Issue 48

V. Giannella et alii, Frattura ed Integrità Strutturale, 48 (2019) 639-647; DOI: 10.3221/IGF-ESIS.48.61 639 Focussed on “Crack Paths” Multi-axial fatigue numerical crack propagations in cruciform specimens Venanzio Giannella, Michele Perrella Dept. of Industrial Engineering, University of Salerno, via Giovanni Paolo II, Fisciano (SA), Italy vgiannella@unisa.it , http://orcid.org/0000-0002-4410-9484 mperrella@unisa.it, http://orcid.org/0000-0002-3617-2328 A BSTRACT . Two cracks, initiated from the opposite tips of a central notch inclined by 45°, were considered in cruciform specimens made of Ti6246. A static load was applied to a cruciform arm while a cyclic load was applied along the other arm. Fatigue propagation of cracked specimens was performed by means of Dual Boundary Element Method (DBEM) and Finite Element Method (FEM) codes. For crack path assessment, the Minimum Strain Energy Density (MSED) and the Maximum Tensile Stress (MTS) criteria were adopted in DBEM and FEM approaches, respectively. Moreover, the J and M integrals’ formulations were used to evaluate the SIFs along the crack fronts for DBEM and FEM codes, respectively. Crack-growth rates were predicted by using a Walker law, calibrated on mode I fracture experimental data. A good agreement between numerical and experimental crack paths was obtained. K EYWORDS . Cruciform specimen; HCF; Multiple cracks; DBEM; Crack path. Citation: Giannella, V., Perrella, M., Multi- axial fatigue numerical crack propagation in cruciform specimens, Frattura ed Integrità Strutturale, 48 (2019) 639-647. Received: 30.11.2018 Accepted: 31.01.2019 Published: 01.04.2019 Copyright: © 2019 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION ver the past few decades, many efforts have been made in the modeling and simulation of three-dimensional crack propagation problems. Early works dealt with appropriate representation of intricate cracks, and calculation of Stress Intensity Factors (SIFs) along the crack fronts [1]. As crack propagation capabilities have been developed, many researchers proposed frameworks necessary to model the extending crack with minimal user workload, for instance by FEM codes, such as FRANC3D [2], CRACKTRACER3D [3], ZENCRACK [4], and by DBEM codes, such as BEASY [5]. These approaches currently are used for automatic 3D fatigue crack-growth simulations in large structures [6, 7] , in presence of residual stresses due to plasticity [8-12] and considering load spectrum effects [13]. Furthermore, hybrid FEM - DBEM submodelling procedures have been presented along the years [14-16]: these approaches couples the FEM versatility, for global problem modelling, and the higher efficiency of DBEM for crack-growth simulation in small subdomains. In the past, non-planar 3D crack-growth algorithms typically adopted 2D mode I/II crack-growth theories, well suited for many engineering applications. However, as the capability to model nonplanar cracks in complex geometries has been developed, the demand for a more detailed crack path prediction has led to use more complex propagation criteria that O