Ultralow Cycle Fatigue Tests and Fracture Prediction Models for Duplex Stainless-Steel Devices of High Seismic Performance Braced Frames

This paper presents ultralow cycle fatigue tests and the calibration of different fracture models for duplex stainless-steel devices of high seismic performance braced frames. Two different geometries of the devices were tested in full scale under 14 cyclic loading protocols up to fracture. The imposed protocols consisted of standard, constant-amplitude, and randomly generated loading histories. The test results show that the devices have stable hysteresis, high postyield stiffness, and large energy-dissipation and fracture capacities. Following the tests, two micromechanics-based models, i.e.,the cyclic void growth model and the built-in ABAQUS ductile fracture model, were calibrated using monotonic and cyclic tests on circumferentially notched coupons and complementary finite-element simulations. In addition, Coffin-Manson-like relationships were fitted to the results of the constant-amplitude tests of the devices, and the Palmgren-Miner's rule was used to predict fracture of the devices under the randomly generated loading protocols. Comparisons of the experimental and numerical results show that the calibrated models can predict ductile fracture of the devices due to ultralow cycle fatigue with acceptable accuracy.