FATIGUE CRACK PROPAGATION OF STIFFENED PANEL UNDER MULTI-AXIAL LOADING

Kurzfassung

Multi-axial stress states lead to mixed-mode stress intensity factors (SIFs) and are captured using advanced finite element methods. Analysing SIFs on a 3-dimensional stiffened panel is computationally expensive. In contrast, a homogenised 2-dimensional orthotropic plate under plane stress idealisation is less computationally expensive. There is currently no universally accepted influence coefficient that allows orthotropic SIFs to be reliably transformed into equivalent isotropic SIFs. To bridge this methodological gap, this study proposed an influence coefficient that correlates orthotropic fracture parameters of an idealised plate with isotropic fracture parameters of a stiffened panel. To develop the formulation, fatigue crack propagation was evaluated for a fully detailed 3-dimensional longitudinally stiffened panel under uniaxial tension and bi-axial tension load cases alongside its homogenised 2-dimensional orthotropic plate using the Extended Finite Element Method (XFEM) based on the linear fracture failure criterion. By integrating structural-to-material orthotropism area and inertia ratios with statickinematic equivalence principles in the derivation of the nine orthotropic elastic constants, this coefficient effectively acted as a structural localisation factor. The outcome of this study allows engineers to interpret fatigue fracture parameters from 2-dimensional orthotropic plates, thereby improving computational efficiency without sacrificing accuracy.