A Study On The Multiaxial Ratcheting Behavior Of Zirconium Alloy At High Temperature

In this paper,a series of tests have been conducted on zirc onium alloy at elevated temperature of 350?which is used as nuclear fuel cladding in nuclear reactors The influence of multiaxial loading on the behavior of zirconium alloy's ratcheting was studied.The effect of stress amplitude,mean stress,loading history and loading path on the multiaxial ratcheting was studied by uniaxial tension and uniaxial/multiaxial ratcheting tests.The fracture and surface of the fracture failure samples were observed by scanning electron microscopy(SEM and EBSD).The fatigue fracture morphology and micro-deforming mechanism of the alloy at 350?were analyzed.Furthermore,Chaboche model,OW-II model and C-J-K model were used to simulate the uniaxial/multiaxial ratcheting effect of zirconium alloy thin-walled tube by finite element software ANSYS.The conclusions can be drawn as follows:(1)The yield strength ?_s and the tensile strength ?_b of zirconium alloy at 350?are significantly decreased,and its ductilityat 350°C is poorer than that at RT.(2)The ratcheting behavior of zirconium alloy at 350°C depends greatly on the mean stress and stress amplitude,the ratcheting strain greatly increases when the mean stress or stress amplitude increase s.(3)The uniaxial fracture strain of zirconium alloy at 350°C is significantly increased due to the presence of hoop stress.(4)Zirconium alloy presents a strong memory of the loading history.A lower stress amplitude after a loading history with a higher stress level greatly constrains the accumulation of ratcheting strain.(5)The tensile holding period significantly affects the ratcheting behavior of zirconium alloy at 350°C,indicating that zirconium alloy is a time-dependent material.The longer the tensile holding time,the larger the creep strain.(6)Through fracture analysis of the specime n by SEM,the failure of the material belongs to ductile fracture.(7)The surface of the failed specimen was observed by EBSD,and the grain orientation was almost unchanged before and after the test.(8)Compared with the Chaboche model and the Ohno-Wang II model,the C-J-K model is the most ideal for the multiaxial ratcheting effect through the introduction of multiaxial coefficient.