Litʹë i Metallurgiâ (Oct 2019)
The ways to ensure fatigue strength of cold-formed rebars. Foundry production and metallurgy
Abstract
To ensure safe operation of buildings and structures from reinforced concrete, European norms set requirements for its fatigue strength (resistance). Tests are carried out with oscillation swing amplitude 2sa from 150–200 MPa. Rebar shall withstand from 1 to 2 mln. cycles.The analysis of causes which decrease the fatigue strength of cold-formed steel is made in the article. Fatigue strength is a lot affected by surface defects and stress concentrators. Filler transition in the point where transversal rib crosses a rebar body becomes as a rebar stress concentrator. To detect details of early breakage, analysis the condition of fracture in the area of thickened (marking) ribs was made. Sequence of rebar breakage was established as well as the initial point of a crack creation was detected. This fracture is characterized as a fatigue one, with clear zones of fatigue fracture having fine-grained surface and static fracture zone– the rest of section with fibrous structure. While applying a bar mark, smoothness of filler transition was disturbed in the crossing point where transversal rib crosses a rebar body, and this action caused decrease of fatigue strength of cold-formed rebar.The article describes research on development of requirements for rolling tools used in production of cold-formed rebars.Use of information given in this article during design, purchasing and manufacture of the equipment will allow to minimize factors which have negative influence on rebar’s fatigue test results.
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