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J. Tong et alii, Frattura ed Integrità Strutturale, 25 (2013) 44-49 ; DOI: 10.3221/IGF-ESIS.25.07 48 (a) (b) Figure 4: Strain responses at (a) R 2 and (b) R 4 with the number of cycles for the four test series (Fig. 1), comparison of the results from the DIC and the FE analysis. C ONCLUSIONS e report the first experimental evidence of the near-tip strain evolution as captured by the Digital Image Correlation on a compact tension specimen of stainless steel 316L. The evolution of the near-tip strains with loading cycles was monitored at selected load levels whilst the crack tip remains stationery. The results clearly show that strain ratchetting occurs with cycle, and is particularly evident close to the crack tip and under higher loads. Finite element analyses have also been carried out, and the results compare favourably with those measured at a distance about the grain size. R EFERENCES [1] Tong, J., Zhao, L.G., Lin, B., Ratchetting strain as a driving force for fatigue crack growth, Int. J. Fatigue, 46 (2013) 49–57. [2] Zhao, L.G., Tong, J., A viscoplastic study of crack-tip deformation and crack growth in a nickel-based superalloy at elevated temperature, J. Mech. Physics Solids, 56 (2008) 3363-3378. [3] Zhao, L.G., Tong, J., Byrne, J., The evolution of the crack tip stress-strain fields and plasticity induced crack closure revisited, Fatigue Fracture Engng. Mater. Struc., 27 (2003) 19-29. [4] Tong, J., Cornet, C., Lin, B., Zhao, L.G., Unpublished results, (2012). [5] http://www.correlatedsolutions.com/index.php/products/vic-3d-2012/microscopy , (2012) [6] McNeill, S.R., Peter, W.H., Sutton, M.A., Estimation of stress intensity factor by digital image correlation, Engineering Fracture Mechanics, 28(1) (1987) 101–112. [7] Durig, B., Zhang, F., McNeill, S.R., Chao, Y.J., Peters III, W.H., A study of mixed mode fracture by photoelasticity and digital image analysis, Optics and Lasers in Engineering, 14(3) (1991) 203–215. [8] LaVision GmbH, StrainMaster Mannual DaVis 8.1, Gottingen, Germany, (2012). [9] ABAQUS 6.8, Hibbitt Karlsson and Sorensen Inc, Providence, RI, (2009). [10] Lemaitre, J., Chaboche, J.L., Mechanics of Solid Materials, Cambridge University Press, (1990). W