Method for Measuring Fatigue

• US 20130305833A1
• Filed: 05/17/2012
• Published: 11/21/2013
• Est. Priority Date: 05/17/2012
• Status: Active Grant

• Current Assignee: DEPARTMENT OF THE NAVY - NAWCAD
• Original Assignee: Department of Navy Office of Councel - Nawcad
• Inventors: Kittur, Madan
• Granted Patent: US 8,707,795 B2
• Time in Patent Office: Days
• US Class Current: 73/774
• CPC Class Codes: G01M 5/0033 by determining damage, crack or wear
• CPC Class Codes: G01M 5/0083 by measuring variation of impedance, e.g. resistance, capacitance, induction
• CPC Class Codes: G01N 3/32 by applying repeated or pulsating forces

Abstract

A method for measuring fatigue on a metal or metal alloy structural part, which includes mounting a fatigue gage on a surface of the part, the fatigue gage being the same material as the part, applying electrical power on the gage and measuring the resistance of the fatigue gage, inspecting the fatigue gage at various time intervals by applying electric power on the gage and measuring the resistance of the fatigue gage; and analyzing the change of resistance of the fatigue gage at the various time intervals to determine fatigue on the part.

Claims

1. A method for measuring fatigue on a metal or metal alloy structural part, comprising:

(a.) mounting a fatigue gage on a surface of the part, the fatigue gage being the same material as the part;

(b.) applying electrical power on the gage and measuring the resistance of the fatigue gage;

(c.) inspecting the fatigue gage at various time intervals by applying electric power on the gage and measuring the resistance of the fatigue gage; and

(d.) analyzing the change of resistance of the fatigue gage at the various time intervals to determine fatigue on the part.

2. The method of claim 1, wherein the fatigue gage is dog bone shaped.

3. The method of claim 1, wherein the fatigue gage is calibrated prior to mounting.

4. The method of claim 3, wherein the fatigue gages are equipped with a Radio Frequency Identification transponder circuit which can be interrogated for resistance values.

5. The method of claim 4, wherein the fatigue gages are equipped with a wireless transmitter that provides resistance values to a remote receiver.

6. The method of claim 4, wherein the fatigue gages are calibrated by:

mounting a test fatigue gage on a fatigue test specimen with a known stress concentration factor;

subjecting the fatigue test specimen to constant amplitude stress cycles with a known minimum stress/maximum stress ratio, continuing until a crack forms;

applying an electric current to the test fatigue gage;

monitoring and recording the change in resistance the test fatigue gage; and

,

plotting a crack growth curve and a response curve to determine which type of gage should be utilized.