Fastening Force Study Of Shape Memory Alloy Pipe Connection

The shape memory alloy(SMA)has the outstanding shape memory effect,superelasticity,corrosion resistance,high damping,high resistive and so on,widely applying in engineering.In the application,the pipeline joint based on shape memory effect(SME)is the most representative use.The SMA pipe joint initial diameter is usually less than the outer diameter of the connected pipes at room temperature,and it is easy to install two steel pipe in the pipe joint after expanding to make the pipe joint diameter greater than the connected pipe outer diameter.After high temperature heating and cooling,the pipe joint can memory its small diameter in original and its diameter is gradually narrowed because of the martensitic transformation,eventually pipe joint and steel pipe produce interference fit,and hugging,fix and connect two steel pipe.Therefore,the SMA-based pipe connection technique has wide application prospect.The research focus of this dissertation is how to design and improve the existing SMA pipe joint to meet the requirement of its radial stress in pipe connection.So we can use a simplified constitutive model for SMA can indeed fit the SMA pipe coupling structure.Meanwhile,in the design of the SMA connection,the design method and technical parameters are also very important.The combination method of theoretical analysis,numerical simulation and experimental validation is used to investigate the fastening force in the SMA pipe connection,aiming at proposing a large dimension iron-based SMA pipe connection design method,and validating its efficiency through experiments.The main contents include as following:(1)Improving SMA material constitutive model and analyzing the mechanism of pipe connection.Based on Boyd and Lagoudas model,Misses yield surface equation in plastic mechanics is used to simplify the model.A new multi-dimensional SMA constitutive model is improved with a simpler expression for the model.(2)SMA pipe connection mechanical performance analysis.Matlab and ABAQUS are used to develop the SMA pipe connection mechanical performance,researching on the impact law of connected pipe dimensions and training issue of the pipe connection on fastening forces.(3)SMA pipe connection experimental research.A new iron-based SMA connection element is redesigned.The feasibility of the new developed SMA pipe connection is validated by experiment.Through the pipe connection experiment at elevated temperatures,the connecting process of the iron-based SMA pipe connection and connected pipes is observed.Through the compare of the elevated temperature connection experiment and free recovery one,the radial stress of the pipe connection is evaluated by the connected pipe deformation calculation.(4)Compare of the experimental results and numerical ones.Through the calculation,the failure mode of the experimental results is reasonably evaluated.Through the pull-out test,the relationship among pull out force,stress and time is obtained,t further validating the failure mode of the pipe connection.Through the compare of numerical simulation and experimental data,the accuracy and feasibility of numerical experiment is also further validated.Theoretical analysis,numerical simulation and experimental validation all prove that the proposed iron-based SMA pipe connection can produce the required fastening forces which can meet the requirement of pipe connection.