Superelastic Characteristics And Bufferring Performance Of NiTi Shape Memory Spring

NiTi shape memory alloy has a broad application prospect in the field of energy absorption and shock absorption due to its ability to produce large recoverable strain due to hyperelasticity and shape memory effect.This article USES the method of combining the cold drawing and annealing was prepared by a diameter of 1.2 mm of Ni Ti alloy silk,the heat treatment involution gold martensite phase transformation behavior,organization structure,super elasticity and the influence of the shape memory effect,using the optimal heat treatment parameter of wire winding spring,the spring heat treatment parameters and super elastic properties and buffer can absorption performance,The spring is assembled in the buffer,the energy absorption performance of the buffer is studied,and the application of shape memory alloy spring in aerospace buffer is explored.The wire with diameter of 1.2 mm was successfully prepared by cold drawing method.After annealing at 450?,the hyperelasticity and shape memory effect were recovered.After annealing at 450? for 90 min,the nanocrystalline microstructure of the cold drawn wire was obtained.The nanocrystalline size of the hyperelastic drawn wire was 30-50 nm,and that of the memory effect drawn wire was 20-30 nm.The spring with certain parameters was successfully wound by the designed lathe spring winding device,and the hyperelasticity and shape memory effect of the spring were recovered after annealing at 450? for 90 min.When the spring index is at least 6,the spring has the best superelasticity,memory effect and energy absorption.At room temperature,the strain rate has no effect on the spring performance.At 45?,the superelastic spring is in complete austenitic state and has good superelastic cycling stability.When the displacement is 120 mm,the energy absorption Wm of the unit mass of the memory effect spring is 0.31 J/g,and the single Wm of the superelastic spring is0.9 J/g.The strain rate has no effect on the energy absorption Wm per unit mass of the spring with a spring index of 6 prepared by the 2mm diameter alloy wire.When the displacement is 120 mm,the superelastic unit mass energy absorption Wm is 1.21 J/g,and the memory effect Wm is 0.32 J/g.With the increase of temperature,the superelastic spring gradually loses its superelasticity,and the internal and external tissues of the failed spring are austenite phase.The maximum service temperature of the superelastic spring cannot exceed 45?.When the spring index is both 6,the unit mass energy absorption Wm of the spring wound by 1.2mm spring wire is lower than that of the spring wound by 2.0mm spring wire.Therefore,the spring wound by 2.0mm spring wire diameter is selected to assemble in the buffer.Under static load test conditions,the strain rate has no effect on the hyperelastic buffer unit,and the energy absorption of the buffer conforms to the parallel design of the spring.With the increase of strain rate,the mechanical properties and energy absorption capacity of the memory effect 1:1 are slightly increased.Under the impact load test,the energy absorption of the super elastic 1:5 reduction test piece is ?56 J when the buffer stroke is 60 mm,and the load of the platform is about1.14 k N.It can meet the technical requirements if it is assembled as a 3:5 test piece,that is,each layer of spring is added to 12.The memory effect is 1:1.The absorbing energy of the test piece is 90.8J according to the preload calculation method,84.2J without the preload calculation method,and the platform load is about 1.00 k N,which all meet the requirements of the buffer design.