Research On The Wrinkling Behavior Of Thin-walled Pipes Under Axial Compression Under Non-uniform Temperature Field

Tube hydroforming technology is an advanced technology for manufacturing lightweight hollow thin-walled components.The method of using beneficial wrinkles to accumulate materials in the deformation zone further achieves the forming of aluminum and magnesium alloy tube fittings with a large expansion rate.However,the beneficial wrinkles prefabricated by the hydroforming technology are restricted by the mold cavity,especially the long tube is prone to global buckling instability,which makes it difficult to control the preparation of beneficial wrinkles.Regarding the issue above,we try to use the beneficial wrinkled parts by heating in selected areas,and with the help of a self-made axial compression experimental device that can realize the selected area heating of the tube.The distribution law of the axial non-uniform temperature field of the tube during the induction heating process and the wrinkling behavior of thin-walled tube and the distribution law of property and microstructure of wrinkled parts were systematically investigated by using a combination of numerical simulation and experiment.It explored the feasibility of prefabricating beneficial wrinkled tube parts under non-uniform temperature field.In order to obtain the mechanical properties and true stress-strain curves of the AZ31 B magnesium alloy and 5052 aluminum alloy tubes,the uniaxial tensile experiments are carried out under different strain rates and different temperatures.The finite element model of selective induction heating and axial compression wrinkling of tubes was established by using BEM in DEFORM-3D software.An experimental device for axial compression that can realize selective induction heating of tubes was designed.The induction heating and axial compression process of thin-walled tubes was studied by simulation and experiment.The axial temperature field distribution of the tube was obtained.The results showed that induction heating can make a non-uniform temperature field with the highest temperature 10 mm above the center point in the axial direction of the tube,and the temperature decreases toward both ends.As the central temperature of the heating zone increased,the axial temperature difference of the tube decreased.The GaussAmp function can be used to quantitatively characterize the shape and size of the axial cross-sectional profile of the wrinkles.The wrinkling behavior and the evolution of the wrinkle shape of the tube under different parameters such as temperature field,axial compression and axial compression speed were analyzed.The results showed that at 200?and above,as the temperature increased,the wrinkle height and width of AZ31 B magnesium alloy tubes gradually increased.For 5052 aluminum alloy tubes,as the temperature changes,there was no effect on the wrinkle width,and the wrinkle height was gradually increasing.With the increasing of the axial compression,the wrinkle height of AZ31 B magnesium alloy and 5052 aluminum alloy tubes gradually increased,and the width gradually decreased.With the increasing of the axial compression speed,the wrinkle height of the tube gradually increased,while the change rate of the wrinkle width was smaller.Under the same conditions,the wrinkles of 5052 aluminum alloy tubes with larger yield strength,elastic modulus and poor plasticity were higher and thinner than those of AZ31 B magnesium alloy tubes.The wrinkling mechanism of thin-walled tube under non-uniform temperature field was revealed.When the central temperature of the heating zone is lower,the axial gradient of the temperature field is small,and the tube compression occurs as a whole.When the temperature in the center of the heating zone rose,although the diameter of both ends will increase,there will be a small wrinkle in the middle.As the temperature continued to rise,the axial temperature gradient is larger,and an overall axisymmetric wrinkle would be formed in the axial high temperature area of the tube.The distribution laws of the wrinkles' wall thickness,microstructure and microhardness were analyzed.The results showed that the tube wrinkle has obvious thickening phenomenon,in which the thickening rate was the largest at the peak of the wrinkle,and the thickening rate was the smallest at the half-height width of the wrinkle.With increasing of the axial compression,the wall thickening rate at the peaks of wrinkle gradually increased.After the axial compression deformation and wrinkling,the grain size of the tube wrinkle became smaller,and the average grain size at the peak of the wrinkle was the smallest.With the increasing of the axial compression and the temperature,the Vickers hardness value of the wrinkle was generally decreased.And the Vickers hardness value at the half-width position of the wrinkle was relatively smaller than those at the peak position and the valley position.