Deformation capacity of 400 N/mm2 class structural steel under extremely large strains

Abstract

To provide qualitative database for further studies regarding the evaluation of the cyclic deformation capacities of 400 N/mm2 class structural steel up to the maximum strength as well as the complete fracture, strain-based cyclic loading tests were performed in the low and extremely low-cycle fatigue regimes. Thirty-nine specimens were employed and tested with strain amplitudes in the range from ±2% to ±12%. By using three different specimen configurations made from three different lots of steel materials, and by performing axial cyclic tests (starting with tensile and compressive loads), the influences of different lots, specimen configurations, and different initial loading directions on the strain-life curve could be examined. The experimental results indicated that cyclic hardening behaviors of all specimens occurred in the first several cycles, while specimens tested with smaller strains (3% or below) stabilized until failure. However, specimens fractured in a ductile manner without achieving stabilization when they were subjected to large strain tests. The strain-life curve (up to failure) exhibited a linear relationship with strain amplitudes up to 10%. At larger strain amplitudes, the cyclic deformation capacity of the steel material reached its peak and subsequently became nonlinear. Nevertheless, the strain-life curves up to peak cyclic stress of all specimens show a continuous linear relationship with strain amplitudes up to 12%.