Research On Fatigue Design Method Of High-heat-load Components Of SSRF Based On Study Of Fatigue Properties Of Copper Materials

As a third-generation of synchrotron radiation facility,Shanghai Synchrotron Ra-diation Facility(SSRF)provides light source with extremely high radiation power den-sity.The high heat load components in the front end,which is between the storage ring and the beam line,are key components which is employed to absorb the most of the heat generated by the beam line incidence and to supply thermal protection for other components.The high heat load brings great challenges to the design of the high heat load components.As the key components are designed to serve for 30 years,equiv-alent to 10,000 thermal cycles,the design method based on static strength theory for heat load components in SSRF is too conservative and not so economic.The proposal of a reasonable and effective design method is required by the further development of synchrotron radiation facility.Based on the project of National Natural Science Foundation of China,"study on the fatigue failure of Glidcop under high heat load of synchrotron radiation",this disser-tation aims at the proposal of a new design method of the high heat load components at the front end of synchrotron radiation facility.It focuses on low cycle fatigue properties of Glidcop,effect of various treatments on fatigue life and the fatigue life predictions for experimental specimens as well as the high heat load component of SSRF.The numeri-cal simulation,experimental observation and crack propagation modeling are conducted systematically.The fatigue life design method based on the damage tolerance theory is suggested to provide a significant direction for the optimal design of the high heat load components.The main contents of this dissertation are as follows.(1)Study on the low-cycle crack propagation properties of GlidcopGlidcop is used for manufacture of the front end components of SSRF.The fatigue crack propagation properties of the material are required for damage tolerance design.Experiments have been conducted on Glidcop specimens under a range of cycle loadings by MTS.Crack propagation process has been investigated and the relationship of fatigue crack growth rate and the loading level as well as the crack length is revealed as the Tomkins expression.The quantitative equation of crack growth rate will be used for low-cycle fatigue prediction of this material.(2)Effect of annealing and surface roughness on the fatigue properties of pure copperIt has been revealed that mechanical properties of copper and copper alloys are related to heat treatment.In this dissertation,the effects of annealing treatment and the surface roughness to the fatigue properties of pure copper were studied.It can be found that the tensile strength and the fatigue properties changed significantly after annealing.It is suggested not to anneal pure copper or Glidcop(Cu 99.7%)when the material strength is required in service.(3)Effect of pulsed electric treatment on the fatigue lifeElectric pulsing treatment(EPT)has been proved to have positive effect on fatigue properties by healing fatigue crack in metallic materials.As rough surface can be regard as a series of small notches and cracks,the effect of EPT on the fatigue life of rough specimens is studied here.Observations for surface topography,metallographic struc-ture,surface residual stress and fracture surface configuration have been conducted for pure copper specimens.The effect of EPT on fatigue life of pure copper and Glidcop is discussed.Notched specimens were used for investigation of effect on crack propaga-tion by EPT.It was found that the fatigue lives of cold-worked pure copper and Glidcop increase after EPT.The fatigue life of heat load component with small roughness can be prolonged by using proper EPT,which will benefit the operation of the whole facility.(4)Crack propagation life prediction for specimens with defectsRough surface can be regenerated by statistical parameters from measurement of real surface,thus the stress and strain distribution can be obtained by the finite element analysis from the regenerated model.Stress intensity factor and local plastic strain range are chosen to be the effective parameters for high-cycle and low-cycle fatigue crack propagation,respectively.The two controlling parameters of specimens with defects,such as notch or rough surface,were calculated by FEA.Based on the assessment of crit-ical crack length and the crack propagation rate,the crack propagation lives of notched copper specimen,holed and rough Glidcop specimen were effectively predicted.The method is proved to be reasonable and effective by the fine agreement between predicted lives and the experimental data(5)Crack propagation life prediction and finite fatigue life design method for the high heat load components of SSRFThe results of cyclic stress and strain by elastoplastic FEA for a high heat load component are used for fatigue life prediction.Based on the damage tolerance the-ory,the local plastic strain range is chosen as the controlling parameter and the critical crack length to failure is set as 1 mm.The low-cycle crack propagation rate is intro-duced to predict fatigue life for beam in normal working case or in completely drift case,respectively.Final estimated fatigue life can be obtained by using the linear cumula-tive damage theory which combines the normal and drift cases.In conclusion,the finite fatigue life design method based on damage tolerance theory for the high heat load com-ponents is proposed,which brings out a innovative way for the design and optimizing of the components in the future.