A Study On Multiaxial Ratcheting Behavior Of Zr-Sn-Nb Alloys Under The Combined Of Axial Load And Internal Pressure

Zirconium alloys are widely used in nuclear reactors due to their high mechanical strength,strong corrosion and creep resistance,and low thermal neutron absorption cross-sections.In this paper,Zr-Sn-Nb alloy is used as the research object.A series of uniaxial and multiaxials ratcheting tests are carried out under internal pressure and axial stress loading at room temperature and 375 °C.The multiaxial ratcheting behavior of Zr-Sn-Nb alloy and Zr-Sn-Nb are compared at room temperature.The effects of temperature,axial stress amplitude,internal pressure and the element of alloy on the uniaxial/multiaxial ratcheting behavior of zirconium alloy are investigated.The main conclusions are as follows:(1)At room temperature,under the internal pressure and axial stress loading,the increase of axial stress amplitudes increase the axial ratcheting strain and the hoop ratcheting strain for Zr-Sn-Nb alloy;the internal pressures inhibit the accumulation of axial ratchet strain and promote the accumulation of hoop ratcheting strain.(2)Under the same multiaxial load condition,the effect of internal pressure on the hoop ratcheting strain of Zr-Nb alloy is more significant than that of Zr-Sn-Nb alloy.The stress amplitude also has more significant effect on the axial ratchet strain accumulation of Zr-Nb alloy than that of Zr-Sn-Nb alloy,which indicate the appropriate amount of Sn element can enhance the ability of the Zr-Sn-Nb alloy to resist ratcheting deformation.(3)At 375 °C,the elastic modulus,yield strength,tensile strength and elongation of Zr-Sn-Nb alloy are significantly lower than that at room temperature.(4)At 375°C,under the uniaxial symmetrical cyclic loading,the axial ratcheting accumulates in compression direction due to the change of the deformation mechanism at high temperature for Zr-Sn-Nb alloy,as the mean stress increases,the axial ratcheting accumulates in tensile direction.(5)At 375°C,The multiaxial ratcheting behaviors of Zr-Sn-Nb alloy are more sensitive to axial stress amplitude and internal pressure when internal pressure and axial stress loading are applied simultaneously.hoop ratcheting strain and axial ratcheting strain increase with the increase of axial stress amplitude;the increase of internal pressure inhibit the accumulation of axial ratcheting strain largely and promote the hoop ratcheting strain greatly.(6)At 375°C,Zr-Sn-Nb alloy shows significant time dependence,and the axial ratcheting strain increases rapidly with the increase of axial peak holding time.During the progress of cycles,the creep strain accounts for the main part of the axial ratcheting strain.