Brittle-failure resistance in a thick-walled construction

Abstract

1. Steel 15Kh2NMFA has a high resistance to brittle failure in large sizes. Specimens of cross section 150 × 600 mm and disc models of cross section 150 × 650 mm with sharp concentrated defects of depth 30 mm fail at stresses approximately equal to the ultimate strength. The failure stresses decrease as the defect size increases. Under biaxial strain (accelerated discs), the fall in the failure stress as the defect size increases is more pronounced than it is in uniaxial stretching. 2. Subcritical defect growth is observed in all the specimens; the onset of this growth (initiation of crack growth) has been determined by the electrical potential method, from the acoustic emission, and from the onset of macroplastic strain. The results are in good agreement. The subcritical growth decreases as the defect size rises. 3. To estimate the strength of a thick-walled construction with defects, one should use the failure diagram showing the relationship between the failure stress and the defect size. This diagram has an upper bound represented by the ultimate strength of the material, and on the right is bounded by the critical stresses calculated from the force criterion for the linear mechanics of failure Kjc. 4. The theoretical evaluation of structure strength from this failure diagram corresponds closely to the experimental data on large specimens and disc models in the regions of brittle and quasibrittle failure, and it gives a safety margin.