
a. subjecting a fatigued object to a cyclic mechanical stress;
b. measuring a rate of temperature rise in the fatigued object; and
c. assessing a degree of fatigue of the fatigued object based on the rate of temperature rise in the fatigued object;
d. wherein the assessing of the degree of fatigue comprises comparing the rate of temperature rise in the fatigued object to information from a different temperature rise test on a different object;
e. wherein the rate of temperature rise is measured at the beginning of the subjecting of the fatigued object to the cyclic mechanical stress;
f. wherein the measuring of the rate of temperature rise in the fatigued object occurs during an excitation test;
g. wherein the fatigued object is an object that has previously undergone substantial micro-structural fatigue changes;
h. wherein the degree of fatigue assessed is representative of an amount of fatigue experienced prior to the excitation test; and
i. wherein the amount of fatigue experienced prior to the excitation test is unknown prior to the excitation test.

2. The method of claim 1 wherein the fatigued object has a substantially uniform temperature prior to the step of subjecting the fatigued object to the cyclic mechanical stress.

3. The method of claim 1 wherein the cyclic mechanical stress is selected from shear stress, tensile stress, and compressive stress.

4. The method of claim 1 wherein the different object has a macroscopic structure similar to the fatigued object.

5. The method of claim 1 wherein the fatigued object is metallic.

6. The method of claim 1 wherein the fatigued object is plastic.

7. The method of claim 1 wherein the fatigued object is a composite material.

8. The method of claim 1 wherein the fatigued object is heterogeneous.

9. The method of claim 1 wherein the fatigued object is a rigid object.

10. The method of claim 1 further comprising:
a. expending a portion of a service life the fatigued object prior to measuring the rate of temperature rise;
b. wherein the cyclic mechanical stress is part of an excitation test.

11. A method of characterizing useful life comprising:
a. conducting a first rate of temperature rise test comprising:
i. allowing an object to come to a substantially uniform rest temperature,
ii. subjecting the object to a cyclic stress sufficient to provide a temperature increase, and
iii. taking a first measurement of a first initial rate of temperature rise;

b. repeatedly applying a primary load stress to the object;
c. tracking the application of the primary load stress;
d. conducting a second rate of temperature rise test after the repeated application of the primary load stress, with the second rate of temperature rise test comprising:
i. allowing the object to come to the substantially uniform rest temperature,
ii. subjecting the object to the cyclic stress, and
iii. taking a second measurement of a second initial rate of temperature rise; and

e. correlating the second measurement with a degree of fatigue;
f. wherein the second measurement of the second initial rate of temperature rise occurs during an excitation test and
g. wherein the object is an object that has undergone substantial micro-structural fatigue changes during the application of the primary load stress to the object.

12. The method of claim 11 further comprising the step of continuing subjecting the object to the primary load stress until the object experiences mechanical failure.

13. A method of evaluating fatigue comprising:
a. subjecting a first object to a first load stress until the first object fails;
b. performing a series of excitation tests on the first object wherein the series of excitation tests is carried out over a life of the first object;
c. preparing a set of initial slope of temperature rise data from the series of excitation tests;
d. subjecting a second object to a second load stress sufficient to fatigue the second object;
e. subjecting the second object to a subsequent excitation test
f. determining a subsequent initial slope of temperature rise in the second object during the subsequent excitation test; and
g. evaluating a degree of fatigue of the second object based on the subsequent initial slope of temperature rise in the second object during the subsequent excitation test and the set of initial slope of temperature rise data from the series of excitation tests;
h. wherein the first object has a first object macroscopic structure;
i. wherein the second object has a second object macroscopic structure; and
j. wherein the first object macroscopic structure is similar to the second object macroscopic structure prior to failure of the first object.

14. The method of claim 13 further comprising the step of indicating a percentage of the service life consumed for the second object.

15. The method of claim 13 further comprising the step of expressing the degree of fatigue as a function of the subsequent initial slope of temperature rise.

Assignees

• Khonsari Michael M
• Amiri Mehdi
• Univ Louisiana State

Inventors

• Khonsari Michael M
• Amiri Mehdi

Classifications

• G01N2203/0694

  Temperature · CPC title

• G01N2203/0222

  Temperature · CPC title

• G01N2203/0073

  Fatigue · CPC title

• G01N2203/0005

  Repeated or cyclic · CPC title

• G01N3/34 Primary

  generated by mechanical means, e.g. hammer blows · CPC title