ABSTRACT
The strain method of fatigue analysis predicts the life expectancy of a machine part based on the magnitude of fluctuating strain. The following is a two-part theory presentation of the strain method: basic one-dimensional theory applicable to simple bodies subject to axial loading and multiaxial theory considering the true geometry and true loading. The empirical information that leads to the theory of the strain method is obtained from low cycle fatigue tests where a metal specimen is subjected to cyclic loading. The computer reads the load and strain signals from the sensors and responds with command signals to the controller. The tests with stress control have the prescribed stress fluctuation data stored in computer memory, while the tests with strain control have the strain data stored. In real life, the metals do respond to the cyclic loading with changes of either strain hardening or strain softening.
