PSI - Issue 42

Hasan Saeed et al. / Procedia Structural Integrity 42 (2022) 967–976 Hasan et al./ Structural Integrity Procedia 00 (2022) 000 – 000 3 Based on the validity ranges reported in literature, the BFS compliance solution for SENB-4P specimens is seen to be lacking for relatively short cracks, i.e. / ≤ 0.15 . The main objective of this work is to implement finite element simulations to develop a BFS solution that allows to monitor a wider range of cracks in SENB-4P specimens. Besides, the developed BFS compliance curve is to be validated by dedicated fatigue experiments using the DCPD technique for crack monitoring. 2. Finite element model and simulations 2.1. Modelling In this study, a series of FE simulations was used to calculate the linear elastic strain response of an SENB-4P specimen subjected to 4-point bending. Specimens with global geometry according to ISO 12108 and with 16 different values of normalized crack length, / ranging from 0.05 to 0.6, were modelled. Fig. 2 shows the mesh generated over the specimen and near the crack tip. The crack is modelled as an internal edge partition embedded inside a face, labelled as a seam crack in ABAQUS/CAE 2021.HF3 software. Elastic material properties were considered with Poisson's ratio =0.3 and Young's modulus =207GPa, typical for structural steel S355. A so-called “spider - web” mesh configuration is implemented around the crack tip; this consists of concentric rings of C3D20 quadrilateral elements that are focused toward the crack tip. This allows a smooth transition from a fine mesh at the tip to a coarser mesh moving away from the tip (thus allowing for feasible computational times without loss of accuracy) (Verstraete et al., 2015). The loading parameters are based on a nominal stress range ( ) of 300 MPa and a load ratio = / of 0.1. The strain range ( ) at the back-face corresponding to the applied was extracted for varying crack length ratios / . In this analysis, strain is extracted at the centre of the back-face of the specimen and averaged over the area of a strain gauge attached to the specimens in the experimental study. 969

Fig. 2. Diagram illustrating a typical mesh used in finite element analysis and region where back-face strain is calculated. The strain range at the back-face calculated from the FE simulations is shown in Fig. 3 for different / ratios.