(VSS) and its Effect on Global Warming

Available online at www.sciencedirect.com

ScienceDirect Procedia Engineering 159 (2016) 124 – 132

Humanitarian Technology: Science, Systems and Global Impact 2016, HumTech2016, 7-9 June 2016, Massachusetts, USA

Design and simulation of fatigue analysis for a vehicle suspension system (VSS) and its effect on global warming Christianah O. Ijagbemia,*, Bankole I. Oladapob, Harold M. Campbella, Christopher O. Ijagbemi b

a Department of Industrial Engineering, Tshwane University of Technology, Pretoria, South Africa Department of Mechanical & Mechatronics Engineering, Afe Babalola University, Ado-Ekiti, Nigeria d Department of Estate Management, Federal Polytechnic, Ado-Ekiti, Nigeria

Abstract Research shows that for every gallon of gasoline burnt, 12.7kg of CO2 is released. Fuel economy improvement is almost linear with a reduction in weight of a car. Therefore, reducing vehicle weight results in less fuel consumption and a decrease in CO 2 emission which in turn has an effect on global warming. Car manufacturers are facing increasingly stringent CO2 emission standard. In this project, an investigation was carried out on vehicle suspension system (VSS) by employing Finite Element Analysis (FEA) to analyze the fatigue life, von misses stress, factor of safety and stability of the suspension system and how the weight and size can be reduced. Solidworks14 ® was employed to analyze different materials used in the design and development of VSS; comparison amongst the various materials used was carried out to inform that there can be reduction in the size and weight of the four suspension system by using Titanium Ti-13V-11Cr-3Al Treated, which will drastically reduce the weight of the car and give better result of strength and durability, ultimately reducing CO 2 emission and its negative effect on the climate. This innovative design can be introduced as a reference for the automotive industry. © 2016 The © The Authors. Authors.Published PublishedbybyElsevier ElsevierB.V. B.V. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the Organizing Committee of HumTech2016 (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the Organizing Committee of HumTech2016 Keywords: Vehicle suspension system (VSS); finite element analysis (FEA); CO2 emission; fatigue life; solidworks14®; global warming

1. Introduction People talk about the performance of automobile, the power, speed, torque and acceleration of the vehicle, however, all the power produced by the engine is worthless if the car cannot be maximally control; the reason why automotive engineers focus their attention on the suspension system of a vehicle as soon as they have mastered the design of the engine [1,2,3]. Suspension system entails the tires, shock absorbers, springs and linkages that connect a vehicle to its wheels and allows relative motion between the system and the road [4]. Suspension system helps in the vehicle's braking system for safety, driving pleasure and keeping the passengers comfortable with a ride free of road noise, bumps, and vibrations [4,5,6]. If roads were perfectly smooth, suspension system would not be necessary for a vehicle, it is these irregularities that pose disturbance to the wheels. Bump and potholes on the road cause the wheel of a vehicle to move up and down, perpendicular to the surface the road. The magnitude of the force, depends on the wheel striking a small or giant bump [6-7]; this makes the car wheel experience a sudden vertical movement as it passes over the bumps. This paper, therefore, explore how car suspensions can be designed with low overall weight, low fuel consumption and still withstand fatigue during operation. The suspension system is made up of the spring and fluid damping system. The spring absorbs energy from an applied force, this energy is stored in the spring until the force is released, then, the spring will return to its original size, shape and position [8,9]. It is, therefore, essential for the vehicle suspension system to keep the wheel in contact with the road surface. The design, modeling and simulation of the front and rear suspension of a car are similar [9, 10, 11]. * Corresponding author. Tel.: +27 60 060 0816. E-mail address: [email protected], [email protected]

1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of HumTech2016

doi:10.1016/j.proeng.2016.08.135

Christianah O. Ijagbemi et al. / Procedia Engineering 159 (2016) 124 – 132

Apparently, four-wheel vehicles need suspension system for both the front and rear wheel suspension [8, 9], weight transfer during navigation, acceleration or braking is calculated per individual wheel and then compared with the static weights of the wheels [12, 13, 14]. Mitsubishi was the first to develop the semi-active electronically controlled suspension system in small cars; it was first used in 1987 in Gallant model. Delphi now produces shock absorbers that contain magneto-rheological fluid, which has the ability to change the viscosity electromagnetically, this gives variable control without changing valves, which is faster and effective [15, 16]. Vehicle’s size and weight have an important role to play in fuel consumption. Fuel economy is directly proportional to the weight of a vehicle. A 30% decrease in vehicle weight is approximately 30% decrease in fuel consumption. Assuming a Toyota Camry car weighs 1490kg and runs 50 miles per gallon (mpg), the same car would make 55mpg if the weight is 1330kg. Emission of Carbon dioxide (CO2) is a major concern globally because of its greenhouse effects which contribute to global warming. With studies confirming that CO2 emission is proportional to fuel consumption [9,10]; therefore, a reduction in vehicles fuel consumption will result in reduced CO2 emission which is the main objective of this work – designing a suspension system of reduced weight with solidworks14 and its analysis using Finite Element Method. Nomenclature cd Fd [M] [C] [K] {f(t)}

Constant slope of the curve Mass (or inertia) matrix Damping matrix Stiffness matrix n-dimensional force vector

2. Methodology The study is on modeling a suspension system and the analysis of its factor of safety, stresses involved and displacement under random loading conditions. CAD models of the suspension system of a vehicle were developed with a 3D modeling software [9, 10]. The fatigue and stress analysis of the models were obtained and compared using FEA with Solidworks14 Simulation Software to optimize for weight reduction. The weight of the designed suspension system was then compared to the weight of an existing VSS. 2.1. Problem Statement Coil spring in a suspension system supports the loading effect on the system. It is subjected to different influences of stress and fatigue. The four springs; one at each wheel of the vehicle, are subjected to road factors and driving drills. Therefore, it is of great necessity to check the stress, factor of safety and fatigue strength of spring and other parts of the suspension system in order to have improved and problem-free service life. The fatigue life of the suspension system is significantly affected by physical and chemical properties of the materials that make each component of the VSS. Failure of spring or any part of the suspension system can lead to an accident, which may injure the occupant and cause damage to the vehicle. This work analyzed the von misses stress, the factor of safety, percentage damage and the fatigue life of the suspension system of a car of about 7000 kg [18-20] as the average weight of a car. The intention is to have a weight-reduced durable car in the future, by the different automotive company. 3. Design and finite element analysis of suspension system assembly The static and finite element analysis of the suspension system assembly was performed on Solidworks Professional in the manner highlighted below: 1. the design calculation of the system VSS was carried out, 2. the modeling of a three-dimensional suspension system assembly which consist of the hub attached to the wheel, the upper and lower arms and the spring connector, 3. the selection of materials was done based on typical materials used for existing suspension systems and materials that are readily available with good machinability properties; the chemical and physical properties of the material and the geometry data. 4. the simulation of the model after meshing and the generation of the result on static stress analysis were carried out.

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Table 1. Properties of the Materials. Name

Cast Carbon Steel

Malleable Cast Iron

Titanium Ti-13V-11Cr-3Al Solution Treated

Zinc AG40A (Zn-4Al-0.4Mg; Zamak 3), Cast

Model type

Linear Elastic Isotropic




Default failure criterion

Max von Mises Stress



-

Yield strength (N/m2)

2.48168e+008

2.75742e+008

8.3e+008

2.85e+008

Tensile strength (N/m2)

4.82549e+008

4.13613e+008

9.9e+008

4.15e+008

Elastic modulus (N/m2)

2e+011

1.9e+011

9.9e+010

8.5e+010

Poisson's ratio

0.32

0.27

0.3

0.3

Mass density (kg/m3)

7800

7300

4820

6600

Shear modulus (N/m2)

.6e+010

8.6e+010

4.3e+010

-

Weight (N)

4.2082384

3.9384723

2.6004701

3.5608061

Thermal expansion coefficient (1/Kelvin)

1.2e-005

1.2e-005

9.67e-006

2.74e-005

3.1. Loading condition of the system Forces were applied on the VSS in both radial and axial directions of about 14 kN/m2 and 2 kN/m2 respectively. The axial force was kept constant and the radial force was varied through 14, 16, 18, 20 and 22 kN/m2 [19-20]. Different values of the factor of safety, von miss stress, damage percentage and life cycle were recorded and plotted in Fig. 1 and 2. At these various loadings, the edge of the VSS was fixed to the body of the car. The spring connector was a flat parallel compression and extension of normal stiffness value of 30 kN/m2 at a tangential value of zero. The spring thickness is calculated using Eqn. 1 and further by employing Eqn. 2 and 3. For spring stiffness .

Fd

c

d

(u2 u1 )

(1)

For spring

mu(t ) ku(t )

F (t )

[M ]û(t )` [C]û(t )` [ K ]û(t )`

(2)

^ f (t )`

(3)

3.2. Stress calculation It can be observed that von misses stress (VMS) has no direction. It is defined by magnitude with units. It can be used for failure criteria to evaluate ductile materials. VMS is calculated from the components stress using Eqn. 4 and 5:

VON

>

@

1 2 2 2 2 2 2 ½ ® SX SY SX SZ SY SZ 3 TXY TXZ TYZ ¾ ¿ ¯2

1

2

(4)

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from the other principal stresses, we have

VON

>

@

1 2 2 2 ½ ® P1 P 2 P1 P3 P 2 P3 ¾ ¿ ¯2

1

2

(5)

3.3. Calculation of failure criteria Maximum stress criterion which is denoted by Eqn.6-10 was equally evaluated.

§V V V F .I . Max¨ 1 , 2 , 12 ¨ X1 X 2 S 12 ©

· ¸ ¸ ¹

(6)

Tsai-Hill Failure criterion for brittle material

F .I .

V 12 X 12

V 1V 2 X 12

V 22 X 22

W 122 S122

(7)

Tsai-Wu Failure criterion for brittle material where stress σ2 < 0

F11

1 , F22 X X 1C T 1

1 , F6 X X 2C T 2

§ 1 1 · ¨¨ T C ¸¸, F66 © X 12 X 12 ¹

1 X u X 12C T 12

(8)

4. Results and discussions In the design of VSS, the total weight of carbon cast steel is 4.2N, having a yield strength of 2.482e+008N/m2, shear modulus of 8.6e+010N/m2, thermal expansibility of 12e-005 1/Kelvin, mass density of 7800kg/m3, elastic modulus of 2e+011N/m2 and a tensile strength of 2.48168e+008N/m2 according to Table 1. There are five fixed joints which are pinned down to the car body. A radial and axial forces of 15 kN/m2 and 2 kN/m2 respectively were applied on the hub of the VSS which represents the reaction of the wheel; the force and the reaction of the weight of the vehicle in the VSS. The absorber system was made up of spring and damper.

Fig. 1. Minimum von miss stress of the materials.

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Fig. 2. Maximum von miss stress of the materials.

Fig. 3. Minimum factor of safety of the materials.

A flat parallel spring of compressive and extensive type was adopted. It has a normal stiffness value of 30 kN/m2 and tangential angle of zero degree. Four materials: Cast Carbon Steel, Malleable Cast Iron, Titanium Ti-13V-11Cr-3Al Solution Treated and Zinc AG40A (Zn-4Al-0.4Mg; Zamak 3) Cast were analyzed. As reported by [2], the yield strengths for the four materials were below the standard VMS value. Varying weights were considered: 14, 16, 18, 20 and 22 kN/m2 in order to obtain the minimum VMS, maximum VMS and minimum FOS. The results obtained were presented in Figure 1, 2 and 3. The total life cycle was loaded on 1 million lives which are the maximum life span of any car, this was experimented using the different materials, results obtained are presented in Figure 4 and 5 which favored all the materials. Figure 6 shows the FOS at maximum von miss stress, only Titanium Ti-13V-11Cr-3Al Solution Treated has approximately one (1) as minimum FOS but others are between 0.2 and 0.3 which imply that the materials are not safe for use.


Cast Carbon Steel

Malleable Cast Iron


Zinc AG40A (Zn-4Al-0.4Mg; Zamak 3), Cast Fig. 4. VON mises stress plots.

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Malleable Cast Iron Cast Carbon Steel


Zinc AG40A (Zn-4Al-0.4Mg; Zamak 3), Cast Fig. 5. Fatigue total life.

The Fatigue strength was determined by applying different levels of cyclic stress to discrete check of materials used and the number of cycle failure was measured. The graphical representation of fatigue data points is the stress amplitude on the vertical axis against the number of cycles to failure on the horizontal axis. The four materials were tested in a series of decreasing stress levels until no failure occurs within a selected maximum number of cycles of 1 million. The simulation and experimental results showed that the mean stress VMS and FOS are important factors in the fatigue resistance of the four materials. This was also reported by [9, 17-22].


Cast Carbon Steel

Malleable Cast Iron


Zinc AG40A (Zn-4Al-0.4Mg; Zamak 3), Cast

Fig. 6. Factor of safety plot at max von mises stress for materials.

5. Conclusion The fatigue life and static stress analysis of a VSS adopting finite element analysis technique provided a reliable design that can be employed in VSS designs. This work presents a fatigue evaluation for VSS and based on the simulation obtained, it can be said that: x the present VSS that is made up of carbon alloy can be reduced to a lighter weight VSS with good durability and machinability; with an advantage of a low CO2 emission. x the FOS for carbon alloy at a suitable yield stress below VMS value is approximately 0.35 at the different loads considered, x Titanium Ti-13V-11Cr-3Al Solution Treated has an FOS of approximately 1 for the different loading conditions and still has a suitable yield strength, x Safety of the vehicle and passengers can be guaranteed by the use of Titanium Ti-13V-11Cr-3Al Solution Treated in VSS designs.

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