Issue 37

F. Berto et alii, Frattura ed Integrità Strutturale, 37 (2017) 69-79; DOI: 10.3221/IGF-ESIS.37.10 69 Focussed on Multiaxial Fatigue and Fracture Local strain energy density to assess the multiaxial fatigue strength of titanium alloys Filippo Berto University of Padova, Department of Management and Engineering, Vicenza (Italy) NTNU, Department of Engineering Design and Materials, Trondheim, (Norway) berto@gest.unipd.it Alberto Campagnolo University of Padova, Department of Industrial Engineering, Padova (Italy) alberto.campagnolo@unipd.it Torgeir Welo NTNU, Department of Engineering Design and Materials, Trondheim, (Norway) torgeir.welo@ntnu.no A BSTRACT . The present paper investigates the multiaxial fatigue strength of sharp V-notched components made of titanium grade 5 alloy (Ti-6Al-4V). Axisymmetric notched specimens have been tested under combined tension and torsion fatigue loadings, both proportional and non-proportional, taking into account different nominal load ratios (R = -1 and 0). All tested samples have a notch root radius about equal to 0.1 mm, a notch depth of 6 mm and an opening angle of 90 degrees. The fatigue results obtained by applying multiaxial loadings are discussed together with those related to pure tension and pure torsion experimental fatigue tests, carried out on both smooth and notched specimens at load ratios R ranging between -3 and 0.5. Altogether , more than 250 fatigue results (19 S-N curves) are examined, first on the basis of nominal stress amplitudes referred to the net area and secondly by means of the strain energy density averaged over a control volume embracing the V-notch tip. The effect of the loading mode on the control volume size has been analysed, highlighting a wide difference in the notch sensitivity of the considered material under tension and torsion loadings. Accordingly, the control radius of the considered titanium alloy (Ti-6Al-4V) is found to be strongly affected by the loading mode. K EYWORDS . Ti-6Al-4V; Multiaxial fatigue; V-notch; Control volume; Strain Energy Density. I NTRODUCTION or a wide comparison between different approaches adopted to the multiaxial fatigue strength assessment of metallic materials, the reader is referred to a recent review [1] and a report [2], which are based on a large bulk of experimental data obtained from notched specimens. A fundamental role is occupied by critical plane approaches F