Fatigue Behavior And Mechanism Of Ti-6Al-4V Alloy Under Complex Temperature Field

Since the 1960s,the world has made significant scientific and technological achievements in the field of launching and returning intercontinental ballistic missiles and manned space shuttles.With the development of science and technology,human beings have entered a new field of supersonic vehicle.The flight trajectory of a hypersonic vehicle is a"boost glide"trajectory,in which the aircraft will repeatedly enter and exit the atmosphere.In the reentry stage,the friction between the aircraft and the atmosphere will produce a higher temperature.After the aircraft flies out of the atmosphere,it enters the outer atmosphere with a relatively lower temperature.The periodically varying temperature field will make the shell of aircraft components bear periodically varying thermal stress,which will eventually lead to thermal stress fatigue of components.At the same time,long-term exposure to the surface of aircraft at higher temperatures is prone to oxidation reaction in unprotected or damaged areas,resulting in oxide layer,which will also lead to premature damage of components.In view of the appeal problem,the fatigue behavior and mechanism of Ti-6Al-4V alloy under complex temperature field were studied by combining cyclic oxidation experiment and Abaqus/FE-SAFE coupled simulation method,aiming at Ti-6A1-4V(TC4)titanium alloy widely used in aerospace industry.The cyclic oxidation tests of Ti-6Al-4V alloy at 550,600,650,700 and 750?C were carried out in crucible resistance furnace.The micro-morphology of the samples after cyclic oxidation was observed by scanning electron microscopy(SEM)of HYKY-EM3200.The hardness of the samples from core to surface was measured by HDX-1000TMB digital microhardness tester,and the surface shape of the oxide layer generated by aircraft under complex temperature field was explored.Appearance and characteristics.Quasi-static tensile tests were carried out on INSTRON 5980 double-column ground-mounted tester.The mechanical properties of samples with oxide layer removed and containing after oxidation at these three temperatures were tested.The effects of-oxide layer on the mechanical properties and deformation behavior of Ti-6A1-4V rod specimens were investigated.Based on the finite element analysis software ABAQUS and the fatigue prediction software FE-SAFE,the fatigue life of Ti-6Al-4V Titanium Alloy Rod Specimens under the influence of uniform temperature field with periodic change was analyzed by coupling the oxide layer and background stress with periodic change.The effect of thermal stress on the fatigue properties of Ti-6A1-4V titanium alloy under the influence of complex temperature field with periodic change was studied.Based on the finite element analysis software ABAQUS and fatigue prediction software FE-SAFE,the fatigue model of the conceived aircraft components was established and analyzed.The effects of periodically varying non-uniform temperature field and uniform temperature field on the fatigue behavior of the aircraft components were studied.