Effect of Impact Bending Rate on Fracture Behavior in Weldable Structural Steel

Abstract

Mechankal properties of weldable structural stecl (SM41) have heen studied over a wide range of nominal bending speeds ranging from 6mm/min to 40m/sec and at testing temperatures from-196 to 70°C. The results obtained are as follows,
1) The nominal skin stress of a smooth specimen increased with lowering the test temperature and increasing bending rates. Static bending of fatigue-cracked and mechanically notched specimens did not show remarkable temperature and notch root radius dependencies except at lower temperatures, while the dynamic bending gave strong temperature, notch root radius and bending speed dependencies.
2) The ratio of the nominal skin stress of notched specimens to that of smooth ones was increased with the decrease of notch root radius and showed no strong temperature dependency in static bending. In dynamic bending, the ratio was increased sharply with temperature and shifted to higher temperatures with bending speeds.
3) The effect of notch root radius was not great in fracture toughness. Plane strain fracture toughness was obtained at higher temperatures in dynamic bending than in static one.
4) The relation between cross head displacement and clip gage one was linear both for the experimental results and the finite element method.
5) The critical COD in dynamic bending might be calculated from the relation between cross head displacement and clip gage one in static test and from the experimental equation about COD and displaccment in dynamic test.
6) The critical COD was observed to be shifted to higher temperatures with increasing bending speeds.