The high-strain high-temperature fatigue behaviour of a cast 0·5 Cr-M 0-V steel for steam turbine casings has been evaluated extensively in tests lasting several years. The results define the influence of strain range, dwell period, fatigue-cycle shape, and test temperature on the cyclic endurance. The effect of these parameters on the peak stress and on the stress-relaxation behaviour is also described. A comprehensive review of the data available for Cr-Mo and Cr-Mo-V casing steels suggests that they all have similar resistance to high-strain high-temperature fatigue cracking. An accurate description of the data, facilitating interpolation and extrapolation, is given by ihe relationship established between dwell period and cyclic endurance. However, comparative evaluation of creep-fatigue damage accumulation models together with metal/ographic examination of test specimens indicates that the life-fraction rule provides the best method of predicting the behaviour of steam turbine components in service.MT/531Strain-controlled tests have, therefore, been used to obtain materials data. Much of the information was obtained from mechanical reverse-bend machines 14 since tests with an endurance of five years or more were required' and it is not practical to operate more sophisticated machines continuously over such long periods. However, axial pushpull tests, not continued to specimen failure, were used to provide the cyclic stress-strain data not obtainable from reverse-bend tests. The specimens, of designs used previously,15 were tested at 773, 798, or 823K, covering the most common inlet temperatures of high-temperature steam turbines. Testing was'in air, at a cyclic frequency of O·02Hz (reverse-bend) or 0·01 Hz (push-pull). Tests in steam have a slightly longer endurance than tests in air but the difference in endurance between tests at 0·01 Hz and 0·02Hz is negligible.l 5 -17 Dwell periods of up to 16h were introduced at either the maximum tensile strain (laboratory and type 1 cycles, Fig. I) or at the middle of the strain range (type 2 cycle, Fig. 1), these cycles representing the range of cycles which may occur in a component in service. 6 However, most of the data were generated using the laboratory cycle and these data have, therefore, been used in illustrating the present paper.Composition, wt-% During service, large steam turbine components experience cycles of thermal strain as a result of the temperature gradients which occur on heating and cooling during start-up and shut-down or load changes. These thermal transients are most severe at the surfaces exposed to hightemperature steam and, particularly in the region of stressconcentrating features, may result in cyclic plastic deformation. Furthermore, components operating in the creep range suffer creep damage during the on-load period.Prevention of crack formation under these combined creep-fatigue conditions is an important consideration in steam turbine practice 1 -n since inadequate allowance, in either design or operation, can lead to cracking in serv...

Reward and punishment have demonstrated dissociable effects on motor learning and memory, which suggests that these reinforcers are differently processed by the brain. To test this possibility, we use electroencephalography to record cortical neural activity after the presentation of reward and punishment feedback during a visuomotor rotation task. Participants were randomly placed into Reward, Punishment, or Control groups and performed the task under different conditions to assess the adaptation (learning) and retention (memory) of the motor task. These conditions featured an incongruent position between the cursor and the target, with the cursor trajectory, rotated 30° counterclockwise, requiring the participant to adapt their movement to hit the target. Feedback based on error magnitude was provided during the Adaptation condition in the form of a positive number (Reward) or negative number (Punishment), each representing a monetary gain or loss, respectively. No reinforcement or visual feedback was provided during the No Vision condition (retention). Performance error and event-related potentials (ERPs) time-locked to feedback presentation were calculated for each participant during both conditions. Punishment feedback reduced performance error and promoted faster learning during the Adaptation condition. In contrast, punishment feedback increased performance error during the No Vision condition compared to Control and Reward groups, which suggests a diminished motor memory. Moreover, the Punishment group showed a significant decrease in the amplitude of ERPs during the No Vision condition compared to the Adaptation condition. The amplitude of ERPs did not change in the other two groups. These results suggest that punishment feedback impairs motor retention by altering the neural processing involved in memory encoding. This study provides a neurophysiological underpinning for the dissociative effects of punishment feedback on motor learning.

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