Abstract
Cyclic stress-strain curves were obtained by the incremental step method for a carbon steel SB 49 and a chromium-molybdenum steel SCMV 4. The temperature and strain rate dependences of the cyclic stress-strain curves were discussed and the curves were compared with those obtained by the companion specimens method. The conclusions obtained were as follows:
(1) Cyclic hardening and cyclic softening behaviors were observed for SB 49 and SCMV 4, respectively. The cyclic stress-strain curve lay at the higher stress level side than the monotonic stress-strain curve for SB49; for SCMV 4 it was the other way.
(2) The cyclic stress-strain curve depended on strain rate. With decreasing strain rate, the stress amplitude for SB49 increased at 200 and 300°C, but decreased at 400 and 500°C. Similar dependences were observed in SCMV 4 steel.
(3) The cyclic stress-strain curve can be expressed very well by the experimental equation as Δεt/2=(Δσ/2)/E'+{(Δσ/2)/K'}1/n'
(4) For both materials, the cyclic stress-strain curve obtained by the incremental step method coincided with that obtained by the companion specimens method.
(5) The cumulative damage against the number of blocks to failure in the incremental step tests ranged from 2 to 1/2 for both materials.
