PSI - Issue 5

Behzad V. Farahani et al. / Procedia Structural Integrity 5 (2017) 920–927 Behzad V. Farahani et al./ Structural Integrity Procedia 00 (2017) 000 – 000

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5. Conclusions

In the framework of the linear fracture mechanics, this preliminary work addresses the experimental measurement of the mode I stress intensity factor (SIF) for a standard compact tension specimen during a uniaxial fatigue crack growth test. A non-contact full-field optical technique so-called “ Digital Image Correlation ” was used to measure the strain variations on the specimen surface. Using the strain field captured fromDIC analysis, the stress field is therefore evaluated relying on the 2D plane stress formulation of Hooke’s law. Considering the obtained stress data together with William’s series expansion, the mode I stress intensity factor is calculated through a numerical overde terministic algorithm for several crack lengths. Besides, the fracture model is simulated with numerical methods; FE and RPIM meshless methods, to validate the SIF and strain variation in front of the crack tip obtained from DIC experimental test. The geometrical and mechanical characteristics, in addition to essential boundary conditions, are fully defined in accordance with the experimental data. Concerning the FE analysis, the 2D linear fracture model is solved in ABAQUS©. So, the problem was elasto statically analyzed for different crack lengths to obtain internal variables and SIF range assuming the strain energy release rate criterion in the presence of integral contours. Likewise, the RPIM meshless method formulation was considered to analyze the present model. As outcome, the polar coordinates of the points located in the interest cracked region and their stress states were determined. In accordance with these results, the SIF range was thus calculated using the same overdeterministic algorithm used in DIC solution procedure. An acceptable agreement amongst the reference solution reported by ASTM E647, experimental DIC and numerical approaches was attained. Consequently, the obtained results proved that the supporting numerical methodology was robust and feasible, and the success of the proposed model was thereby accomplished. The first author truly acknowledges the funding provided by Ministério da Educação e Ciência, Fundação para a Ciência e a Tecnologia (Portugal), under grants PD/BD/114095/2015 and SFRH/BPD/111020/2015. Dr. Moreira acknowledges POPH - QREN-Tipologia 4.2 - Promotion of scientific employment funded by the ESF and MCTES. Authors gratefully acknowledge the funding of Project NORTE-01-0145-FEDER-000022 - SciTech - Science and Technology for Competitive and Sustainable Industries, cofinanced by Programa Operacional Regional do Norte (NORTE2020), through Fundo Europeu de Desenvolvimento Regional (FEDER). References ASTM International, 2015. ASTM E647 - 15 Standard Test Method for Measurement of Fatigue Crack Growth Rates. In United States: ASTM International, p. 43. Available at: http://www.astm.org/Standards/E647. Belytschko, T. & Black, T., 1999. Elastic crack growth in finite elements with minimal remeshing. International Journal for Numerical Methods in Engineering , 45(5), pp.601 – 620. Available at: http://doi.wiley.com/10.1002/%28SICI%291097-0207%2819990620%2945%3A5%3C601%3A%3AAID NME598%3E3.0.CO%3B2-S [Accessed December 2, 2016]. Belytschko, T., Gu, L. & Lu, Y.Y., 1994. Fracture and crack growth by element free Galerkin methods. Modelling and Simulation in Materials Science and Engineering , 2(3A), pp.519 – 534. Available at: http://stacks.iop.org/0965-0393/2/i=3A/a=007?key=crossref.c94132e9dd12cb997fcd04d1330021cf [Accessed November 29, 2016]. Belytschko, T., Lu Y, Y. & Gu, L., 1994. Element free Galerkin methods. Int. J. Methods Eng. , 37, pp.229 – 256. Byskov, E., 1970. The calculation of stress intensity factors using the finite element method with cracked elements. International Journal of Fracture Mechanics , 6(2), pp.159 – 167. Available at: http://link.springer.com/10.1007/BF00189823 [Accessed November 29, 2016]. Carpinteri, A. & Paggi, M., 2007. Numerical analysis of fracture mechanisms and failure modes in bi-layered Acknowledgements