Static stress analysis and displacement of a tricycle rear

Leonardo Electronic Journal of Practices and Technologies

ISSN 1583-1078

Issue 33, July-December 2018

p. 139-158

139

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Engineering, Environment

Static stress analysis and displacement of a tricycle rear shock absorber

using finite element analysis

Temitope Olumide OLUGBADE 1*, Tiamiyu Ishola MOHAMMED 2, Oluwole Timothy

OJO1

1 Department of Industrial and Production Engineering, Federal University of Technology,

PMB 704, Akure, Ondo State, Nigeria

2Department of Mechanical Engineering, Federal University of Technology, PMB 704, Akure,

Ondo State, Nigeria

E-mails: [email protected]*, [email protected], [email protected]

*Corresponding Author, Phone: +2348068859326

Received: August 14, 2018 / Accepted: November 19, 2018 / Published: December 30, 2018

Abstract

The static stress analysis and displacement of a tricycle rear shock absorber using finite

element analysis (FEA) were carried out. The design of spring in the suspension system

was also studied. A physical model (pressure model and flow model) was adopted and

implemented for the modelling of the tricycle shock absorber. The pressure model

determines the internal pressures while flow model calculates the oil flow between the

tricycle chambers. Static stress analysis and displacements were performed by varying

materials for suspension spring and considering the tricycle weight at a loading capacity

of 1500 kg as well as when the loading capacity was exceeded by 200 kg. The analysis

was done to validate the strength and determine the best spring material for this

application. A comparison was made between the existing spring material Model and

other available spring materials. The results showed that the spring made of Inconel X-

750 has the least stress value when compared to other spring materials. This makes it a

better material in terms of load bearing capability. However, the material retained its

position as the most considerable material for making springs when the loading capacity

of the tricycle was exceeded and when there is unexpected overloading.

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Static stress analysis and displacement of a tricycle rear shock absorber using finite element analysis

Temitope Olumide OLUGBADE, Tiamiyu Ishola MOHAMMED, Oluwole Timothy OJO

140

Keywords

Static stress analysis; Finite element analysis; Shock absorber; Tricycle

Introduction

In vehicle dynamics, shock absorbers are part of the suspension system and the

importance of suspension cannot be overemphasized. It is needed to guarantee good handling,

braking, and comfort. Due to its complexity, it is sometimes challenging to design and model a

shock absorber of a suspension. It is therefore important to consider some factors while

designing for shock absorber, which includes geometry, strength, durability, and functionality.

A shock absorber is a mechanical assembly which is majorly used to support the weight, absorb

road shock and maintain tire contact as well as the proper wheel to chassis relationship in

automotive industries and structure analysis [1-2]. It does not only smooth out or damp shock

impulse but also absorb and dissipate the impact kinetic energy in such a way that accelerations

imposed upon the airframe are reduced to a tolerable rate [3]. Major problems associated with

tricycle operation are low ride quality, discomfort when over rough ground and unnecessary

disturbances. Also, the spring is compressed too quickly most times when a tricycle is traveling

on a level road and the wheels strike a bump. These problems can be resolved by designing a

good shock absorber for the tricycle using finite element analysis (FEA). This was

accomplished by designing a shock absorber using FEA which will, in turn, control the spring

and suspension movement.

Nowadays, several methods are available to model suspension system in a tricycle. The

applicability of these methods, discrete or diffuse depends on how they account for the supposed

discontinuity. To model a shock absorber, node splitting, cohesive surfaces, hybrid discrete and

finite element analysis are the common techniques using discrete methods [4-8]. Finite element

analysis (FEA) has been considered as an effective tool in shock absorber design to reduce the

error caused by the simplification of equations [9]. It has been presented to solve many

problems and equations numerically, for examples, modelling for chloride binding in mesoscale

concrete [10], phase-field solution for modelling brittle fracture [11], dynamics of flexible

beams [12], modelling hybrid all terrain trike [13], solid-shell formulation [14], determining

the reference geometry [15] and modelling helical compression spring for vehicle automotive

front suspension [16].


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Recently, studies on shock absorber and the suspension system have been a subject of

investigation. It has been established that without suspension, the tires could lose contact with

the road, traction would be lost, the ride would be uncomfortable, and chassis would as well be

subjected to damaging shock loads (9, 17-19). Finite element analysis (FEA) tools and

analytical solutions were used to compare the different stress and deflection values in shock

absorber components. Świtoński et al. [20] studied and analysed stiffness and damping of shock

absorber system. The results emphasized that the stiffness and damping value for shock

absorber is strongly related to the capacity of the shock absorber that was considered. Some

other factors such as damping force, control energy, and time constant are also important when

designing for shock absorber [21-23]. These factors and others like material selection and

strength, impact energy, toughness and durability are essential when designing for engineering

components [36-42].

Despite the various work done, few or little work has been done on the static stress

analysis and displacement of suspension spring of a tricycle. The comparison of different spring

materials that can be used for the design and analysis of the suspension spring of a tricycle has

also not been properly investigated.

In the present work, static stress analysis and displacement of a tricycle rear shock

absorber using finite element analysis (FEA) was carried out by varying coil springs made of

different materials. Firstly, a shock absorber used in the rear of a tricycle was designed and a

3D model was created. In addition, a comparison was made between the current spring material

(Monel K-500) and four other common spring materials to determine the best for making

suspension springs in tricycle shock absorber. The physical damper model is adopted for the

pressure model and flow model of the tricycle.

Materials and methods

Design calculations for the suspension spring shock absorber

The suspension spring shock absorber comprises of coil spring (helical), damper, piston

and fluid (oil). The analytical calculation for the considered suspension assembly was

performed using the basic design calculations and the same was compared with the ANSYS

results. Figure 1 illustrates the working algorithms of the designed tricycle rear shock absorber.



142

Figure 1. Working algorithm of the designed tricycle rear shock absorber.

In Figure 1, the working algorithm of the designed tricycle rear shock absorber include

the materials selections, design of shock absorber parts, design models, analysis and

calculations, and validation of models. The design of the coil-over helical spring was done using

the following vehicle data and information. Wet weight of tricycle (W) is 1200 kg (weight

include oil, fuel etc.). Loading capacity of tricycle is 1500 kg (weight includes added masses

such as persons). The rear axle bears the 63% of total weight (i.e.945 kg with load and 756 kg

without load) while front axle bears the remaining 37%.

Using the above vehicle data, the force on rear axle with and without load was obtained

to be 9450N and 7560 N respectively. The tricycle has two rear shock absorbers. With load, the

force exerted on each rear shock absorber was 4725 N while it was 3870 N without load. The

vertical force (with load) was 4725 N and the vertical displacement of the tire ground contact

with respect to chassis (with load) was 220 mm. By calculation, the ride rate of the tricycle with

load (vertical force per unit vertical displacement of the tire ground contact with respect to

chassis) was obtained to be 21.47 Hz. The ride rate of the tricycle with and without load are

21.47 Hz and 17.18 Hz respectively and the difference in the ride rate with and without load is

Comparison of Analytical and FEA results

Materials Selection and Considerations

Design of Shock Absorber Parts

Design Models and Analysis

Design Calculations

Static Stress Analysis and Displacement

Validation of Models


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4.29 Hz. This implies that the rate at which tricycle operates and moves (when fully loaded) is

more convenient and comfortable to users compared to the tricycle without load, which agrees

with the previous findings [19, 24-25].

Design considerations for the suspension spring (Helical)

In the present study, proper design of compression springs was taken into consideration

which requires the knowledge of both the potential and the limitations of available materials

together with simple formulae. The design of a coil spring involves the following basic

considerations: space into which the spring must fit and operate, working forces and deflections,

accuracy, reliability, tolerances, ride height, environmental conditions such as temperature, cost

and quality. These factors were used to select a material and suitable values for the wire size,

the number of turns, the coil diameter and the free length, type of ends and the spring rate which

is needed to meet the working force deflection requirements. The primary design constraints

are that the wire size should be commercially available and that the stress at the solid length be

no longer greater than the torsional yield strength.

The spring rate was calculated using the primary features which include the inside

diameter, wire diameter, coil mean diameter and number of active coils. The implication of

spring rate is that the greater the rate, the stiffer the spring and the more pounds of load it takes

to compress the spring one inch, Eq. [1], [17].

K = G × (d)4

8 × Na × (D)3 (1)

Where: K - spring rate, G - modulus of rigidity, d - wire diameter, D - coil mean diameter, Na

- number of active coils.

Evident from Eq. (1), suspension spring dimension including the wire diameter, mean

coil diameter, and the number of active coils is the major factors affecting the spring rate of a

steel coil. In the design analysis, value for modulus of rigidity was 2.124E+5 MPa, mean

diameter of a coil (D) was 80 mm, total no of coils (C) was 10, height (h) was 220 mm, diameter

of the wire (d) was 10 mm and the outer diameter of spring coil (D) was 90 mm, which was

obtained by the addition of inner and outer diameter of the spring coil. The axial load exerted

on the spring using the data in the design analysis was obtained to be 4725 N. The model of the

shock absorber assembly comprises the bottom part, top part and coil spring.



144

The physical damper model for the tricycle

The physical damper model adopted [26] was used for the modelling and analysis of the

tricycle rear shock absorber. The damper model was split into pressure model and flow model.

The pressure model predicts the internal chamber pressures while the flow model determines

the oil flow (Q) between the chambers in function of the pressure drop ∆p through a set of static

equations. From the rebound and compression chamber pressures, friction and bumper force,

the damper force is obtained, Eq. [2].

F = (Apt − Arod)Preb − AptPcom + Friction + Fbumper (2)

Where: F- damper force, Apt – area of pressure tube, Arod – area of damper rod, Preb – rebound

pressure, Pcom – compression chamber pressure, Fbumper - bumber force

Pressure model

Through a set of differential equations, the pressure model determines the dynamic

features of the damper. At low frequencies, the set of differential equations are related to the

adiabatic compression of the gas present in the reserve tube. It is important to note that some

undesirable effects such as the mixture of gas and oil in the pressure tube [27] can directly affect

the value of the bulk compressibility. The presence of such effects can greatly affect the damper

efficiency due to low bulk modulus. Double-tube and mono-tube design are considered under

the pressure model. This is because the difference in modelling of both types is most relevant

to pressure model. For double-tube design, the set of differential equations which can predict

the built-up of pressure in the pressure tube are presented in Eq. [3-4].

Preb =(x(Apt−Arod)−Qpv)(1−∝Preb)

(Lpt−x−x0)(Apt−Arod)α (3)

Pcom =(xApt+Qbv−Qpv)(1−∝Pcom)

(x+x0)Aptα (4)

Where: Ṗreb – rebound pressure (differentiation), Ṗcom – compression pressure (differentiation),

Qpv – flow rate of piston valve, Lpt – length of pressure tube, α – compressibility (Pa-1), x -

displacement (m), ẋ - differentiation of x, x0 – initial displacement, bv – base valve, pv – piston

valve


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For the reserve tube, the compressibility of the oil is infinitesimal compared to the

present gas. Hence, the reserve tube can be predicted from a polytrophic compression or

expansion, during the compression and rebound stroke, Eq. [5].

Prt = Prt,0 (Vrt,gas,0

Vrt,gas,0+ArodX)

γ

(5)

Where: Prt - pressure of reserve tube, Prt.0 - pressure of reserve tube, at original point, Vrt.gas.0 –

volume of reserve tube, gas at original point, x-displacement (m), γ- polytropic exponent.

For mono-tube design, only one tube is present and the change of volume inside the

damper body is compensated by a volume of gas at high pressure. In the rebound chamber, the

pressure remains the same while the pressure in the compression chamber is determined by the

compressed gas, Eq. [6-7].

Preb =(x(Apt−Arod)−Qpv)(1−∝Preb)

(Lpt−x−x0)(Apt−Arod)α (6)

Pcom = Pcom,0 (Vcom,gas,0

Vcom,gas,0+ArodX)

γ

(7)

Where: Pcom.0 – compression pressure, at original point, Vcom.gas.0 – compression volume, at

original point.

Flow model

The flow model shows the relationship between the flow rates through the valve

assemblies and the pressure drops. Pressure flow and intake flow are the two major models

under flow model. The pressure flow is responsible for the build-up of pressure drop across the

piston while the intake flow does not build up any important pressure drop across the valve

assembly, Eq. [8].

∆p = ∑ Bimi=1 Qri with ri ∈ R (8)

Where: Δp -pressure drop, Bi – global restriction coefficient, Qri – flow rate restriction

coefficient.

The series is truncated at two terms (m=2) with r1 = 1 and r2 mostly lies between 1 and

2. From literatures [28-29] r2 is usually fixed as 2 and calculate the coefficient B2, Eq. [9].

B2 =ρ

2(CDAV)2 (9)

Where: B2 - coefficient, ρ – oil density (kg/m3), CD – discharge coefficient, AV – valve area.



146

The discharge of coefficient CD is usually a function of the Reynolds number, the

Cauchy number, the acceleration number and the thickness to length ratio of the restriction [17].

Using B2 = 1.75, Reybrouck [30] argues that, Eq. [10].

∆p = KleakV1

4⁄ Qleak

74⁄

(10)

Where: Kleak – orifice stiffness, V1/4 – volume (m3), Qleak7/4 – orifice flow rate.

Considering the blow-off condition, Eq. [11].

∆Pblow−off ≥ ∆P0 (11)

Where: ΔPblow-off – blow-off pressure drop, ΔP0 – specific pressure developed

Blow-off valve can be modelled using Eq. [12]:

KspringQblow−off = (∆Pblow−off − ∆P0)√∆Pblow−off (12)

Where: Kspring – stiffness of blow-off spring, Qblow-off – blow-off flow rate

Based on literatures [17, 29, 31-33], Kspring and ∆Po can be obtained with Eq. [13, 14].

Kspring =Kspring

CDПdvAv√

ρ

2 (13)

∆Po =Fpreload

Av (14)

Where: CD – discharge coefficient, П – constant (3.142), dv – valve diameter, Av – valve area

The total valve feature is determined by taking into consideration, Eq. (15-17).

∆Ptot = ∆Pport + ∆Pparallel (15)

∆Pparallel = ∆Pblow−off = ∆Pleak (16)

Qtot = Qleak + Qblow−off (17)

Where: ΔPtotal – total pressure drop, ΔPport – pressure drop in port channel, ΔPparallel – pressure

drop in parallel, ΔPleak – pressure drop in orifice, Qtot - total flow rate, Qleak - orifice flow rate,

Qblow-off - blow off flow rate.

In series, the pressure drop across two elements is the addition of the pressure drop

across each element (Eq. [15]). The pressure drop in parallel, across two elements is the same

to the drops across each element (Eq. (16)) while the total flow of two valves in parallel is equal

to the sum of the flows across individual elements (Eq. (17)).


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Finite element approach (FEA)

The model was validated by comparing with the results obtained from Pinjarla and

Lakshmana [3] and Sudarshan et. al [19]. The parameters used for the validation (compares

between the developed model and the published results) are the loading capacity, force exerted,

analytical stress, boundary conditions and material properties. The percentage error between

the analytical stress obtained from this work compared with the previous result [3, 19] is 2.11

% while the percentage error in terms of loading capacity is 1.98 %, which is similar with the

previous work [19, 24]. FEA was used to predict the behaviour of a model in response to loads

that it will be subjected to. FEA allows for model development to be carried out at low cost and

can result in the removal unnecessary mass should it be determined that the design would still

retain enough strength properties without it.

Results and Discussion

Static stress analysis and displacement of selected wire materials

The analytical and FEA results obtained from the static stress analysis and

displacements of selected shock absorber wire material are presented in Tables 1-4.

Table 1. Static stress analysis and displacements of selected shock absorber wire material

No Material Young’s modulus

(E) MPa

Density

(Kg/m3)

Force

(N)

1 Nickel Base Alloy (Monel K500) 1.79×109 8440 4725

2 High-carbon Steel (ASTM A 228) 2.1×109 7850 4725

3 Alloy steel (ASTM A401) 2×109 7850 4725

4 Stainless Steel (AISI 302/304) 1.93×109 7860 4725

5 High temperature alloy (Inconel X-750) 2.124×109 8280 4725

Table 2. Summary of FEA result at tricycle loading capacity (4725N) for different shock

absorber wire materials

No Wire

material

Minimum

deflection (mm)

Maximum

deflection (mm)

Maximum

stress (MPa)

Density

(Kg/m3)

1 Monel K500 0.0064707 0.010246 37.213 8440

2 ASTM A 228 0.0066108 0.010461 37.761 7850

3 ASTM A401 0.0067469 0.010678 38.534 7850

4 AISI 302/304 0.0068492 0.010841 39.130 7860

5 Inconel X-750 0.0064742 0.010244 36.978 8280



148

Table 3. Summary of FEA result at tricycle overloaded capacity (5000N)

No Wire

material

Minimum

deflection (mm)

Maximum

deflection (mm)

Maximum

stress (MPa)

Density

(Kg/m3)

1 Monel K500 0.008932 0.013518 43.434 8440

2 ASTM A 228 0.009174 0.013761 44.217 7850

3 ASTM A401 0.009337 0.014006 45.000 7850

4 AISI 302/304 0.009499 0.014250 45.782 7860

5 Inconel X-750 0.009012 0.013498 43.043 8280

Table 4. Comparison of numerical (FEA) and theoretical values of maximum deflection

(loading capacity of 4725N)

No Method

loading (4725 N)

Monel

K500

ASTM

A228

ASTM

A401

AISI

302/304

Inconel

X-750

1 Numerical (FEA) 0.010246 0.010461 0.010678 0.010841 0.010244

2 Theoretical 0.015394 0.013122 0.013778 0.014277 0.012973

Loading (5000 N)

1 Numerical (FEA) 0.013518 0.013761 0.014006 0.014250 0.013498

2 Theoretical 0.0162905 0.013885 0.014579 0.015108 0.013728

As shown in Tables 1-4, the selected shock absorber wire materials are nickel base alloy

(Monel K500), high-carbon steel (ASTM A228), alloy steel (ASTM A401), stainless steel

(AISI 302/304) and high temperature alloy (Inconel X-750) (Table 1). The different stress and

deflection values in shock absorber wire material was obtained using ANSYS FEA tool. The

results obtained at loading capacity (4725 N) for different shock absorber wire materials are

summarized in the Table 2. The results obtained when the loading capacity was exceeded for

different shock absorber wire materials were also summarized in Table 3. The absorber

geometries such as the thickness of spring have influence on the deflection in stiffness and

damping of shock absorber system. In addition, the stiffness and damping value for shock

absorber are strongly related to the capacity of the shock absorber. The geometric study was

considered putting into consideration the damping force, control energy and time constant.

Moreover, Table 4 shows the results obtained when the loading capacity of the tricycle

was exceeded. This is required for load bearing structural members to determine their behaviour

when there is unexpected overloading. From the results obtained, Inconel X-750 retained its

position as the most considerable material for making springs.


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(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)



150

(j)

Figure 2. The magnitude of maximum deflection in the spring and the equivalent stress in the

shock absorber (a) and (b) nickel base alloy (Monel K500), (c) and (d) high carbon steel

(ASTM A228), (e) and (f) alloy steel ASTM A401, (g) and (h) stainless steel (AISI 302/304),

(i) and (j) high temperature alloy (Inconel X-750).

Figure 2 a-j shows the magnitude of maximum deflection in the spring and the

equivalent stress in the shock absorber of the five (5) selected shock absorber wire materials.

For nickel base alloy (Monel K500), the magnitude of maximum deflection in the spring is

0.010246 mm, as shown in Figure 2a and the maximum shear stress in the shock absorber is

37.213MPa, as shown in Figure 2b. Also, from Figure 2b, the values of deflection in Monel K-

500 wire under static load of 4725 N force are obtained within the range of 0.0064707 mm and

0.010246 mm.

The magnitude of maximum deformation in the spring for high carbon steel (ASTM

A228) is as shown in Figure 2c while Figure 2d shows the maximum shear stress in the shock

absorber. The magnitude of maximum deformation in the spring is 0.010461 mm and the

maximum shear stress in the shock absorber is 37.761 MPa. Within the range of 0.0066108 mm

and 0.010461 mm, from Figure 2d, the values of deflection in ASTM A228 wire under static

load of 4725 N force are obtained within the range of 0.0066108 mm and 0.010461 mm. Figure

2e shows the magnitude of maximum deformation in the spring for alloy steel ASTM A401.

Figure 2f shows the maximum shear stress in the shock absorber. The magnitude of maximum

deformation in the spring is 0.010678 mm and the maximum shear stress in the shock absorber

is 38.534 MPa. In Figure 2f, the values of deformation in ASTM A401 wire under static load

of 4725N force are obtained within the range of 0.0067469 mm and 0.010678 mm.

In Figure 2g, the magnitude of maximum deformation in the spring for stainless steel

(AISI 302/304) is illustrated. Figure 2h shows the maximum shear stress in the shock absorber.


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The magnitude of maximum deformation in the spring is obtained to be 0.010841 mm and the

maximum shear stress in the shock absorber is given as 39.13 Mpa. Figure 2h also showed that

the values of deformation in AISI 302/304 wire under static load of 4725 N force are obtained

within the range of 0.0068492 and 0.010841 mm. The magnitude of maximum deformation in

the spring for high temperature alloy (Inconel X-750) is illustrated in Figure 2i while Figure 2j

shows the maximum shear stress in the shock absorber. The magnitude of maximum

deformation in the spring is 0.0064742 mm and the maximum shear stress in the shock absorber

is 36.978 MPa. The values of deformation in Inconel X-750 wire under static load of 4725N

force are obtained within the range of 0.0064742 mm and 0.010244 mm, as evident in Figure

2j.

From Table 3, it can be deduced that the shock absorber made of spring material Inconel

X-750 has the least stress value of 36.978 MPa which makes it a better material in terms of load

bearing capability, which agrees with the previous results [25, 34]. In terms of deflection or

deformation, Monel K-500 has the least deformation with value of 0.0064707mm. This

compared with deformation in Inconel X-750 with value of 0.0064742mm is very insignificant

and not noticeable. Though, materials with larger deflection value has tendency to buckle than

materials with less deflection value, but Inconel X-750 has less deflection value compared to

the rest of the materials, as established from previous studies [35].

Weight is also an important aspect of the product development, and every attempt must

be made to adhere to the specified weight of the shock absorber. The springs of the various

materials are of equal volume with different densities. Inconel X-750 has a density which is

lesser than that of Monel K-500 translating to the fact that it is lighter. Compared with the

previous reports [17, 28], the shock absorber design is safe because the equivalent stress

obtained with the entire materials is lesser than their respective yield strength. Inconel Alloy

has higher resistance to deformation and failure because it has the least stress value than Monel

K-500; hence, it can be used as an alternative material for making helical springs in tricycle

shock absorber, similar conclusion was made [24-25].

Analytical approach

To validate the above result, theoretical calculation is being carried out below for Monel

K500, ASTM A 228, ASTM A401, AISI 302/304, Inconel X-750. Consequently, for all the



152

spring materials, the spring constant, maximum deflection (for loading capacity of 4725 N and

overloaded capacity 5000 N), spring index and maximum shear stress are calculated using Eq.

(18-22):

k = G × (d)4

8 × n× (D)3 (18)

δ = F

k (19)

C = D

d (20)

W =4C−1

4C−4+

0.615

C (21)

τ = 8 ×W× D×F

πd3 (22)

Where: G - modulus of rigidity, d - wire diameter, D - mean coil diameter, n - no of active coils,

δ - maximum deflection, F - maximum force, k – spring constant, C - spring index, τ - maximum

shear stress, W - wahl correction factor.

The maximum deflection and stress values obtained from the analytical approach are

summarized and compared with the numerical values as shown in Table 4.

Comparison of numerical (FEA) and theoretical values of maximum deflection

Figure 3 represents the numerical results of maximum deflection at loading capacity of

4725 N and overloaded capacity of 5000N for different suspension spring materials while the

maximum shear stress numerical results for various spring materials at different loading

capacity are shown in Figure 4.

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

Monel K500 ASTM A228 ASTM A401 AISI 302 INCONEL X-750

Ma

xim

um

de

flectio

n (

mm

)

Loading capacity - 4725N


Figure 3. ANSYS results of maximum

deflection at loading capacity of 4725 N and

overloaded capacity of 5000 N for different

suspension spring materials

37.213 37.761 38.534 39.1336.978

43.434 44.217 45 45.78243.043

37.213 37.761 38.534 39.1336.978

43.434 44.217 45 45.78243.043

0

10

20

30

40

50

60


Maxim

um

str

ess (

MP

a)



Figure 4. ANSYS results of maximum stress

for different suspension spring materials at

loading capacity of 4725 N and overloaded

capacity of 5000 N


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In both the numerical and theoretical analysis, AISI302/304 (among the suspension

spring materials) has the highest maximum deflection and stress at loading capacity of 4725 N

and 5000 N. At 4725 N, the maximum deflection for numerical and theoretical analysis are

0.010841 mm and 0.014277 mm respectively (Figure 3) while it is 0.014250 mm and 0.015108

mm for numerical and theoretical analysis respectively, at 5000 N (Figure 4).

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09


Maxim

um

deflection (

mm

)

Numerical (FEA) deflection

Theoretical deflection

Figure 5. Comparison of numerical (FEA)

and theoretical values of maximum

deflection for different suspension spring

materials at loading capacity of 4725 N

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

0.022


Maxim

um

deflection (

mm

)

Numerical (FEA) deflection

Theoretical deflection

Figure 6. Comparison of numerical (FEA)

and theoretical values of maximum

deflection for different suspension spring

materials at loading capacity of 5000N

The results obtained from numerical (FEA) and theoretical analysis or both maximum

deflection and maximum shear stress are compared, as shown in Figure 5 and Figure 6. The

comparison was done when the loading capacity is 4725 N and when there is overloaded

capacity (5000N) for the different suspension spring materials.

As evident in Figure 5 and Figure 6, for all the suspension spring materials except Monel

K500, it is observed that the numerical and theoretical values for both maximum deflection and

shear stress are close when the loading capacity is 4725 N and 5000 N. The significant

difference between the numerical and theoretical values of Monel K500 is a little bit more

compared to the differential values of the remaining four (4) suspension spring materials.

Conclusions

Statistical stress analysis of suspension spring of a tricycle was carried out to solve the

major problems associated with tricycle operation which include low ride quality, discomfort



154

when over rough ground, unnecessary disturbances and quick compression of springs. This was

done by designing a good shock absorber for the tricycle using finite element analysis (FEA),

which in turn control the spring and suspension movement. The essential points of this work

are as follows:

(1) The physical damper model which consist of pressure model and flow model, was adopted

for modelling the tricycle, to determine the internal pressure and calculate the oil flow

between the tricycle chambers. Static stress analysis of five (5) different suspension spring

materials was done. Two different analysis methods are implemented: the numerical

analysis using finite element method and theoretical analysis which was employed for

validation purpose.

(2) The analysed stress values are less than their respective yield stress values. This makes the

design distinct. By comparing the results for the five (5) materials, the spring made of

Inconel X-750 has the least stress value, deformation and a density of 8280 kg/m3 which is

lesser than that of Monel K-500. It can be concluded that Inconel X-750 is the best material

for making helical springs in a tricycle rear shock absorber because of its low deformation

value, less weight and cost. This conclusion was confirmed in line with the computations

for numerical examples that were studied using the developed model.

(3) The method of finite element analysis was employed to evaluate the performance of

different coil spring materials, to determine the material with the least deformation under a

given condition (loading).

In future work, the combination of experimental, numerical and theoretical approach

will be adopted for the structural and modal analysis of shock absorber. In addition, finite-

element formulation based on interpolation of strain measures will be developed and dynamics

of flexible spring following the same approach.

Acknowledgements

Special thanks to Fashade Olalekan for his assistance during this research. This research did

not receive any specific grant from funding agencies in the public, commercial or profit sectors.


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155

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Documents

Static stress analysis and displacement of a tricycle rear