Study On Variable Stiffness Performance Matching Method Of SMAHC Helical Spring

The enormous potential of composite materials for lightweight in the automotive industry has attracted widespread attention.The combination of intelligent materials with composite materials constitutes a "structure-function" integrated intelligent composite material,which has broad application prospects in some scenarios that achieve both functionalization and lightweight.In order to meet the variable stiffness requirements of structures such as automobile suspension in different scenarios,this paper proposes to design a helical spring with active variable stiffness function and lightweight effect.The shape memory alloy(SMA)is embedded into the fiberreinforced composite material in the form of orthogonal weaving to make shape memory alloy hybrid composite(SMAHC)helical spring.In this paper,the variable stiffness performance matching method of SMAHC helical springs was studied through a combination of theory,experiment,and simulation.The main research contents are as follows:(1)The active variable stiffness principle of SMAHC structure was revealed.The SMA temperature was controlled by regulating the current.The temperature induced the transformation between the martensite phase and the austenite phase of SMA.And the active control of the structural stiffness was completed under the combined effects of the change of the SMA elastic modulus,the phase transition recovery force and the change of the thermal elastic modulus.The formula for calculating the elastic constant of hybrid orthogonal fabrics with different fibers was derived based on the micromechanics and mixing criteria of composite materials.The concept of equivalent stiffness was proposed by using the phenomenological method according to the variable stiffness constitutive model and variable stiffness principle of shape memory alloy hybrid composites.(2)A stiffness prediction model for SMAHC helical spring was established.The structural design of SMAHC helical spring was carried out from the perspective of SMA implantation method and spring structure size.Based on the analysis of the active variable stiffness principle and force analysis,a spring stiffness prediction model that included different SMA phase transition stages was constructed to clarify the spring variable stiffness regulation mechanism.The spring wire was made by hybrid braiding of SMA and reinforced fiber.The SMA occurred phase transition under the temperature excitation.The percentage change of SMA martensite and the temperature change of the spring body bring about the spring stiffness change,which was divided into three stages in the process of heating up and cooling down respectively.(3)The driving torsion law and torsional variable stiffness performance of SMAHC tubes facing the torsion characteristics of spring wires under thermal excitation were studied through a combination of experiment and simulation.The ability of SMA to drive torsion of tubes increased with the increase of phase transition recovery force.The driving recovery force can be controlled by changing the number of embedded SMA,the number of heated SMA and the heated temperature.The direction of embedded SMA determined the direction of recovery force,thereby affecting the control effect of torsional stiffness.The torsional stiffness changes of tubes under different variables were compared and analyzed.The results showed that changing the number of embedded SMA within a certain range had the strongest control effect on torsional stiffness,followed by the number of heated SMA and the direction of embedded SMA.The weight of each index in the variable stiffness evaluation model was determined using Analytic Hierarchy Process.(4)The driving performance and variable stiffness performance of SMAHC helical springs under thermal excitation were studied by combining experimental and theoretical methods.In the phase change temperature range,the axial driving effect of SMA phase transition recovery on the spring increased with the increase of heated temperature.When the SMA was embedded forward,the phase transition stress increased the spring stiffness.On the contrary,when the SMA was embedded reversely,the phase transition stress reduced the spring stiffness.The modulus of SMA after phase transformation,the modulus of matrix softening and the coefficient of phase transformation recovery force were obtained through experiments,which were used to calculate the spring stiffness after SMA being heated.Based on the above series of research results,the SMAHC helical spring was applied to the working scene of automobile suspension,and the variable stiffness performance matching method was clarified from the design aspect and the control aspect.This study provides a new idea for the application of shape memory alloys in rotary composite structures.The research results can be used for adaptive control of stiffness and vibration characteristics of rotary composite structures.It provides important references for the application and development of shape memory alloy hybrid braided composites in the field of springs.At the same time,it provides a novel and effective method for controlling the variable stiffness characteristics of torsional structures with lightweight effects.