Study On Inducing Buckling Modes Of Square Thin-walled Tubes By Technology Of Surface Self-nanocrystallization

Collision and impact are popular problems in the transportation and construction. How to protect safety of human being as well as the important equipment becomes the primary task in the studies of those areas. One of the effective methods is configuring the energy-absorbing structure. Since the global and local buckling of the closed thin-walled structures occurs when impact loads are acting on the end of the structures, most of the impact energy is absorbed into the buckled structures. Moreover, the thin-walled structures have many advantages, such as light weight, low cost. Therefore, the thin-walled structures are widely used in major energy-absorbing structure or device. The magnitude of energy absorption effect of such structures depends on the order of buckling modes and the history of the buckling process. Researchers keep working on the topic mention above without interruption, and the traditional pre-indentation, the initial shape and additional buckling mode to control and design the energy-absorbing structures were usually used in their studies. In this thesis, the traditional research methods are break through, and a new technique of surface self-nanocrystallization is firstly introduced to the thin-walled structure design. By applying the technique of surface self-nanocrystallization on the thin-walled surface energy absorbing structure, the local surface mechanical properties are changed. It provides a way to improve the absorbing effects by inducing high-order buckling mode and controlling of the buckling history of square thin-walled tube buckling modes. Finally, a new method for inducing the buckling modes of thin-walled tube and designing energy-absorbing structures is proposed.In the paper, the finite element method is used to perform the numerical simulation and the conclusion are listed as follows:(1)In the study of inducing buckling modes of a square thin-walled tube by the local surface self-nanocrystallization(LSSNC) layout acting on, it can be found that, the symmetric and anti-symmetric LSSNC which are applied on the thin-walled square tubes induces a steady progressive buckling modes and greatly improves the energy-absorbing properties. Through the analysis of the influence of different divisions and degrees of LSSNC on the buckling modes and energy absorbing properties of thin-walled square tube, the results shows that the number of different circular division directly affects the fold number of buckling mode and the degree of LSSNC impact energy absorption performance. (2) In the study of inducing buckling modes of thin-walled square tube under the axial LSSNC, it can be found that, the induced buckling modes will contain distorted mode and become unstable when an even number of equally spaced LSSNC layout in the axial direction on each surface of the thin-walled square tube.; the induced buckling modes will emerge stable stacked buckling mode and improve the energy absorption effect when an odd number of equally spaced LSSNC layout in the axial direction on each surface of the thin-walled square tube.(3) In the study of the induction of buckling modes of thin-walled tube under the oblique strip and squared LSSNC, the stable telescoping torsional buckling modes can be induced by making oblique strip LSSNC to thin-walled tube, and a high-level form of buckling modes can be induced by using a squared LSSNC layout.(4) In the study of the buckling modes of square thin-walled tube under many degrees LSSNC, it is found that a compact thin-walled square tube buckling modes and buckling history can be induced by making different degrees LSSNC on the thin-walled square tube.. It provides a new design idea to control buckling modes of structures and energy absorption level.