Conditions for notch strength to be higher than static tensile strength in high-strength ductile cast iron

摘要

In this study, notch strength sigma(notch)(B) was studied for a wide range of testing speed and temperature in comparison with the static tensile strength at room temperature sigma(smooth)(B, RT). High-speed tensile tests were conducted on high-Si ductile cast iron, conventional ferrite-pearlite ductile cast iron, and fully pearlitic ductile cast iron at a stroke speed ranging between 8.5 x 10(-3) and 2.7 x 10(2) mm/s (strain rate of 2.1 x 10(-4) and 1.8 x 10(1) s(-1)) and temperature ranging between -180 degrees C and 22 degrees C. Then, sigma(notch)(B) and sigma(smooth)(B, RT) were compared in terms of the strain rate-temperature parameter R = T ln (A/epsilon) to evaluate the combined influence of the strain rate epsilon and temperature T. It was found that the notch strength sigma(notch)(B) can be expressed as a unique master curve in terms of R parameter for each material. Then, a notch-strengthening threshold criterion R = R-th was proposed to describe the lowest service temperature and highest strain rate that can be applied to the structural components. Under the condition R = R-th, sigma(notch)(B) is always larger than sigma(smooth)(B, RT), and therefore, notched components can be used safely. In other words, if R = R-th, sigma(smooth)(B, RT) can be used to evaluate the notched components in machine design to prevent instantaneous fractures.