Numerical Simulation Of Ductile Fracture And Strength-Ductility Of Hydrogenated Zirconium Alloys

As the first safety barrier of nuclear reactor,zirconium alloy cladding tube has attracted extensive attention because of its good mechanical properties.The zirconium alloy is a key material so the evaluation of its ductile fracture process and strengthductility is of great significance to prolong its service life.In this dissertation,the influences of hydrides on the ductile fracture process together with the strength and ductility of zirconium alloys have been numerically studied.First,based on a triaxiality dependent cohesive zone model,a compact tension analysis configuration is established for hydrogenated zirconium alloys composed of matrix and hydrides under the condition of plane strain.By comparing with the prediction results based on extended finite element method,the model parameters are estimated and the validity of the model is verified.The results show that the presence of hydrides accelerates the crack propagation and decreases the post-peak load level after the peak load.Moreover,the fracture resistance of zirconium alloys is strongly affected by the length,arrangement,quantity,and spacing of the hydrides.Specifically,when the major axis of hydride is along the crack propagation path,the peak load increases and the corresponding boundary displacement decreases with the increase in the hydride length.The increase in their quantity reduces the post-peak load level.Besides,the increase in their spacing enhances the boundary displacement corresponding to the sudden load drop.Secondly,based on the bilinear traction-separation law,the effects of cohesive strength,interface fracture characteristics,and hydride geometry characteristics on the strength and ductility are numerically simulated in a two-dimensional situation.The results show that the fracture characteristics of the two-phase materials and the initiation sites of cracks in the hydride are affected by the cohesive strength,and that the strength and ductility are sensitive to the variation of the cohesive strength of the zirconium matrix.The interface has significant effects on the fracture behavior of the entire materials.When the cohesive strength and fracture energy of the interface are higher than those of the hydride phase,the hydride fracture occurs first,which is consistent with the experimental phenomenon.In addition,the geometric characteristics of hydrides have obvious effects on the strength and ductility of materials.Specifically,the change of hydride length has slight effects on the strength and ductility of materials.Under the same volume fraction,the more hydrides with the major axis along the tensile direction while not in the same line,the worse the overall strength and ductility.The mechanical properties of the materials with the hydrides along the tensile direction are much better than those with other configurations.The results of this dissertation provide insights into the effects of hydrides on the ductile fracture process of zirconium alloy,and serve as theoretical and technical support for the mechanism analysis of hydrogen embrittlement of zirconium alloy during the operation of nuclear reactor.