Investigation of Cumulative Fatigue Damage Through Sequential Low Cycle Fatigue and High Cycle Fatigue Cycling at High Temperature for a Type 316LN Stainless Steel: Life-Prediction Techniques and Associated Mechanisms

Fatigue design curve under LCF as well as combined LCF and HCF regime at 923 K in a type 316LN stainless steel

“…Cylindrical fatigue specimens with a gauge length of 25 mm and a gauge diameter of 10 mm (Figure ) were used for both LCF and HCF testing. LCF tests were conducted at 923 K in air under fully reversed total axial strain control mode ( R = −1) using a triangular waveform as per ASTM E‐606, at different strain ranges ( Δε t ) varying from 0.5% to 0.12%, employing a fixed strain rate of 3 × 10 −3 s −1 . Similarly, HCF data were generated on virgin material at 923 K at different stresses using an R ratio of −1.…”

“…Prior LCF deformation was carried out at various Δε t in the range 0.5% to 0.12% for different life fractions varying from 20% to 80%. The pre‐exposed specimens were subsequently cycled under HCF to failure at a stress slightly above the endurance limit where finite failure was observed ( R = −1) . Three specimens were tested at each HCF stress level to account for the inherent scatter in HCF, and the average value is used.…”

“…To achieve this goal, the investigation was primarily carried out at 923 K. The inner vessel of the SFR experiences a peak operating temperature of about 823 K. However, during transients, operating temperature is expected to increase to 923 K. Hence, 923 K was chosen as the testing temperature in the experiments pertaining to LCF‐HCF interaction. A detailed study has already been carried out by the authors on the damage evolution under LCF‐HCF interaction at 923 K in type 316LN austenitic stainless steel (the main structural material for inner vessel components in SFRs) through sequential application of LCF and HCF loads . Traditionally, strain‐based approach (total strain life curve) devised by Coffin‐Manson is employed for design against LCF, particularly when the components are subjected to cyclic thermal stress.…”

“…Albeit Miner's linear damage rule as a stress‐based approach is very popular for life prediction under combined loadings, the same has inherent limitations with respect to predicting the load sequence effects on damage accumulation and resultant cyclic life . The authors have established through their previous studies that damage mechanisms are highly complex under combined loading involving LCF and HCF particularly at elevated temperature like 923 K, wherein significant deviation from the Miner's rule has been noticed . To take this into account, Manson's damage curve approach (DCA) was suitably modified, for predicting the remnant HCF life .…”

“…A detailed study has already been carried out by the authors on the damage evolution under LCF-HCF interaction at 923 K in type 316LN austenitic stainless steel (the main structural material for inner vessel components in SFRs) through sequential application of LCF and HCF loads. 5,6 Traditionally, strain-based approach (total strain life curve) devised by Coffin- Manson 7,8 is employed for design against LCF, particularly when the components are subjected to cyclic thermal stress. Hence, LCF tests are carried out under strain-control mode where the specimen is subjected to gross plastic deformation with cyclic life not exceeding 10 4 cycles.…”