Experiment And Simulation Methods To Investigate Mechanics Behavior Of New Structure Materials

Low-cycle-fatigue (LCF) and fatigue-crack-propagation (FCP) properties of materials play great roles in the life assessment of structures. For nuclear power structural materials: Zr-Sn-Nb, TA17 and Cr2Ni2MoV steel, their LCF and FCP behavior were systematically investigated by tests and numerical simulations. The main works are given as follows:(1) As for small curvature radius funnel-like notched specimens, a test method of LCF tests by local fatigue damage equivalent (LFDE) and finite element analysis (FEA), named as LLF method, was presented on the basis of fatigue damage equivalent assumption. For LLF method, the uniaxial strain extensometer fixed on the side of a funnel-like specimen is used to control LCF tests, and the strain conversion model from the uniaxial strain to the local equivalent strain at the notch root of the specimen is established by FEA, and then Manson-Coffin life estimation model can be obtained.(2) A series of monotonic tension tests of Zr-Sn-Nb alloy were carried out at several temperatures from 20℃to 500℃, and corresponding uniaxial constitutive models were given. Based on LLF method, LCF tests of Zr-Sn-Nb alloy were conducted using funnel-like slice-specimens at the elevated temperatures, consequently, Manson-Conffin models for LCF life prediction at the temperatures were presented.(3) The elevated temperature effect on both cyclic strength and static strength of Zr-Sn-Nb alloy decreases greatly at the start, and then decreases stationary gradually, moreover, the influence of elevated temperature on cyclic strength is greater than that on static strength. Fatigue life of Zr-Sn-Nb alloy decreases with increase of temperature, and the life varies linearly with uniaxial strain amplitude. Furthmore,λ-Manson-Coffin model for LCF life prediction of Zr-Sn-Nb alloy was established.(4) Test investigations on fatigue and fracture behavior of TA17 alloy and Cr2Ni2MoV steel were performed, and their fatigue properties obtained are useful for nuclear power engineering.(5) A new numerical simulation method by using LCF tests and FEA to predict FCP rate of materials and structures, named as LFF method, was presented. For LFF method, it is assumed that the critical fatigue damage within plastic region ahead of crack tip is the same as critical LCF damage of an uniaxial smooth specimen, and then an average fatigue damage parameter is defined according to Manson-Coffin model, as well as the direction perpendicular to maximum principal strain direction is defined as FCP direction. ANSYS command stream was developed to realize LFF numerical simulation algorithm, and secondary development of ANSYS software was carried out to implement sequencing calculation of FCP rate. For compact tensile (CT) specimens with complicated crack for Cr2Ni2MoV steel and straight crack for TA12 alloy and TC4 alloy, LFF method was applied to predict their FCP behavior. The results show that LFF method has better predicted accuracy for many kinds of materials.Based on the test and FEM analysis, yield stress and buckling strength of steel-plastic composite pipes with different dimension were given and temperature and dimension effects on yield and buckling strength of steel-plastic composite pipes were investigated. A new model to estimate the yield strength and buckling strength of steel-plastic composite pipes with out-diameter from 50mm to 400mm was presented and it has enough precision.