Effect of step-wise change of stress on primary creep of structural steel

The interrelation of primary creep deformation under step-wise varying stresses and constant stresses has been studied experimentally using the SM50A structural steel in the temperature range of 400 to 5500C. The testing program was directed towards investigating the creep law under varying stresses, especially at the primary stage of creep. The results of the varying stress tests were compared with the calculated results due to the creep laws presented by authors, i.e. the modified strain-hardening law and two other typical creep laws of the strain-hardening and time-hardening law. The results indicate that, under the test conditions in this study, primary creep strains under varying stresses could be estimated with good precision from the results of constant stress creep tests and stress-strain curves by using the modified strain hardening law in which not only the effect of creep strain but also plastic strain has been taken into account. (author)