## 2 Geometry and Finite Element Modeling
### Finite Element Modeling  
The LS-DYNA software (R12.1) was used to simulate the mechanical behavior of the shrink tube during the collision process. The shrink tube was a deformation component. The \"Mat.24\" material was used to simulate 45 steel, and the \"Mat.20\" material was used for other components. According to the material testing standard [38] (ISO 6892-1:2009, MOD) [39], the MTS 647 hydraulic wedge clamping tensile testing machine was used to conduct a quasi-static tensile test to obtain the mechanical property curve of 45 steel. The test equipment and specimen clamping status are shown in Figure 2a. The test was conducted at room temperature and the tensile speed was 2 mm/min. The standard size of the material sample is shown in Figure 2b, and the fracture sample and the true stress-strain curve are shown in Figure 2c. Among them, the material parameters for 45 steel were as follows: a density of 7850 kg/m\({}^{3}\), a Poisson's ratio of 0.3, an elastic modulus of 206 GPa and a yield strength of 367 MPa.  
The finite element model was consistent with the real test scenario. An anti-climb device was installed at the front end of the test trolley, which hit a fixed rigid wall at the required mass and speed. The finite element model was established, as shown in Figure 3. In order to take into account both calculation accuracy and calculation efficiency, a convergence analysis was performed, as shown in Table 1. The size of the shrink tube and the shrink mold flange was selected to be 3 mm for meshing, a size of 5 mm was used for other parts of the anti-climb device and a size of 30 mm was used for the trolley. The collision test finite element model after meshing had a total of 518,540 nodes and 454,685 elements. Automatic face-to-face contact was set between the contact surfaces of the components, with both the kinetic friction coefficient and static friction coefficient set to  
Figure 1: Structure description of the shrink tube anti-climb device: (**a**) installation diagram; (**b**) size detail drawing; (**c**) axonometric drawing; (**d**) semi-sectional view.  
in the impact force. A high-speed photography system was installed directly above and on the side of the impact position to record deformation images and displacement data during the impact. The mass of the test vehicle was 27 t and the impact speed was 3.64 m/s.  
The deformation sequence, as well as the force and displacement curves under test conditions and simulation conditions, are shown in Figure 5. It can be seen that the test curves and simulation curves were in good agreement, and the deformation process of the shrink tube was smooth and orderly. The final displacements of the test and simulation after the collision were 303.64 mm and 307.86 mm, respectively, with a relative error of 1.39%. The energy absorption values of the test and simulation were 175.55 kJ and 178.87 kJ, respectively, with a relative error of 1.89%. The average forces of the test and simulation were 578.15 kN and 581.01 kN, respectively, with a relative error of 0.49%. The results of the experimental mean force and the simulated mean force in this model were almost consistent. This indicates that the finite element model is reliable and effective and can be used for subsequent research.  
Figure 4: Test scenario.  
Figure 5: Shrink tube deformation plots and force versus displacement curves: (**a**) test deformation diagram; (**b**) simulation deformation diagram; (**c**) comparison of simulation and test force and displacement curves.