Issue 41

J.M. Vasco-Olmo et alii, Frattura ed Integrità Strutturale, 41 (2017) 166-174; DOI: 10.3221/IGF-ESIS.41.23 173 Figure 6 : (a) Comparison between the experimental and model predictions of plastic zone area at maximum applied load as a function of the crack length using the von Mises criterion. (b) Comparison between the experimental and CJP model predictions of plastic zone size at maximum load using both the von Mises and Tresca yield criteria. C ONCLUSIONS n the present paper a novel experimental methodology for the quantitative evaluation of the crack tip plastic zone size during fatigue crack growth has been presented. This methodology uses differentiation of the measured displacement fields to obtain strain maps that can be combined with a yield criterion to estimate the shape and size of the crack tip plastic zone. These predictions can be compared with estimates of the plastic zone size obtained from analytical models that describe crack tip displacement fields. This work indicates that the CJP model provides the best prediction of the crack tip plastic zone shape and size. It is proposed that this agreement supports the fact that the CJP model, through its basic assumptions regarding the influences of plasticity on the elastic stress fields ahead of the crack tip, is better at defining the real size of the plastic zone. A CKNOWLEDGEMENTS he current work has been conducted with the financial support from Gobierno de España through the project ‘Proyecto de Investigación de Excelencia del Ministerio de Economía y Competitividad MAT2016-76951-C2-1-P’. R EFERENCES [1] Uguz, A., Martin, J.W., Plastic zone size measurement techniques for metallic materials, Materials Characterization, 37 (1996) 105–118. [2] Steuwer, A., Edwards, L., Pratihar, S., Ganguly, S., Peel, M., Fitzpatrick, E.M., Marrow, T.J., Withers, P.J., Sinclair, I., Singh, K.D., Gao, N., Buslaps, T., Buffière, J.Y., In situ analysis of cracks in structural materials using synchrotron X- ray tomography and diffraction, Nuclear Instruments and Methods, in Physics Research Section B: Beam Interactions with Materials and Atoms, 246 (2006) 217–225. [3] Nowell, D., Kartal, M.E., de Matos, P.F.P., Digital image correlation measurement of near-tip fatigue crack displacement fields: constant amplitude loading and load history effects, Fatigue and Fracture of Engineering Materials and Structures, 36(1) (2013) 3–13. [4] Díaz, F.A., Patterson, E.A., Yates, J.R., Assessment of effective stress intensity factors using thermoelastic stress analysis, The Journal of Strain Analysis for Engineering Design, 44 (2009) 621–631. [5] Wright, S.I., Nowell, M.M., Field, D.P., A review of strain analysis using electron backscatter diffraction, Microscopy and Microanalysis, 17 (2011) 316–329. [6] Irwin, G.R., Analysis of stresses and strains near the end of a crack traversing a plate, Journal of Applied Mechanics, 24 (1957) 361–364. 0 1 2 3 4 5 6 7 8 9 10 11 12 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0 9,5 plastic zone area (mm 2 ) crack length (mm) Experimental CJP Westergaard Williams 0 1 2 3 4 5 6 7 8 9 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0 9,5 plastic zone area (mm 2 ) crack length (mm) experimental (Von Mises) CJP (Von Mises) experimental (Tresca) CJP (Tresca) I T (a) (b)