Effect of localized strain on fracture of high-strength structural steel with varying stress stiffness

The paper studies the mechanical properties and configuration of plastic zones in notched high-strength structural steel under tension. Quantitative analysis of the plastic zones is made by constructing strain intensity distribution patterns with the use of the television-optical measuring complex TOMSC. Fracture associated with plastic flow is analyzed by comparing fractographs and distributions of strain characteristics. It is found that the fracture originates in a region with maximum strain intensity. It is shown that the mechanisms of plastic flow in high-strength steel specimens with Pi < 1.58 and Pi > 4.65, where Pi is the index of initial stress stiffness, differ considerably. It is demonstrated that the high-strength steel specimens arc fractured by quasibrittle mechanisms; however, ductile micromechanisms through pore nucleation and growth remain operative at all stages of fracture.