(c)
Fig. 2. Cyclic hardening/softening curves and mean stress in OPD TMF
cycling for four strain amplitudes; (a) stress amplitude vs. the number
of cycles, (b) plastic strain amplitude vs. number of cycles, (c) mean
stress vs. the number of cycles.
Cyclic stress-strain curve from OPD-TMF tests is plotted in Fig. 3. For
comparison also the cyclic stress-strain curves from IP-TMF, OP-TMF and
IPD-TMF tests are shown here. Stress amplitude σais plotted vs. plastic strain amplitude εap , both
at half-life. Cyclic stress-strain curves for OP-TMF and OPD-TMF cycling
lies well above those for IP-TMF and IPD-TMF cycling and have higher
slopes. The introduction of the dwell time at maximum temperature
results in the shift of the cyclic stress-strain curves to lower stress
amplitudes, both in IP and in OP cycling. This shift is more pronounced
in OPD-TMF cycling.