INVESTIGATION OF CRUSHWORTHINESS OF
C-SECTION S-RAIL JEEP CHASSIS
Javad Marzbanrad1, Ali Kamyab2
marzban@iust.ac.ir ali_kmyb@yahoo.com
Iran University of Science and Technology,
Automotive Engineering Department,
Narmak, 16846-13114
Tehran, Iran
Abstract
In this paper crashworthiness of c-section s-rail jeep chassis modeled and analysis. Nowadays
safety is the most important factor that vehicle producers must be considered in their design. In
this paper effect of mass of striker, velocity of striker, strain rate, module of elasticity, yield
strength and material type studied for this analysis. The non linear large deformation finite element
method package (LS-DYNA) was used for modeling and analysis. The charts of energy absorption
vs. strain rate, module of elasticity, yield strength, striker mass and material type are represented in
this study. Finally, energy absorption and crashworthiness of Magnesium-Steel s-rail is achieved
to be best between other material types.
Keywords: biomaterial, s-rail, c-section shell, crashworthiness, energy absorption, front crash
1 INTRODUCTION
Nowadays vehicle safety is one of the most important problems in automotive industries. Accordingly,
vehicle producers pay a lot attention to safety standards such as FMVSS for reduction passenger injuries at
crush time. Increasing crush energy absorption causes more safety level for vehicle. Generally, safety is
related to three following items:
1- Road situation such as weather, asphalt situation, slope of road (gradient).
2- Driver and drowness of his\her.
3- Vehicle safety systems.
Passive systems act after accident and consist of two categories: 1- Absorber structure such as chassis,
bumper, hood and so on. 2- Safety belts, airbags, type of passenger seats.
In this paper, the goal is weight reduction that result to enhance efficient fuel consumption and
crashworthiness improvement to increase vehicle safety. Here, part of jeep chassis modeled as a s-rail and
analyzed. In general, bumper absorbs 19 percent of axial crash energy; courd and hood 30 percent and
chassis 50 percent. With structure design we can improve energy absorption.
Automotive crush simulation because of attention to occupant health at accident is very important. On the
other hand, impact energy absorption are widely used at many vehicle and mobile compartments such as
automobile, train, aircraft, ship, elevator and industrial machinery. Main goal of this absorber is minimize
system damage and assurance of safety.
One of the most used absorber is chassis and damper of vehicle. Vehicle structure that consists of chassis
and body must be designed so that prevents passenger injury and deformation of cabin. consequently, s-rail
has most important role in energy absorption. S-rail itself consists of three parts:
1- Soft zone that impact velocity must be less than 15 km/hr.
2- Rigid zone that impact velocity in this zone must be from 15 to 50 km/hr.
3- Hard zone that designed to prevents deformation of cabin. Impact velocity can be more than 50
km/hr at this zone.
Kim and Wierzbikci at 2001 year studied effect of structure cross section at deformation strength of one
s-rail (1). They at this research studied suitable ratio of s-rail dimension from view of crashworthiness and
weight efficiency; and then compare reinforcement profiles crashworthiness and profile filled with foam.
Their research shows that foam filled s-rail profiles with optimized thickness can enhance energy
absorption value to 200 percent rather than basis model.
Kim at 2002 year at his research studied new cross-section from aluminum alloy by numerical and
analytical method and investigated effect of energy absorption at this new cross-section (2).
Results of this research showed that 1.9 increase in value of energy absorption at new cross-section via
older cross-sections. "Thin structure act as absorbers" was paper title that write by Abramowitz (3). This
paper studied deformation mechanism of this shells and buckling of their according to special elements ("
super folding"). Closed loop solution for 3D response s-rail frames with rectangular cross section is
another research from Kim and Wierzbikci at 2004 year (4). This paper studied two directional bending of
s-rail and sensitive area around it.
Perfect plastic moment analysis with different rotational angles showed two modes of deformations. It
illustrated that critical aspect ratio for square profiles expect two deformation modes is 1.366.
2 PLASTIC BEHAVIOR OF C-SECTION UNDER STATIC LOAD
Plastic moment (M0) has a relation to the bending moment (MY) of c-section (5).
6 + 3λ Ht
M0 = M Y that λ = (1)
6 + 2λ 2 Bh
where H, t, B, h is shown in Figure 4.
3 ANALYTICAL RELATION FOR EXTREACT DYNAMIC MOMENT
Dynamic moment can be determined as the following equation using Figure 3.
x2 x2 x3 d 2w ∂M
M d = −p + m( − ) 2 + M 0 That at x=0: M=M0 =Q=0 (2)
2 2 6l dt ∂x
4 ENERGY ABSORPTION DURING IMPACT
If we neglect gravity acceleration during impact of striker to shell, we can model physical system as shown
at Figure 1. Consequently, basis of impact rules result:
M 2V2 = ( M 1 + M 2 )V3 (3)
where V3 is twins striker and cylindrical shell velocity. Energy absorbed with energy absorber between
two masses M 1 and M 2 is:
M 2V22 M
Kl = ( ) /(1 + 2 ) (4)
2 M1
where if M 1 or cylindrical shell mass be fix then K l , energy absorbed from axial crushing of cylindrical
shell, is:
M 2V22
( ) (5)
2
5 FINITE ELEMENT MODELING
Here the c-section s-rail jeep chassis modeled. A striker element is built by four nodes in corners of one
element with specific mass. Striker material changed from elastic to rigid at analysis process. This striker
with mass M2 and velocity V2 crushes with s-rail along Y axis. Contact type is surface to surface at
automatic option. S-rail modeled with 3340 elements and bi-material section meshed with different mesh
size; according to Figure 12. Selected element for analysis is shell 163.
6 RESULTS
The nonlinear and large deformation finite element model was used for the modeling and analysis of
energy absorption of thin s-rail shells after crash under axial impact. Results show that by decreasing of
size of elements to a certain value, stress and energy absorption become close to real values. Further
decreasing of element sizes does not have more effect.
With increasing of yield stress, energy absorption was decreased because of increasing of yield stress
leading to increase of module of elasticity (Figures 7 to 12).
The increase of module of elasticity caused absorbed energy to decrease due to the fact that strain energy is
reversed proportional to module of elasticity (Figures 7 to 12).
When strain hardening was increased the absorbed energy was decreased since s -e curve area after work
hardening is decreased (Figures 7 to 12).
If soft region of chassis built from Magnesium 80 percent reduction in weight via steel modeling gained.
Chassis built of bi-material is better than of single material chassis; they absorb more energy and have
more strength, less mass and reduction in fuel consumption.
Magnesium has higher weight reduction via steel material (table 2). Bi-material St-Mn has higher energy
absorption rather than other s-rails.
With improvement of S-rail material the cost will decrease.
7 CONCLUSION
In this paper crashworthiness of c-section s-rail of jeep chassis is determined. Five different materials used
for s-rail to compare energy absorption of each material via steel. Results showed that St-Mn S-rail has
great energy absorption and also it has suitable weight via steel model.
8 REFERENCES
1. Fridrich, H., Schumann, S., Research for a new age of magnesium in the automotive industry, Journal of
Material Processing Technology, vol. 117, 276-281, 2001.
2. Kim, H. New extruded multi-cell aluminum profile for maximum crash energy absorption and weight
efficiency, Thin Walled Structures, vol. 40, 311-327, 2002.
3. Abramowitz, W., Thin-walled structures as impact energy absorbers, Thin Walled Structures, vol. 41,
91-107, 2003.
4. Kim, H., Wierzbikci, T., Closed-form solution for crushing response of three- dimensional thin-walled s
frames with rectangular cross sections , International Journal of Impact Engineering, vol. 30, 87-112 ,
2004.
5. Shakeri, M., Darvizeh, A., Impact Mechanics, vol. 2, Gilan University Pub., 2000.
Figure 1. Physical model of impact striker with cylindrical shell
Figure 2. Element geometry of shell 163
p
L/2
Figure 3. Symmetric beam under impact loading
Figure 4. C-section dimension
Figure 5. S-rail mesh of Steel, Aluminum, Magnesium
Figure 6. S-rail mesh of Steel-Aluminum, Steel-Magnesium
250
ENERGY ABSORPTION
200 St Al Mn St-Al St-Mn
Mn St-Al
Al
150 St Absorbed Energy by
Analytical Method
Absorbed Energy by
100 Numerical Method
50
0
0 2 4 6
MATERIAL
Figure 7. Absorbed energy for St, Al, Mn, St-Al, At-Mn at m=4 kg, v=10 m/s
6000
ENERGY ABSORPTION
5000 St Al Mn St-Al St-Mn
Mn St-Al
Al
4000 St Absorbed Energy by
Analytical Method
3000
Absorded Energy by
Numerical Method
2000
1000
0
0 2 4 6
MATERIAL
Figure 8. Absorbed energy for St, Al, Mn, St-Al, St-Mn at m=4 kg , v=50 m/s
35000
St Al Mn St-Al St-Mn
30000
ENERGY ABSORPTION
Mn St-Al
Al
25000 St
Anergy Absorbed by
20000 Analytical Method
15000 Absorbed Energy by
Numerical Method
10000
5000
0
0 2 4 6
MATERIAL
Figure 9. Absorbed energy for St, Al, Mn, St-Al, St-Mn at m=4 kg , v=125 m/s
600
ENERGY ABSORPTION
500 St Al Mn St-Al St-Mn
St-Mn
Mn St-Al
400 Al
St Absorbed Energy by
Analytical Method
300
Absorbed Energy by
Numerical Method
200
100
0
0 2 4 6
MATERIAL
Figure 10. Absorbed energy for St, Al, Mn, St-Al, St-Mn at m=10 kg , v=10 m/s
14000
St Al Mn St-Al St-Mn
12000 St-Al
ENERGY ABSORPTION
Mn
Al
10000
St
Absorbed Energy by
8000 Analytical Method
6000 Absorbed Energy by
Numerical Method
4000
2000
0
0 2 4 6
MATERIAL
Figure 11. Absorbed energy for St, Al, Mn, St-Al, St-Mn at m=10 kg , v=50 m/s
90000
80000 St Al Mn St-Al St-Mn
ENERGY ABSORPTION Mn St-Al
70000
Al
60000 St
Absorbed Ebergy by
50000 Analytical Method
40000 Absorbed Energy by
Numerical Method
30000
20000
10000
0
0 2 4 6
MATERIAL
Figure 12. Absorbed energy for St, Al, Mn, St-Al, St-Mn at m=10 kg , v=125 m/s
Table 1. Properties of St., Al., Mn.
Material
Mn. Al. St.
Properties
Module of Elasticity (Pa.)
44.8E9 70E9 200E9
Yield Strength (Pa) 250E6 150E6 300E6
Hardening Strain Strength (Pa) 620E6 542E6 723E6
Density (Kg/m3) 1740 8700 2700
Table 2. properties of s-rails rather each other
Material StMn St-Al Mn Al St
Mass 569.15E-3 644.25E-3 218.37E-3 338.85E-3 1090.85E-3
Weight Reduction Percent 48% 41% 80% 69% ----
via Steel S-rail
Enhance Crashworthiness %293 %211 %200 %100 ----
Percent via Steel S-rail
