Issue 33

P.J. Whithers et alii, Frattura ed Integrità Strutturale, 33 (2015) 151-158; DOI: 10.3221/IGF-ESIS.33.19 151 Focussed on characterization of crack tip fields 2D mapping of plane stress crack-tip fields following an overload P. J. Withers School of Materials, Grosvenor St, University of Manchester, Manchester M13 9PL, UK and The Research Complex at Harwell, Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0FA, UK philip.withers@manchester.ac.uk P. Lopez-Crespo Department of Civil and Materials Engineering, University of Malaga, C/ Doctor Ortiz Ramos, s/n, 29071, Malaga, Spain plopezcrespo@uma.es M. Mostafavi Department of Mechanical Engineering, University of Sheffield, Sir Frederick Mappin Building, Mappin Street, Sheffield S1 3JD, UK m.mostafavi@sheffield.ac.uk A. Steuwer Nelson Mandela Metropolitan University, Gardham Av., 6031 Port Elizabeth, South Africa axel.steuwer@gmail.com J. F. Kelleher ISIS, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX, UK joe.kelleher@stfc.ac.uk T. Buslaps ESRF, 6 rue J Horowitz, 38000, Grenoble, France buslaps@esrf.fr A BSTRACT . The evolution of crack-tip strain fields in a thin (plane stress) compact tension sample following an overload (OL) event has been studied using two different experimental techniques. Surface behaviour has been characterised by Digital Image Correlation (DIC), while the bulk behaviour has been characterised by means of synchrotron X-ray diffraction (XRD). The combination of both surface and bulk information allowed us to visualise the through-thickness evolution of the strain fields before the OL event, during the overload event, just after OL and at various stages after it. Unlike previous work, complete 2D maps of strains around the crack-tip were acquired at 60  m spatial resolution by XRD. The DIC shows less crack opening after overload and the XRD a lower crack-tip peak stress after OL until the crack has grown past the compressive crack-tip residual stress introduced by the overload after which the behaviour returned to that for the baseline fatigue response. While the peak crack-tip stress is supressed by the compressive residual stress, the crack-tip stress field changes over each cycle are nevertheless the same for all K max cycles except at OL.