Research On Electrohydraulic Expansion Joints For Aluminum Alloy/Stainless Steel Pipes For Pipeline Connection

In recent years,aviation accidents have occurred frequently,and aviation safety has attracted special attention.Aviation pipeline system is prone to mechanical failures.The sealing failure of pipe system is mostly caused by the failure of connecting joints.The flare-free joint is an advanced connection structure.However,key technologies such as structural design and joining process are subject to European and American restrictions.In addition,aluminum alloy pipes and stainless steel pipes are most commonly used in the aviation industry,but aluminum alloys have poor formability at room temperature.Aluminum alloy is easy to crack during quasi-static forming at room temperature.The joining between aluminum alloy pipe and stainless steel pipe is facing challenges.In order to solve the joining problem between aluminum alloy pipe and stainless steel pipe.AA6063 aluminum alloy and 304 stainless steel were selected.Electrohydraulic expansion joining process was used.Firstly,the test platform for pipe electrohydraulic forming and joining was built.The electrohydraulic joining process was carried out.The joint performance was evaluated.Secondly,numerical simulation was used to analyze the joining process.Then,the deformation response analysis and prediction model of the inner pipe was built in the electrohydraulic expansion joining process.Finally,the joint strength prediction model was established.The main research contents of this paper were as follows:(1)During the electrohydraulic free forming process,the pipe deformation behavior measurement system was built.The coaxial electrode system was proposed.The laws of the displacement,velocity,strain and strain rate of the material changing with time during the electrohydraulic free forming process were obtained.Research showed that the new electrode system was easy to assemble.It required little space.When the discharge voltage was 3.5 k V,the maximum speed reached 44157.5 mm/s.The velocity distribution of the inner pipe was more uniform on the y-axis.(2)The coaxial electrode system was used to carry out the electrohydraulic expansion joining process was carried out.The influence of different process parameters on joint performance was explored.The electrohydraulic expansion joint of aluminum alloy pipes and stainless steel pipes was obtained under different discharge voltages.The yield load and tensile load were used to evaluate the performance of electrohydraulic expansion joints.The failure mode and energy absorption capacity of the electrohydraulic expansion joint in pull-out test were studied.The results showed that when the discharge voltage increased by 12.5%,the yield load increased by 27.87%,and the tensile load increased by 12.97%.There were two failure modes of joints.Different failure modes have different energy absorption capacities.(3)The numerical simulation model for the electrohydraulic expansion joining of aluminum alloy/stainless steel pipe dissimilar materials was established.The groove filling ratio was introduced to characterize the deformation results.Geometric factors affecting joint performance were analyzed.The angleα_i and length L_iwere defined.In a certain range,when theα_i decreases and the L_i increases,the deformation of the inner pipe increases.The groove is filled with more materials.The tensile load is increased(4)The radial displacement prediction model of the central position of the cylindrical shell under different loads was established.Firstly,the criteria for high load and low load were defined.Plastic failure mechanisms corresponding to different impact loads were obtained.The radial displacement expression was obtained by plastic dynamic analysis.A method of pulse load conversion was introduced to convert non rectangular pulse into rectangular pulse for solution.The test platform for the electric explosion pressure of metal wires in water was built.The electric explosion pressure model of metal wires in water was built.Then,according to the pressure time history and the radial displacement prediction model,the radial displacement prediction of the center of the inner pipe was realized.(5)The strength prediction model of electrohydraulic expansion joint was established.Firstly,the stress state of the inner pipe of the electrohydraulic expansion joint was analyzed.The stress change caused by the change of curvature radius was discussed.The effect of friction on axial force was discussed.Then,based on the membrane theory,the prediction analysis model of the yield load of the electrohydraulic expansion joint was established.The response functions of tensile load and groove width,discharge voltage,wire length and wire diameter were established through central composite design and relevant experiments.The quaternion second order polynomial regression analysis model of tensile load was obtained.