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Rp - limit of proportionaltty). Hooke s law is valid Ra - limit of elaslicity. materiał is atill elastic without permanent strains.

ReH, Red - upper plastic yield point) and bottom piastic yield point) Permanent strains are present. Ludersa lines can be noticed on the specimen surface

Beyond the plastic strains fiat surface the hardening can be noticed that is the resutt of crystalline structure rebuilding. Maximum of the curve Rm is tensile strength limit and is denoted as f_u in the EC-3 codę. For the higher values of stresses we can observed the neck. After that the break of the specimen takes place