The Behaviour of Thin-Walled Cylinders with Reinforcing Inner Walls Subjected to High-Velocity Impact

Thin cylindrical tubes as impact energy absorbers have been widely used in various fields. Previous researchers have proposed many methods to increase the ability to absorb energy by modifying the geometry or using different materials. This study discusses using reinforcing walls in the cylinder to increase energy absorption capability. We make thin cylindrical specimens made of aluminium alloy with a length of 150 mm, a diameter of 50 mm, and a thickness of 1 mm. Reinforcing walls are fitted in the cylinder with a vertical position of 1, 2, 3, and without supporting walls. An impactor moving at high velocity hits the up-end cylinder in the axial direction. The finite element method modelling results show that installing reinforcing walls in thin-walled cylinders increase the maximum impact force, decreases the maximum deformation, changes the deformation mode, and increases the energy absorption capability. The amount of wall added to the thin wall will affect the impact behaviour of the specimen. However, in this study, the presence of a wall will have an effect when the deformation reaches the location of the wall. Nevertheless, using this reinforcing wall also makes the manufacturing process more complex. Therefore, this study’s results are recommendations for the design of the impact energy absorption structural system.


Introduction
Many methods are proposed to reduce the impact energy due to a collision between one object and another.Modifications are made by creating various shapes that increase the ability to absorb energy [1].Thin-walled structures are well-known absorbers of impact energy.The study of the advantages of this structure proves its ability when subjected to impact loads under quasi-static and dynamic conditions [2].Thin cylindrical structures are excellent energy absorbers at high-velocity impact, and increasing the impact velocity will increase the peak of the reaction force [3].Modifications to the tube wall were also carried out to improve the performance of the structure, namely by forming a tapered angle [4], [5], installing ribs on the outer wall [6], installing end caps at the end of the tube [7], modification of corrugated tube [8].The shape of the different cross-sections also affects the impact behavior of a thin tube [9], [10], [11].
However, circular cross-sections proved to be the most effective in absorbing energy [12], [13].Filling the thin-walled structure with rubber increases the energy absorption ability on straight cylinders [14], [15].Or conical [16].The rubber in the tube will expand the plastic deformation part and change the deformation pattern from non-axisymmetric to axisymmetric.In practice, impact structures are widely used for automotive purposes.Car collisions must be suppressed to reduce the effects of death on passengers.The analysis must be conducted in static and dynamic conditions [17].Deformation that occurs in the chassis of an automobile must encounter specific requirements [18].Automobile crashworthiness can be controlled in various collision situations to increase safety [19].
This study aims to obtain an increase in the ability of the impact behavior of thin tubes by forming thin-walled perpendicular to the tube walls.In previous studies, the honeycomb form has been investigated [20].The installation of this bulkhead is compared with a tube without a bulkhead for comparison.

Methodology
This study uses the finite element method to model the specimen and the collisions that occur.Modeling using the finite element method is often used in research related to impact analysis [21], [22], [18].
We use Aluminum Alloy to make the specimens, 2770 kg/m3 of density, Poisson ratio 0.33, and modulus of elasticity 7.1 x 1010 Pa.The impactor is made of steel with a density of 7885 kg/m3 and weighs 1 kg.The form of the specimen is as follows.

Results and Discussion
Four specimens, SP0 (without bulkhead), SP1 (with one bulkhead), SP2 (with two bulkheads), and SP3 (with three bulkheads), were given an impact velocity of 50 m/s with a 1 kg steel impactor.A comparison of deformation histories is as follows.In Figure 6, it can be seen that the more bulkheads, the greater the maximum reaction force.The bulkhead will increase the strength of the specimen so that the first wrinkle formation process will be even greater.The maximum energy absorbed in all specimens tends to be constant due to the same kinetic energy received by the models.
The stroke efficiency decrease further with the addition of the bulkhead.All specimens have a non-axissymmetric pattern due to the large ratio between the radius and the thickness of the cylinder walls.

Conclusion
The addition of a bulkhead on the cylinder has the following impact: 1.The deformation is getting smaller.2. The reaction force is getting bigger.
3. Stroke efficiency is getting smaller.4. The total absorbed energy tends to remain.The results of this study are a consideration in the manufacture of energy-absorbing equipment.

Figure 2 .
Figure 2. Simulation Method Impact velocity = 50 m/s.Fixed support is apllied at the one end of specimen.

Figure 7
Figure 7.Total Energy