Comparison of crack paths in a forged and extruded aeronautical titanium alloy loaded in torsion in the gigacycle fatigue regime
TypeArticles dans des revues avec comité de lecture
This paper discusses features of fatigue crack initiation and growth in an extruded and forged VT3-1 titanium alloy loaded in pure torsion in the gigacycle regime. Torsion fatigue tests were performed at 20 kHz up to a fatigue life of 109 cycles. It has been shown that regardless of the manufacturing process both surface and subsurface crack initiation may appear under ultrasonic torsion loads despite the fact that the maximum shear stress amplitude is located at the specimen surface. In the two cases cracks initiate on planes of maximum shear stress amplitude (mode II). After reaching a certain length the cracks turn and propagate in mode I. Surface crack initiation and growth mechanisms in VHCF regime are similar to HCF ones. Subsurface crack forms a typical ‘‘fish-eye” pattern on fracture surface with three different zones: (1) small crack growth in the plane of maximum shear stress, (2) crack growth on the plane of maximum normal stress with the formation of a quasi-flat failure surface covered by fretting debris, (3) crack branching under mixed mode loading conditions (I + II + III) with the formation of several secondary cracks. Subsurface crack initiation sites are located below the specimen surface (at a depth of approximately 200 lm) for both the forged and the extruded materials. Subsurface crack growth is observed on the failure surface as being less rough. The mechanisms of subsurface crack initiation seems to be similar to these observed under fully reversed tensile loads.
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NIKITIN, Alexander; BATHIAS, Claude; PALIN-LUC, Thierry; SHANYAVSKIY, Andrey (Gruppo Italiano Frattura, 2015)This paper discusses features of fatigue crack initiation and growth in aeronautical VT3-1 titanium alloy under pure torsion loading in gigacycle regime. Two materials: extruded and forged VT3-1 titanium alloys were studied. ...
NIKITIN, Alexander; PALIN-LUC, Thierry; SHANYAVSKIY, Andrey (Elsevier, 2016)This paper is focused on the VHCF behavior of aeronautical titanium alloy under tensile and torsion fatigue loadings. Tensile tests were carried out with two different stress ratios: R = À1 and R = 0.1. Both surface and ...
NIKITIN, Alexander; SHANYAVSKIY, Andrey; PALIN-LUC, Thierry (DVM, 2017)This paper is focused on fatigue crack initiation and early growth in two-phase titanium alloy VT3-1 (similar to Ti-6Al-4V) under VHCF loads. The material was produced by two different processes: forging and extrusion. ...
Fatigue crack initiation and growth on an extruded titanium alloy in gigacycle regime: comparison between tension and torsion loadings NIKITIN, Alexander; PALIN-LUC, Thierry; SHANYAVSKIY, Andrey (Elsevier, 2016)This paper is focused on the analysis of fatigue crack initiation and growth mechanisms in defect free VT3-1 titanium alloy (similar to Ti6Al4V) in VHCF regime under tensile and torsion loadings. Fully reversed fatigue ...
A new piezoelectric fatigue testing machine in pure torsion for ultrasonic gigacycle fatigue tests: application to forged and extruded titanium alloys NIKITIN, Alexander; BATHIAS, Claude; PALIN-LUC, Thierry (Wiley, 2015)This article briefly discusses the history of the development of ultrasonic fatigue testing methods, with respect to industrial needs. The development of ultrasonic techniques and the progress made in the computer industry ...