Scale Effects in Notch Brittleness

Abstract

The research reported herein is an investigation of the scale effects on notch brittleness of mild steel specimens having a geometrically similar shape. The specimens were machined from the same rimmed steel, whose roll thickness was 45mm. The shape of specimens is shown in Fig. 1. The cross section of the smallest size specimen is 10 mm × 10 mm; notch depth is 2 mm ; notch shape is 45°V ; and notch radii are 0.05, 0.1, 0.2, 0.4, 0.8 and 1.6 mm respectively. The middle size specimen is 21 × 21 mm in cross section, and the largest one in 42 mm × 42 mm in cross section.
The test was made by slow bending, under the condition of same strain rate. The transition temperatures are shown in Fig. 8. The smallest one has a relatively low transition temperature, but for the specimens above the 21 mm size the transition temperatures are nearly equal.
The scale effects on the maximum breaking stress (nominal) and yield stress are shown in Fig. 11. As shown in the figure the maximum breaking stress gradually decreases with increase of specimen.size, but the yield stress remains nearly constant.
The absorbed energy in relation to the specimen size is shown in Fig. 13; the absorbed energy in shear fracture increases with specimen size in cubic proportion, while the energy in brittle fracture is proportional to the 2.5 power. The adsorbed energy per unit volume of specimen is shown in Fig. 14. In this figure the energy in brittle fracture gradually dereses with increase of specimen size.