Characterization of the biaxial fatigue behaviour on medium carbon steel using the strain-life approach

Abstract

This study aims to investigate the fatigue behaviour and determine the fatigue life prediction under biaxial loading. Fatigue tests were performed according to ASTM 2207-02 and the values of tensile stresses are selected from the ultimate tensile strength which is 0.5 Su, 0.6 S_u, 0.7 Su, 0.8 S_u and 0.9 S_u, while the torsion angle representing the shear stresses acting was set at 15 degrees. The biaxial fatigue test was conducted using a combination of two types of stresses acting on the same frequency, namely 1 Hz, on smooth specimens made from medium carbon steel. The biaxial fatigue lives of the specimens are recorded when the specimen has completely fractured. The results indicate that the observed fatigue lives are in good agreement with the predicted lives by using the Coffin–Manson, Morrow, and Smith–Watson–Topper strain-based models. Mohr’s circle approach was used to determine the maximum shear stress and principal normal stress. The maximum shear stress increased from 457 MPa to 486 MPa with the increment of principal normal stress from 612 MPa to 767 MPa. The principal stresses, maximum shear stresses, and energy dissipated were used to explain and describe the behaviour of biaxial fatigue. Both stresses are inversely proportional to the fatigue life. Meanwhile, the energy is linearly proportional to the stress applied, where the values increase in the range 500 kJ/m³ to 605 kJ/m³ . Thus, the basic understanding of the material behaviour may be used in the processes of declaring component service lives and the fatigue life prediction of a particular automotive component. Therefore, the cost incurred can be reduced for the development process in material engineering.