Issue 41

J.V. Sahadi et alii, Frattura ed Integrità Strutturale, 41 (2017) 106-113; DOI: 10.3221/IGF-ESIS.41.15 106 Focused on Multiaxial Fatigue Prediction of fatigue crack initiation under biaxial loading J.V. Sahadi, D. Nowell, R.J.H. Paynter University of University of Oxford, Department of Engineering Science, Parks Road, Oxford, OX1 3PJ, UK. joao.sahadicavalheiro@eng.ox.ac.uk , david.nowell@eng.ox.ac.uk , robert.paynter@eng.ox.ac.uk A BSTRACT . This investigation revisits biaxial fatigue experiments carried out with the nickel-based superalloy termed Waspaloy. Recently, yield criteria extended to multiaxial fatigue and stress based approaches were analysed and their performance to correlate the biaxial test data was evaluated. It was concluded that despite their reliable results, the parameters did not properly represent the physical behaviour of the material. In this context, an extension of this study was executed considering the strain based critical plane approaches proposed by Fatemi-Socie (FS) and Smith- Watson-Topper (SWT). The first parameter presented overly conservative predictions with large scatter of results. In contrast, more accurate predictions were obtained with the SWT parameter. K EYWORDS . Biaxial fatigue; Fatigue Life; Waspaloy; Critical Plane Approach. Citation: Sahadi, J.V., Nowell, D., Paynter, R.J.H., Prediction of fatigue crack initiation under biaxial loading, Frattura ed Integrità Strutturale, 41 (2017) 106-113. Received: 28.02.2017 Accepted: 15.04.2017 Published: 01.07.2017 Copyright: © 2017 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION dvances in material testing equipment and techniques during the past 40 years enabled the development of more realistic multiaxial fatigue tests by applying loads representative of service life, at different temperature settings (room, low or elevated temperatures), test frequencies and load phase shift. Among the most used techniques, cruciform specimens and thin-walled tubular specimens have been broadly used for fatigue testing under biaxial stress states [1]. Yet tension-torsion specimens pose limitations when it comes to probing the entire principal stress plane,  1 vs  2 , and only 2 of its 4 quadrants can be investigated. Nevertheless, with different techniques, such as internally pressurized tubular specimens, it is possible to access more of the principal stress plane. The combination of cruciform specimens and axial-torsional specimens, internally pressurized, allow the investigation of almost the entire principal stress plane. However, for cruciform specimens the assessment of biaxial compression region is commonly challenging due to testing machine limitations. In the literature, examples of fatigue life investigation using tubular specimens are available in [2–4]. Cruciform specimens and biaxial test rigs allow the investigation of a broad range of biaxiality. However, specimens are expensive and testing is complex. Work on biaxial testing with cruciform specimens can be found in [5–7]. Recent work at Oxford on biaxial fatigue testing and total life prediction using multiaxial fatigue criteria has been presented at the Eleventh International Conference on Multiaxial Fatigue and Fracture and published on the special issue of the conference [8]. The present paper presents further developments on the investigation of multiaxial fatigue criteria and their predictions for the biaxial test results presented at [8] A