Uniaxial Ratchetting And Creep Of 316L Stainless Steel

The ratchetting of materials corresponds to progressive inelastic deformation under cyclic stressing. The ratcheting effect has arisen abroad recognition by scholars and the research on the ratchetting has come a hot direction. The creep of metalic materials corresponds to progressive inelastic deformation under loading with invariable stress. The intrinsical relationship between ratcheting and creep begin to be concerned in academe.A series of ratchetting and creep experiments for 316L stainless steel were carried out, the characters of progressive inelastic deformation of the material in the high-cycles were investigated systematically, the law that ratchetting strain was controlled by peak stress, as well as the relationship between ratchetting strain and creep strain was been studied. Moreover, the signal channel extending technique was developed. The following research findings were obtained:(1) After hundrds of load cycles ,the ratchetting strain of SS316L would keep on growing in the following 10000 cycles, if the peak stress is higher than the ratchetting threshold stress;the higher the peak sterss is, the less cycles materials requires to reach saturated state;the greater amplitude stress would postpone the progressing inelastic deformation;(2) The ratchetting effect of 316L steel is not remarkable at 350℃;(3) The saturated ratchetting strain is controlled by peak stress under cyclic stressing, and then a parabola model named as SRM(MAX) was presented to use for predicting the strain of the material after high number of stress cycling.(4) The heat treatment process would resume the ratchetting capability of 316L steel completely, ignoring the damage in the cyclic deformation;(5) In a large range of the ratio of amplitude stress to peak stress, the amplitude stress history does not affect the rule that peak stress dominate the saturated ratchetting strain of 316L steel;on the other hand, when both of peak stress and the ratio become higher, the single parameter character of peak stress will be altered, because of fatiguedamage caused by great amplitude stress;a modified SRM(MAX) model whit peak and amplitude stress limits has been represented;(6) A series of ratchetting and creep experiments controlled by true stress were carried out, assisted by the developed software by author, the results show that: the ratchetting experiment results of 316L steel controlled by true stress accord with that controlled by engineering stress;and also, the control mode does not affect the results of creep experiment, the relationship between the 10000s creep strain and creep stress can be described by a parabola, then a CEM model that predicts the creep-evoluated rules in the first and second stage of 316L steel was proposed;(7) Comparing with ratchetting deformation, the creep deformation is associate whit the load hours and load history;based on the cumulative inelastic strain of ratchetting and creep, a C-SRM model and C-CDM model which can reflect the substance of ratchetting and creep cumulative inelastic deformation has been proposed;(8) The curves of the rachetting-evoluated strain can be computed by the creep-evoluted model, and the computed results accord with experiment results well, so, in the case of peak stress dominanting the saturated ratchetting strain, the ratchetting deformation is actually caused by the instantaneous creep under the cyclic stress loading, further more the inherent relationship between ratchetting and creep of the materials has been expressed;(9) Baseed on the exploitation of communications interface, calibrating device and method, the function of the software, a signal channel extending technique of MTS TestStar II was developed, with which, kinds of functions included the applications of MTS standerd transducers, A/A and P/A elements made in China into MTS TestStarll are realizable, it extended the testing ability of MTS effectively, also is helpful to reduce the cost of equipments servicing and testing.