Research On Seat Belt Pre-tension And Energy Absorption Characteristics Based On Shape Memory Alloy

Active seat belts can improve occupant protection by accepting pre-collision signals and eliminating the gap between the occupant and the seat belt before a collision occurs.However,the existing active seat belts are mostly driven by gas explosion or DC motor,which have the problems of large volume and complex structure.The use of shape memory alloy（SMA）as the driving element of seat belt preload can not only exert its advantages of small size and simple structure,but also the energy absorption characteristics of SMA can absorb part of the energy transmitted by the occupant to the seat belt in the collision.Reduce occupant injury.Aiming at the shortcomings of the existing gas explosion-driven or motor-driven seat belt pre-tension mechanism,which has a complex structure and cannot be reused,it is proposed to apply shape memory alloy material to seat belt pretensioning and energy absorption,which will affect the SMA restoring force.The key parameters of the driving stroke are experimentally studied;at the same time,the energy absorption characteristics of the SMA during the impact of the seat belt are experimentally studied.The main contents are as follows:The basic parameters of SMA are experimentally measured,and the characteristic parameters such as phase transition temperature,elastic modulus,phase transition stress and maximum recoverable strain are obtained,which provide parameter basis for subsequent experiments and simulations.By heating the SMA wire to different temperatures and then performing quasi-static stretching,the difference in energy absorption between martensitic SMA and austenitic SMA is obtained.The results show that the energy absorption density of austenitic SMA under quasi-static stretching conditions is about Twice as long as SMA.The quasi-static tensile simulation of martensitic SMA and austenitic SMA was carried out respectively.Comparing the obtained simulation results with the experimental results,the error of the two energy absorption density data was less than 10%.The effects of the stiffness and preload of the bias spring on the driving force and driving displacement during the recovery process of the SMA are analyzed through experiments.The results show that the difference between the maximum driving force that the SMA can achieve is positively correlated with the stiffness of the bias spring.The size of the initial preload has no effect on the difference.And increasing the bias spring stiffness has little effect on the displacement and speed of the SMA end,and the driving stroke can recover 80% of the prestretched length.The seat belt pretensioning mechanism based on SMA is designed,and the driving force and driving stroke of the pretensioning mechanism are experimentally studied.The results show that the driving force loss caused by the internal structure of the pretensioning mechanism is within 15% while the space occupation is greatly reduced.,the loss of the end drive stroke is no more than 10% compared to the SMA linear arrangement.Design and build a seat belt impact test bench,and conduct impact tests when the seat belt is connected in series with the SMA.The results show that the SMA has a significant slowing effect on the impact force and impact acceleration.The SMA wire used in the experiment can reduce the peak value of the impact force.Reducing it to 70%-80% when not installed can reduce the peak seat belt acceleration to 60-70%.Impact tests were carried out on SMAs at different temperatures to study the impact energy absorption effect of martensite and austenite.Martensitic SMA has better buffering effect on impact force.Finally,the impact energy absorption limit of SMA is tested.The results show that when the shape memory alloy wire is broken during impact,its energy absorption will be greatly reduced.