Abstract
In the last few decades, great effort has been spent on advanced material testing and the development of damage models intended to estimate the ductility and fracture of ductile metals. While most studies focused on static testing are applied at room temperatures only, in this paper, multiaxial tests have been executed to investigate the effects of dynamic action and temperature on the mechanical and fracture behavior of an API X65 steel. To this end, a Split Hopkinson Bar (SHB) facility for dynamic tests, and a uniaxial testing machine equipped with a high-temperature furnace, were used. Numerical simulations of the experiments were setup for calibration and validation purposes. Based on the experimental results, the Johnson–Cook and Zerilli–Armstrong plasticity models were first tuned, resulting in a good experimental–numerical match. Secondly, the triaxiality and Lode angle dependent damage models proposed by Bai–Wierzbicki and Coppola–Cortese were also calibrated. The comparison of the fracture surfaces predicted by the damage models under different loading conditions showed, as expected, an overall significant increase in ductility with temperature; an appreciable increase in ductility was also observed with the increase in strain rate, in the range of low and moderate triaxialities.
Highlights
Over the years, the requirements, in terms of mechanical performance, of engineering materials have become increasingly more stringent in order to meet the high safety and quality standards expected of modern products and processes
The tests are conducted with control of displacement, and with constant speeds of 1 mm/s (RB), 0.25 mm/s (RN2) and 0.5 mm/s (PS), which are conditions that could be regarded as quasi-static
Two temperatures are tested, based on results from the literature: 700 °C, which falls in the middle of the typical warm temperature range (600– 800 °C) for steels, and 600 °C, which is regarded by some authors [44] as the best choice
Summary
The requirements, in terms of mechanical performance, of engineering materials have become increasingly more stringent in order to meet the high safety and quality standards expected of modern products and processes In this scenario, in addition to the identification of the elastic limits related to a safe design under normal operation conditions, it is mandatory to investigate the material’s elasto-plastic behavior, ductility, and ultimate strength under all possible operating conditions. This, in turn, would permit us to simulate material behavior at different temperatures and dynamic conditions, and allows the identification of the evolution of the state of stress, plastic strain accumulation and strain at fracture in the material under test conditions This information is used to calibrate the selected damage models, which, once proven to be suitable for use in predicting failure in these new conditions as well, will provide a picture of material ductility and ultimate strength at different temperatures and strain rates. The differences in material behavior when moving from static to high strain rate loading conditions, and from room temperature to warm temperatures, are quantified and discussed, along with an assessment of the accuracy and limitations of the selected plasticity and damage formulations
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