Hysteresis Loop-Constant Amplitude Loads

A specimen of ductile cast iron (DCI) carrying a notch is subjected to a load cycling under strai controlled condition. On the notch root the strain excursion is equal to 20,000 ps, as shown in Fig. 6.30a. The cyclic stress-strain characteristic of the material has been experimentally found to be 

6 Strain-Based Fatigue Analysis Low Cycle Fatigue 

It s Young s modulus is = 170,000 MPa. Determine the hysteresis loop of the material. For the initial loading ramp Eq. (6.3) will be used 

The entire loading curve can be found giving the strain s growing values dividing the interval 0 0.01, for instance, in 5 steps of 0.002 each. Table 6.2 lists the results. 

Therefore the hnal point A of the loading ramp has coordinates = 0.01 and = 403 MPa, Fig. 6.30b. The next step is to build the unloading ramp. To this purpose Eq. (6.6) will be used with the starting point A = (0.01 403). The quation will be solved by iteration with a step-by-step procedure using, as before, a strain unloading step As = 0.002. For the hrst step it is 

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