Issue 41

A. S. Cruces et alii, Frattura ed Integrità Strutturale, 41 (2017) 54-61; DOI: 10.3221/IGF-ESIS.41.08 55 or retardation [13,14] or mixed-mode local changes in the volume [15]. However, uniaxial approach does not represent the real world scenario and computation of fatigue life thru these approach often results either in under prediction or over prediction of fatigue life for the machine component. Because of the complexities and computational cost involved with the multiaxial fatigue tests, very limited amount of fatigue data are publicly available [16]. Among several other fatigue models, critical plane-based fatigue models provide more accurate prediction of fatigue lives. Critical plane-based fatigue models are based upon the determination of the location of fatigue crack initiation and microcrack –propagation [17]. The damage is computed at the plane where crack initiates, and this plane is called critical plane, however; the definition of critical plane is still controversial among the fatigue researchers. Some researchers define this plane as the plane of maximum fatigue damage, whereas other group of researchers believe that considering the plane of maximum shear stress as critical plane will be more logical and computationally cheaper. Fatigue data from the multiaxial test on St52-3N steel specimen have been analyzed in this paper by using new Fatemi- Socie model [18] and Suman-Kallmeyer model [19]. It is well known fact that the shear stresses at the critical plane provokes the fatigue crack initiation whereas, presence of tensile stress in combination of shear stress creates condition for the microcrack to propagate. Both of the damage parameters [18,19] discussed in this paper consider the interaction of normal and shear stress at the critical plane. Both of these damage parameters [18,19] have been used to predict the fatigue life of the test specimen, and the correlation between experimental and predicted fatigue life has been analyzed. M ATERIALS AND METHODS aterial and test data have been taken from the previous biaxial fatigue test program at the University of Malaga [20]. The material that has been considered for this paper is St52-3N. The chemical composition for this steel is: 0.17% C, 1.235% Mn, 0.225% Si, 0.010% P, 0.0006% S, 0.032% Al, 0.072% Cr, 0.058% Ni and 0.016% Mo. This is a low carbon steel, and has been widely used in the structural applications in the construction, manufacturing, ship building and offshore industries [21] that combines good fatigue resistance with low environmental impact for applications where no energy is consumed during the use phase of the component [22]. Monotonic tension, compression and torsion tests were conducted to evaluate the monotonic properties of the St52-3N steel (Tab. 1). Tension tests were conducted on the solid specimens, whereas, compression and torsion tests were conducted on the tubular specimens [23]. Fig 1 shows the geometry and dimensions of the tubular specimen. Yield stress, σ y 386 MPa Ultimate tensile stress, σ u 639 MPa Young’s modulus, E 206 GPa Shear modulus, G 78 GPa Critical buckling stress, σ cr 348 MPa Table 1 : Monotonic properties of St52-3N steel. Figure 1 : Geometry of the tubular hollow specimen used in the experiments. All dimensions are in mm. M