High-Strain Low-Cycle Fatigue Behavior of Thermomechanically Treated Rebar

Low-cycle fatigue (LCF) behavior of a thermomechanically treated Fe 500 grade rebar has been evaluated under high-strain ranges to understand its seismic performance. The total strain-controlled LCF tests have been performed at five different strain (1.0, 2.0, 3.0, 4.0 and 5.0%) ranges at ambient temperature until failure maintaining a constant true strain rate of 1 × 10−3 s−1 and a fixed strain ratio of − 1. Fatigue data have been analyzed following strain-life relationship; while, macro- and micro-features of the failed specimens have been critically examined under SEM. Evaluation of fatigue behavior has been supplemented by microstructural characterization apart from measurements of hardness and tensile property. Continued cyclic softening has been observed till failure, and the cyclic yield strength is found to be significantly lower than the monotonic one. Cross-sectional microhardness measurements of rebar before and after fatigue reveals significant reduction in hardness specifically in the rim region with tempered martensite microstructure. The strain-life relationship accurately predicts the cyclic plastic behavior of the selected rebar which also exhibits non-Masing behavior. The fatigue crack is always found to initiate from the transverse rib root and propagates along the rim region following the rib.