Issue 37

M. Mokhtarishirazbad et alii, Frattura ed Integrità Strutturale, 37 (2016) 114-123; DOI: 10.3221/IGF-ESIS37.16 114 Focussed on Multiaxial Fatigue and Fracture Experimental and analytical study of cracks under biaxial fatigue M. Mokhtarishirazbad, P. Lopez-Crespo, B. Moreno, D. Camas Department of Civil and Materials Engineering, University of Malaga, C/Dr Ortiz Ramos s/n, 29071, Malaga, Spain plopezcrespo@uma.es A. Lopez-Moreno Department of Materials Science and Metallurgy Engineering, University of Jaen, Campus Las Lagunillas, 23071, Jaen, Spain alopez@ujaen.es M. Zanganeh ORAU, Oak Ridge, TN, USA mohammad.zanganehgheshlaghi@nasa.gov A BSTRACT . Most mechanical components experience multi-axial cyclic loading conditions during service. Experimental analysis of fatigue cracks under such conditions is not easy and most works tend to focus more on the simpler but less realistic case of uni-axial loading. Consequently, there are many uncertainties related to the load sequence effect that are now well known and are not normally incorporated into the growth models. The current work presents a new methodology for evaluating overload effect in biaxial fatigue cracks. The methodology includes evaluation of mixed-mode (K I and K II ) stress intensity factor and the Crack Opening Displacement for samples with and without overload cycle under biaxial loading. The methodology is tested under a range of crack lengths. All crack-tip information is obtained with a hybrid methodology that combines experimental full-field digital image correlation data and Williams' elastic model describing the crack-tip field. K EYWORDS . Stress intensity factor; Biaxial fatigue; Mixed-mode; Crack opening displacement. I NTRODUCTION eliable life-time prediction of structural materials subjected to external loadings depends strongly on the accuracy of the fracture parameters estimation. So far, a number of successful approaches have been presented for estimating the essential fracture parameters such as stress intensity factors (SIFs) experimentally [1]. Apart from the conventional standard test methods [2], it has been shown that crack-tip fields (strain, stress and displacement field) include essential information for accurate estimation of fracture parameters [3]. A number of different techniques are able to provide both surface and bulk information. Surface techniques include photo-elasticity [4], thermo-elasticity [5], Moiré interferometry [6] and digital image correlation (DIC) [7]. Bulk techniques include neutron diffraction [8] and X-ray diffraction [9]. Among all these full-field techniques, DIC has received enormous attention recently [10,11] because of its many advantages compared to other techniques [12]. Simplicity, accuracy and flexibility are the most prominent merits of R