2013 International Conference on Aerospace Science & Engineering (ICASE)

978-1-4799-0993-3/13/$31.00 © 2013 IEEE

Numerical Investigation of Usage of Patterned Collapsible Energy Absorbers in Steering Column of

an Automotive Vehicle Zeeshan Qaiser1, Omer Masood Qureshi1, Khalil Aslam Awan2, Hassaan Ahmed2

2Department of Aeronautics & Astronautics, Institute of Space Technology, Islamabad, Pakistan 1Department of Mechanical Engineering, Institute of Space Technology, Islamabad, Pakistan

Abstract----Collapsible energy absorbers are encouraged in the field of automotive in the past decade due to their good energy absorption characteristics. Impact energy absorbers dissipates maximum amount of energy during an axial impact. Impact of steering wheel with ribs of driver during an accident is an area of prime concern. A patterned steering column is proposed in the present work which turns into inverting tube and absorb good amount of energy during an accident. The inversion process is induced in steering column by embedding sinusoidal patterns over it. This process is numerically investigated by using commercially available non-linear solver LS-DYNA (TM). Different steering column arrangements are studied and force-displacement results are analyzed in this work. A study is performed to investigate and compare energy absorption parameters of conventional and proposed design of steering column. The results show that the energy absorption with proposed sinusoidaly patterned steering column is better than conventional steering column

Keywords—automotive crash absorbers; energy absorption

I. INTRODUCTION Automotive crash absorber is a system which dissipates impact energy into elastic and plastic form of energy. Aluminum crash absorbers are of prime importance in this regard as they have high strength to weight ratio and high stiffness values. These properties of aluminum make it a befitting choice for crash absorbers. Circular tubes are one the major structural member in many automotive applications. There are many collapse modes which are undergo by tubes under axial collapse like crushing, flattening, splitting and inverting tube formation. Steering column of steering assembly is facing a practical problem as during its impact with ribcage of driver during an accident it must go inward. This problem is addressed by automotive manufacturers by placing two columns above each other. During impact loading one steering column goes into other so that it doesn’t harm the ribcage. The collapse strength of steering column is usually kept lower than the strength of ribcage. Alexander [1] in his fundamental study established a basic expression for average crushing load. Mamalis et al. [2] worked on the improvement of modeling of concertina mode of deformation for frusta and tubes. They performed certain experiments and showed good degree of agreement with the results of analytically derived expressions. The phenomenon of inverting tubes formation under axial loading was discussed in literature by Al Hassani et al. [3].

In this mode of deformation a constant load curve is obtained due to process of inversion. Chirwa [4] studied the analytical and experimental results of tapered tubes and it is concluded that tapered tubes with inversion phenomenon absorbs more energy than circular tubes with inversion keeping the thickness constant. Kinkead [5] analyzed the energy absorption characteristics during inversion process.

Patterns were first discussed in literature by X. Zhang et al. [6] they used triangular patterns and significantly increased the energy absorption. W. Jiang et al. [7], created a surface by adding a sinusoidal pattern but the energy absorption is marginally decreased.

Qureshi & Bertocchi [8] studied different patterns in which two frequencies are multiplied to obtain bidirectional patterns. Different patterns are studied in their work and they used various types of bi-directional patterns on aluminum box beams crash absorbers. In the successive study, Qureshi & Bertocchi [9] efficiently proposed a triggering mechanism by marginally altering the pattern over the length of the beam.

Inverting tube formation is dependent on die radius of tube. If the value of die radius is very small tube will undergo in progressive collapsible modes while when the radius is larger than a specific value it will collapse in the splitting mode.

The collapse of circular cylindrical tubes under axial loading is one the major problem in the analysis of automotive crash absorbers. From the point of view of energy absorption in automotive industry it was found that circular tubes under axial loading is the befitting choice. Circular tubes are also of importance because they provide a very constant absorption of force. In many industrial applications there is a requirement that the force absorption must be constant along a certain range of deformation.

The steering column used in automotive industry is a multipurpose thing which is used primarily to connect steering wheel with the steering assembly and it transfers the torque provided by driver. Besides its primary function of transferring the torque steering wheel also serve as a crash absorber in the case of frontal impact.

The definite aim of this research is to discuss the feasibility of utilizing patterned tubes as steering column in automobiles.

The buckling behavior depicted by simple tube is of concertina mode of deformation which is a type of progressive collapse.

II. MODEL SETUP

The Axial loading model on a steering column is setup using modeling conditions. In the setup shown in figure 1, a rigid wall with a velocity of 15.67 m/sec and a top rigid link with a constrained motion are used.

A planar rigid wall is incorporated at the bottom of the model. The contact surfaces are simulated as frictionless in this setup. Finite element model is of length 600mm with mesh size of 1mm * 1mm as shown in Fig. 1.

LS-DYNA [TM] is a very efficient and effective tool for the crashworthiness and analysis involve large deformations and changing boundary conditions.

LS-DYNA [TM] is an explicit dynamic solver. LS-DYNA [TM] is used to investigate and simulate the problems which we encounter in our daily life.

These problems are characterized by the involvement of large deformations, small time intervals in which these deformations take place. The salient features of LS-DYNA [TM] are that it involves the definition of contacts. One of the other major advantages of LS-DYNA [TM] is that it includes a large library of element and excellent collection of materials ranging from solids to the composites.

The solution technique which is utilized by LS-DYNA [TM] is explicit one. Explicit method is developed in order to deal with the complex dynamic problems in which there are deformations of bodies.

The main concept behind this explicit technique is that the parameters such as velocity and accelerations in a specific time is taken as reference and assigned as constant. These values are taken as constant for a specific time increment. These constant values are then utilized to solve the solution for the next time interval. In order to perform that action a very famous time integration technique is used which is central difference technique.

The material which is used is Al6260-T6, with Young's modulus E of 75 GPa, Poisson ratio � of 0.3, nominal flow stress of 0.326 GPa, with values of material constants A, B, C and n are 0.4, 0.22154, 0 and 0.6, respectively. Different control cards are written in LS-DYNA [TM] keyword file. Rigid wall is placed on the bottom of model in order to have better simulation of conditions. Control card for termination of simulation is also used.

III. RESULTS AND DISCUSSIONS After preparation of input keyword file solution is performed and post-processing of data is done by using LS-PrePost [TM] which is a post-processor for solution files of LS-DYNA [TM].

LS-PrePost [TM] is fully supported for the input keyword files which are being used in LS-DYNA [TM] in order to perform the solution.

Fig. 1. Finite element model

Fig. 2. (a, b, c) Deformation of reference steering column atdifferent intervals

(a) 10sec (b) 20sec

(c) 30 sec

Once the solution is run in LS-DYNA [TM] solver it gives a d3plot file which once again imported in LS-PrePost [TM] for the further post processing. Fig. 2 (a, b, c) depicts the deformation of simple steering column at different time intervals (10sec, 20sec and 30sec), tube under axial loading conditions described in section 2. Once the reference solution is obtained next step is to induce bi-directional patterns in the reference beam.

These patterns are created by multiplying two frequencies one frequency change along the cross-sectional circumference and other frequency change along the length of the hollow tube.

Similar loading conditions and material cards are employed on this new patterned beam which is discussed in section II.

After many iterative processes there was a pattern in which the tube undergoes the process of inversion.

This process is of prime importance as it reduces the initial force spike and increases the average crush load as shown in table I.

Reaction force is one the prime concern as its initial force spike must be reduced in order to have low impact on the ribcage by the steering column. As shown in figure 4 & 5 there is a significant decrease in the initial force spike of reaction force. There is a decrease of initial force peak from 230KN to 184KN.

Average crush load is also a major parameter because it tells about the average reaction force which a specimen can have throughout the simulation. To increase average crush load is also an area of prime concern. It is increased from 67KN to 92KN in the case of patterned beam. If plot of reaction force and time is critically analyzed it is evident that the variation in the average crush load in the case of patterned steering column is less than the variation in reference beam model.

Model Initial Peak (KN)

Average Crush load (KN)

Total Energy Absorbed at 30 sec

(KJ)

Reference Model

230 67 30

Patterned model

184 92 41

(a) 10sec (d) 20sec

(b) 30sec (c) Top view

Fig. 3. (a, b, c) Deformation of reference steering column at differentintervals (d) Top view of inverting tube

Table I. Comparison of different parameters of reference and patterned steering

Fig. 4. Reaction force vs. time of reference beam

Fig. 5. Reaction force vs. time of patterned beam

Energy absorption is also a very good indicator of performance of crash absorbers. When an impact occurs initially kinetic energy is all energy system possess as time proceeds the kinetic energy is converted into internal energy. This increase in internal energy further causes a change in internal forces which in turn produce stresses and deformations.

Fig. 6 and 7 depict how two different forms of energy (kinetic energy and internal energy) change with respect to time. Internal energy absorption is a prime indicator in this scenario. In the case of patterned steering column the energy absorption is better and maximum energy absorption at 30sec is 41KJ while at same time interval the energy absorption in reference steering column is about 30KJ.

IV. CONCLUSION

Addition of patterns to the steering column of a vehicle had significantly improved the performance of steering column when it is used as a crash absorber. Inverting tube is formed as a result of embedding bidirectional pattern on a model of steering column. A decrease of about 20 percent in initial force spike is noted in the most optimal case. Average crush load is also increased about 37 percent as it increases the energy absorption capabilities of circular tube. An increase of about 36.67 percent in energy absorption is also achieved by embedding patterns. The results provided in this work may further be utilized to use patterned tubes in the steering column of automobiles.

REFERENCES [1] J. M. Alexander. “An approximate analysis of the collapse of thin

cylindrical shells under axial loading,” Quart. J. Mech. Appl. Math. vol. 13, pp. 10-15, 1960.

[2] A. G. Mamalis, D. E. Manolakos, G. L. Viegelahn, and W. Johnson. “The modelling of the progressive extensible plastic collapse of thin-wall shells,” Int. J. Mech. Sci. vol. 30, pp. 249–61, 1988.

[3] Al-Hassani, W. Johnson, and W. T. Lowe. “Characteristics of inversion tube under axial loading,” J. Mech. Engg. Sci. vol. 14, pp. 370–81, 1972.

[4] E. C. Chirwa. “Theoretical analysis of tapered thin-walled metal inverbucktube,” Int. J. Mech. Sci., vol. 35, pp. 325–351, 1993.

[5] A. N. Kinkead. “Analysis for inversion load and energy absorption of a circular tube,” J. Strain Analys. vol. 18, pp. 177–88, 1983.

[6] X. Zhang, G. Cheng, Z. You, and H. Zhang, “Energy absorption of axially compressed thin-walled square tubes with patterns,” J. Thin Wall Struct. vol. 45, pp. 737–746, 2007.

[7] W. Jiang, and J. L. Yang, “Energy-absorption behavior of a metallic double-sine-wave beam under axial crushing,” J. Thin Wall Struct. vol. 47, pp. 1168–1176, 2009.

[8] O. M. Qureshi, E. Bertocchi, “Crash behavior of thin-walled box beams with complex sinusoidal relief patterns,” J. Thin Wall Struct. vol. 53, pp. 217–223, 2012.

[9] O. M. Qureshi, E. Bertocchi, “Crash performance of notch triggers and variable frequency progressive –triggers on patterned box beams during axial impacts,” J. Thin Wall Struct. vol. 63, pp. 98-105, 2013.

Fig. 7. Energy plots of patterned beam

Fig. 6. Energy plots of reference beam