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P. Lopez-Crespo et alii, Frattura ed Integrità Strutturale, 25 (2013) 153-160; DOI: 10.3221/IGF-ESIS.25.22 159 C ONCLUSIONS sing very high spatial resolution (60  m laterally) we have been able to explore the crack opening elastic strains in the vicinity of a fatigue crack before and after an overload event. We have followed the crack until it is 1mm beyond the overload location. It is clear that the peak tensile strain drops dramatically and slowly recovers as the fatigue crack works its way through the compressively stressed plastic zone caused by the overload event. That this is an elastic effect is demonstrated by the similarity of the elastic strain changes before and just after overload between K max and K min . By superimposing the crack tip strain fields for the crack tip at different stages of growth there is a suggestion that for baseline fatigue there is both a compressive stress just ahead of the crack due to plasticity and behind the crack due to crack face closure. There is no evidence of the later after a small number of cycles in agreement with surface digital image correlation measurements that indicate no closure in this regime. Once the crack-tip has progressed significantly past the overload event there is strong evidence that the crack faces contact in the region of the overload event (though not in the immediate vicinity of the current locations of the crack tip) even when the crack has travelled 1mm beyond the overload location. Of course it is extremely difficult to scan a 60  m beam along the crack plane, experiments are now being undertaken to provide full 2D maps of the crack tip stress field to provide more definitive evidence.  A CKNOWLEDGEMENTS e acknowledge ESRF for the use of facilities and the EPSRC for funding through grant EP/F028431/1.  R EFERENCES [1] Sadananda, K., Vasudevan, A.K., Holtz, R.L., Lee, E.U., Analysis of overload effects and related phenomena. International Journal of Fatigue, 21 (1999) S233-S246. [2] Alizadeh, H., Hills, D.A., de-Matos, P.F.P., Nowell, D., Pavier, M.J., Paynter, R.J., Smith, D.J., Simandjuntak, S., A comparison of two and three-dimensional analyses of fatigue crack closure, International Journal of Fatigue29 (2007) 222-231. [3] Steuwer, A., Edwards, L., Pratihar, S., Ganguly, S., Peel, M, Fitzpatrick, M.E., 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, B 246 (2006) 217-225. [4] Steuwer, A., Rahman, M., Shterenlikht, A., Fitzpatrick, M.E., Edwards, L., Withers, P.J., The evolution of crack-tip stresses during a fatigue overload event, Acta Materialia, 58 (2010) 4039-4052. [5] Croft, M., Shukla, V., Jisrawi, N.M., Zhong Z., Sadangi, R.K., Holtz, R.L., Pao, P.S., Horvath, K., Sadananda, K., Ignatov, A., Skaritka, J., Tsakalakos, T., Mapping and load response of overload strain fields: Synchrotron X-ray measurements. International Journal of Fatigue, 31 (2009) 1669–1677. [6] Kelleher, J.F., Lopez-Crespo, P., Yusof, F., Withers, P.J., The use of diffraction to study fatigue crack tip mechanics. Materials Science Forum, 652 (2010) 216-221. [7] Lopez-Crespo, P., Withers, P.J., Yusof, F., Dai, H., Steuwer, A., Kelleher, J.F., Buslaps, T., Overload effects on fatigue crack-tip fields under plane stress conditions: surface and bulk analysis, Fatigue and Fracture of Engineering Materials and Structures, 36 (2013)75-84. [8] Robertson, I.M., Measurement of the effects of stress ratio and changes of stress ratio on fatigue crack growth rate in a quenched and tempered steel. International Journal of Fatigue, 16 (1994) 216-220. [9] Anderson, T.L., Fracture Mechanics, Fundamentals and Applications, (2005). [10] Murakami, Y., Stress Intensity Factors Handbook. Oxford: Pergamon Press, (1987). [11] Stoychev, S., Kujawski, D., Methods for crack opening load and crack tip shielding determination: a review. Fatigue and Fracture of Engineering Materials and Structures, 26 (2003) 1053-1067. U W