Research On The Characteristics Of Automotive Energy Absorption Device With Shape Memory Alloy

Vehicle safety issues are directly related to the safety of human life and property,and has been highly valued by the consumers and researchers.In order to improve vehicle safety,some of the traditional energy-absorbing materials and structures are widely used in the field of automotive passive safety.But by the principle of lightweight vehicle,the role of these energy-absorbing materials and structures are subject to certain restrictions.In recent years,the emergence of intelligent materials and intelligent structures provides a new way to solve the contradiction between vehicle safety and light weight.Shape memory alloy(SMA)is one of the most popular intelligent materials,and has many excellent mechanical properties,such as low density,high energy consumption,impact resistance and corrosion resistance.The shape memory alloy used in the field of automotive safety as buffer and energy absorbing material can effectively improve and enrich the effort of energy-absorbing and protection during collision events.In this paper,energy-absorption properties of both martensitic and superelastic Ni Ti wires are studied in quasi-static conditions.According to that,Ni Ti SMA wires are used in a two – level energy-absorption device as energy-absorption materials and the experiment and simulation of the energy-absorption device are carried out.The main work of the paper is shown as follows:(1)The stresses and temperatures of phase transformation for both martensitic and superelastic Ni Ti wires are measured by tensile machine and differential scanning calorimeter;Three kinds of constitutive equation of SMA are introduced in brief;Those are prepared for the subsequent quasi-static tensile test and simulation analysis.(2)The quasi-static tensile tests of both two kinds SMA wires are carried out and the effects of strain amplitude,tensile rate,temperature and cyclic loading on the mechanical properties of SMA,especially the influence on the energy-absorption density are analyzed in detail.Then the quasi-static tensile simulations of those two SMA wires with different amplitude are carried out by ANSYS.The simulation results are in good agreement with the experimental results,and the overall error was controlled within 10%.The accuracy of the simulations are verified.(3)According to the stress-strain curves of SMA wires under fracture,the total energy required for SMA wires drawing are deduced by combining the formula of aluminum alloy fracture energy,and the energy-absorption density of each energy component is obtained.The results show that the energy dissipation density of martensitic Ni Ti SMA wire is much higher than that of superelastic Ni Ti SMA wire.(4)A new type of SMA two-level energy-absorption device is designed according to the deformation and energy-absorption characteristics of SMA wires,and the impact energy-absorption characteristics of the device are studied by experiment and simulation respectively.In this paper,a kind of impact test device for wire-materials is designed and constructed.Then both of martensitic and superelastic Ni Ti SMA wires are experimented at different impact mass conditions.The experimental results show that both SMA wires have good impact protection performance,and the energy absorption density of SMA wire increases with the increase of impact mass.Further,the secondary energy-absorption sleeve is simulated and analyzed.The results show that the multi-cavity structure composed of inner and outer sleeves is far superior to the traditional crash box in terms of total energy absorption and specific energy absorption.(5)The impact tests of martensitic Ni Ti SMA wires at different temperatures are carried out by using the SMA wire impact test device.The experimental results show that the temperature can effectively change the mechanical properties of SMA wire in a specific temperature range.In particular,the energy-absorption density of the martensitic SMA wire increases significantly as the temperature continues to rise.This fully validates that the SMA energy-absorption device can realize the intelligent control of energy-absorption and impact protection through certain control strategy.