Application of the Effective Strain Energy Density Factor in the Estimation of the Fatigue Life of Notched Specimens

 

Daniela Ristić,

Marko Bojanić

 

Life estimation and behavior of machine elements with initial cracks under cyclic loads is one of very important engineering problems. It is possible to considered structural elements with various shapes and crack dispositions as well as with various crack propagation models. The calculation of the stress intensity factors K, crack propagation and life of structural elements are of utmost importance in this analysis. The estimation of the life of structural elements is carried out under cyclic loads with a constant amplitude. This paper includes the comparisons of the numerical finite element method (FEM), an analytical one and the already available test results for the cylindrical thin-walled pipe of the radius R and the thickness t. The pipe is loaded by the internal pressure p_c. Critical pressure is determined using the strain energy density theory (SEDT) [1]. The additional feature of the S_c theory is that a single parameter can simultaneously determine the fracture toughness of the material and the direction of the crack growth initiation. Since a fatigue load cycle is characterized by the mean stress and stress range, the Paris rule may not be adequate to analyse the crack growth behavior because it only takes into account one loading parameter. To solve this problem a modified version SEDF based on a so-called effective strain energy density factor [2] will be used. It is intended to verify the applicability of empirical models based in experimental evidence.

Key words: material fatigue, crack, crack propagation, life, energy density theory, finite element method (FEM).