Modeling And Exprimental Device Development Of T-pipe Thermal Fatigue Crack

Metal pipes with small cracks(or hidden cracks)are widely used in industrial heat exchange process.They can be used normally in most cases,but if they continue to develop into penetrating fractures during service,they will cause serious safety accidents.The crack propagation caused by thermal fatigue is mostly the result of long-term evolution under the synergistic action of multiple factors,such as heat,flow and solid.In recent years,it has become an important way to further explore this problem by comprehensively analyzing the various factors of heat,flow and solid based on the theoretical model,combined with numerical modeling and simulation technology and experimental research.Therefore,in this paper,the thermal fatigue crack propagation model of Tpipe considering the mechanical properties of pipes is studied,and the experimental device of thermal fatigue crack propagation is trial-produced with the theoretical support of numerical model,which has important theoretical value and practical significance for promoting the relevant mechanism research and the development of monitoring technology.Based on the analysis of the thermal fatigue process of metal pipe and the theoretical models of fluid,heat transfer and stress,and considering the factors of thermal stress field,energy field and pipe structure,the method to determine the initial initiation zone of pipe crack and the relevant stress data is presented.As a key research area,considering the pipe mechanical properties,in view of the existing model of the pipe/crack tip not fully considered a singularity problem,introducing the extended finite element method,the enhancement function is used to describe the singularity of the cracked in the micro level,set up the T pipe thermal fatigue crack extension theory model,gives the algorithm process,the theoretical solution.Based on the theoretical models of the above parameters,an experimental device for thermal fatigue crack propagation was developed,and the thermal fatigue data obtained by the experimental device were in good agreement with the theoretical solution.Based on Ansys Fluent software to build the T tube first physical model and internal flow field model,set up four kinds of typical working condition and boundary conditions,the pipe under the action of a hot-flow-solid mixed state,such as temperature,thermal stress,energy distribution,and the results show that the field distribution,maximum stress field,energy field in the fluid fusion downstream area,this is the hidden crack initial initiation area.Secondly,according to the thermal stress data in the initial initiation zone of crack,the numerical simulation of crack propagation of T-shaped pipe based on the extended finite element method was carried out by ABAQUS software.The initial crack length was set as 150?m in the initial crack initiation zone,and the crack type was set as XFEM to characterize the singular field of crack/crack tip surface.The Poisson's ratio was set as 0.3 and the elastic modulus was set as 212 to characterize the mechanical properties of Q235 stainless steel pipe.Finally,develop these hidden fatigue crack extension experiment device,specimen,the choice of heating temperature and cooling temperature on the simulation research for reference,electromagnetic induction heating system and real-time monitor system as the main experiment device components,setting device heating-cooling circulation way,get Q235 metal pipe under the experimental conditions of thermal fatigue performance data.The results show that under the four working conditions of the thermal fatigue crack expansion experimental device,the pipe cracking phenomenon gradually becomes earlier with the increase of heating temperature.For example,when the crack length expands from 200?m to500?m,the thermal stress load cycles are 2200 times at 400-20?,and about 6000 times at 250-20?.In other words,the crack growth rate at 400-20? is 2.73 times as fast as that at 250-20?.In the numerical simulation,the crack growth rate at 400-20? is 2.79 times that at 250-20?.The experimental results are in good agreement with the numerical simulation results,which verifies the effectiveness of the numerical model and the thermal fatigue crack experimental device,and has a guiding significance for promoting theoretical research and equipment development.