Optimum Design Of Impact Energy Absorption Performance Of Thin-walled Tube Processed By Surface Nanocrystallization

With the continuous improvement of China's economic level,the construction of domestic road traffic is becoming more and more perfect,and the number of cars is increasing year by year,which greatly facilitates people's lives,but traffic safety issues also cause lives and property loss.In a collision accident,the use of energy-absorbing structures can effectively absorb and dissipate the huge kinetic energy and decrease impact force in the impact collision process,reducing the loss of life and property.The thin-walled shell structure absorbs a lot of energy through the collapse of the structure when it is impacted,and has the characteristics of light weight and excellent price,and is widely used in the design of energy absorbers.In this paper,surface nanocrystallization is applied to the improvement of the energy absorption performance of thin-walled square tubes.It is proposed to enhance the surface of the thin-walled square tubes by localized nanocrystallization to control the buckling deformation mode of the structural crushing process to improve the overall energy-absorbing performance.In contrast to traditional methods such as prefabricated indentation,initial shape and additional structure,the surface nanocrystallization technology does not change the structure size and configuration,and is easy to process.In this paper,the following research results are obtained through experiments and numerical simulations:(1)An experimental platform for surface nano-treatment of 304 stainless steel sheet was built,and through the static tensile test of metal at room temperature,it was found that after ultrasonic nanocrystallization,the plastic tensile strength of 304 stainless steel sheet was increased by 131.13%,reaching 499.47 MPa,but The elastic modulus decreased by 19.98% to 144.20 GPa.(2)The energy absorption performance of the centered single-stripe annular surface nanometer square tube under different nanocrystallization area ratios was analyzed,and it was found that the full nanocrystallization design will greatly increase the peak impact load,which is not conducive to protecting the people and things behind;while the square tube without nanocrystallization has an obvious upward trend in the later stage of impact,and the energy absorption performance is poor.The energy-absorbing square tubes with mixed layout of nanocrystallization and non-nanocrystallization can well avoid excessively high impact peak load,and the higher the ratio of nanocrystallization area,the better the overall energy absorption performance.For the square tube with rectangular nanocrystallization on the surface,the effect of the distance between the rectangular nanocrystallization area and the edge on the overall energy absorption performance of the other tube is analyzed.It is found that the square tube with the nanocrystallization treatment of the rectangular area on the edge is more energyabsorbing effective.(3)Optimize the single-strip ring-shaped surface nanocrystallization square tube with an area ratio of 40%,and take the height of the stripe from the bottom of the square tube as the design variable to maximize the total energy absorption.The obtained optimal solution of impact load efficiency CFE is 44.25% higher than that of the non-nanocrystallization square tube;the total energy absorption and specific energy absorption SEA is 45.84% higher than that of the nonnanocrystallization square tube.The optimal solution is only surface nanocrystallization with a 40% area ratio but its energy absorption is higher than the centered single-stripe square tube with a total of more than 80% area,and is only slightly lower than the full nanocrystallization square tube.The overall energy absorption performance is well enhanced.(4)Considering that distributing more nanocrystallization areas on the edges can effectively improve the energy absorption performance of the tube structure,the design of an isosceles triangle component with the bottom edge close to the edge is proposed based on the Moving Morphable Components(MMC)framework.Under this optimization framework,the square tube with three moving morphable components is optimized to maximize the total energy absorption,and the nanocrystallization area ratio is restricted to 40%.Obtained better results than the single-strip optimal solution,and its total energy absorption performance even exceeded the full nanocrystallization square tube.