Analytical and Experimental Assessment of Ultimate Tensile Strength of a Hardened Layer on a Material Surface.

Ultimate tensile strength of a hardened layer on a material surface is studied analytically and experimentally with the application of the finite element method and the rule of mixtures, when a specimen with a hardened surface layer is viewed as a composite material consisting of a matrix and hardening layer. It has been found that the application of both methods gives close ultimate tensile strength values for the hardened surface layer. Particularly, for a surfacehardened medium-carbon (0.51 wt% C) structural steel, the ultimate tensile strength of the hardened surface layer is 2700 MPa for the finite element method and 2671 MPa for the rule of mixtures. The obtained results testify to the possibility of determining the ultimate tensile strength of a hardened layer on a material surface by standard mechanical testing for uniaxial tension. The distribution of normal stresses has been determined in a bulk specimen and in a surfacehardened specimen. The presence of a 30 μm thick non-gradient hardened layer on a material surface is shown to cause a strong local stress concentration resulting from the effect of primary mesoconcentrators arising at the site of external load application and by the difference in the mechanical properties of the base material and the hardened surface layer. [ABSTRACT FROM AUTHOR]