CHARACTERISTICS OF STAGES (PERIODS) OF LOAD-EXTENSION CURVE OF STRUCTURAL STEELS

Specimens of armco iron and steels 09GS and 37G2S possessing strongly different load-extension diagrams are studied. The sigma = f (delta) curves are divided into regularly alternating periods, i.e., linear, power within the uniform stage, and I, II, III in the lumped stage. Each period is characterized by the yielding parameter (YP), plasticity components (elongation delta(i)), initial stress sigma(i), and rate of growth/decrease of the stress (Delta sigma/Delta delta)(i). Analysis of the YP is used to compare the periods in differently hardened specimens. It is shown that the combination of these periods is responsible for the standard mechanical properties of the specimens. The values of the YP are used to trace the relation between the ductility and the crack resistance and to show that the stress sigma(II) and the elongation delta(IIs)(l) at the start of period II of the concentrated stage may be treated as criteria of crack resistance.