The fatigue life gage



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This thesis describes the present state of development of the fatigue life gage which generates an irreversible resistance change which is a continuous function of the fatigue experience of the structure to which it is attached. Values of 7.52 per cent resistance change for 2024 T4 aluminum and 5.07 per cent resistance change for CRS 1018 at crack initiation are obtained using NA-01 fatigue gages. Results of the tests are quite consistent. The instant at which the first fatigue crack occurs is a vital point in the life of a structure, and sometimes the useful life ends very shortly thereafter. The fatigue gage, which permits prediction and prevention of that initial crack, thus becomes an extremely important device. In time, it may become a more important device than the electric resistance strain gage. As is true with any precision measuring device, the successful use of the fatigue gage depends upon intelligent application, meticulous care in installation, and in measurement of gage output and proper interpretation of response.