Materials Engineering: Journal Bearing Selection with AHP

This assignment provides a detailed solution to a problem involving the selection of appropriate materials for a journal bearing, considering various mechanical properties and performance criteria. The solution employs the Analytical Hierarchy Process (AHP) to determine the relative importance of criteria such as yield strength, fatigue strength, wear resistance, and cost. Different materials like Alloy Cast Iron, Stainless Steel, Zinc Alloy, Magnesium, and Thorium are evaluated based on their properties and AHP-derived weights. The assignment also discusses the design criteria for hydraulic dampers in automobile suspension systems, focusing on material properties like tensile strength, yield strength, and corrosion resistance, and suggests suitable materials such as high-speed steel, alloy steel, and carbon steel. The document further explores methods for material selection, including the limits on property method, and emphasizes the importance of considering material indices for optimal component performance. This assignment is available on Desklib, where students can find a wide array of study resources including past papers and solved assignments.

Question and Answer
1 | P a g e
Materials Engineering

Question and Answer
Contents
Solution 1.........................................................................................................................................3
Solution 1a)..................................................................................................................................3
Solution 1b).................................................................................................................................4
Solution 1c)..................................................................................................................................7
Solution 2.........................................................................................................................................7
Solution 2a...................................................................................................................................7
Solution 2b...................................................................................................................................9
Solution 2c.................................................................................................................................10
Solution 2d.................................................................................................................................10
References......................................................................................................................................11
2 | P a g e

Question and Answer
Solution 1
As per given in question we have to selectin the material for journal bearing, which will come
under the given mechanical parameter and part from the material given in the list. The given
requirement of the material describes that it should withstand reaction forces which means its
fatigue strength and yield strength is important parameter additionally, sliding movement which
means that it should have wear resistance of important parameter. The frictional losses can be
reduced by lubrication. The given criteria can be ranked as per the requirement of journal
bearing. For this purpose, we will opt for analytical hierarchy process. The reason for choosing
this method is its simple in analysing the different materials (Farag, 2014).
The probable candidate for journal bearing with their property as follows. We have selected 5
different material, which is names as Alloy Cast Iron, Stainless Steel, Zinc Alloy, Magnesium
AM100A-F, Cast, Thorium, Th. The various mechanical property is as follows.
Solution 1a)
Table 1-Material Property Data (sources - metweb)
YS Fs
Thermal C
(W/M-K)
Corrosio
n
Wear
R
hardnes
s Y' m Relative Cost
Alloy Cast Iron (ASTM
A536) 811
289.4
5 32.3 3 3 98 76
0.29807103
8
Stainless Steel 665 435 22.5 4 4 89 89
0.45560668
2
Zinc Alloy (UNS
Z15001) 277 60.1 109 5 4 42 83
0.73214407
1
Magnesium AM100A-F,
Cast 83 69 73 4 4 53 45 0.52134098
Thorium, Th 200 97 37.7 4 4 99 73.1 10
Based on the above material property data. Comparison of material.
YS Fs
Thermal C
(W/M-K) Corrosion Wear R hardness Y' m Relative Cost
Importan
ce
YS 1.00 7.00 3.00 2.00 2.00 5.00 4.00 7.50 8.00
Fs 0.14 1.00 0.50 0.50 0.50 0.50 0.50 0.50 7.00
Thermal
C (W/M-
K) 0.33 2.00 1.00 0.50 0.50 0.50 0.50 0.50 3.00
Corrossi
on 0.50 2.00 2.00 1.00 0.50 0.50 0.50 0.50 2.00
Wear R 0.50 2.00 2.00 2.00 1.00 0.50 0.50 0.50 2.00
hardness 0.20 2.00 2.00 2.00 2.00 1.00 0.50 0.50 5.00
Y' m 0.25 2.00 2.00 2.00 2.00 2.00 1.00 0.50 4.00
Relative
Cost 0.13 2.00 2.00 2.00 2.00 2.00 2.00 1.00 7.50
3 | P a g e

Question and Answer
Sum 3.06 20.00 14.50 12.00 10.50 12.00 9.50 11.50
Avera
ge
0.3413
48
0.044
78
0.063122
14
0.0837
61
0.100
13
0.1049
86
0.1240
24
0.137850
395
After normalising the above table
YS Fs
Thermal
C (W/M-
K) Corrossion
Wear
R hardness Y' m
Relative
Cost
Average
weight CM
YS
0.326
8 0.3500 0.2069 0.1667 0.1905 0.4167 0.4211 0.6522 0.3413 3.27 9.570468
Fs
0.046
7 0.0500 0.0345 0.0417 0.0476 0.0417 0.0526 0.0435 0.0448 0.40 8.943338
Thermal C
(W/M-K)
0.108
9 0.1000 0.0690 0.0417 0.0476 0.0417 0.0526 0.0435 0.0631 0.54 8.583982
Corrossion
0.163
4 0.1000 0.1379 0.0833 0.0476 0.0417 0.0526 0.0435 0.0838 0.70 8.401728
Wear R
0.163
4 0.1000 0.1379 0.1667 0.0952 0.0417 0.0526 0.0435 0.1001 0.84 8.364746
hardness
0.065
4 0.1000 0.1379 0.1667 0.1905 0.0833 0.0526 0.0435 0.1050 0.89 8.456155
Y' m
0.081
7 0.1000 0.1379 0.1667 0.1905 0.1667 0.1053 0.0435 0.1240 1.07 8.642195
Relative
Cost
0.043
6 0.1000 0.1379 0.1667 0.1905 0.1667 0.2105 0.0870 0.1379 1.22 8.886209
1.000
0 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 8.9351
The constancy index is calculated with the formula CI =λ−n/n−1 = 0.133579
And consistency ratio = CI/RI (where RI = 1.41 for 8 properties)
CR = 0.094 which is less than 0.1 therefore, the calculation is consistent and according to
this calculation Average weight is highest for yield strength. And yield strength is highest for
Alloy Cast Iron Alloy Cast Iron (ASTM A536). Therefore, Cast Iron Alloy Cast Iron (ASTM
A536) is the best alternate material for making journal bearing (Material Selection using CES
edupack, 2010).
Solution 1b)
For the calculation of relative importance for each criterion given, we take yield strength and
thermal conductivity equal and prime importance for journal bearing materials. Fatigue is
relative given as less importance as yields strength Corrosion and wear resistance is of moderate
importance because dust and open area can affect the journal bearing, after that hardness,
young’s modulus and cost is kept at the lower level of importance.
4 | P a g e

Question and Answer
Again, tabulating all the properties,
Properties Importance
YS 8.00
Fs 7.00
Thermal C (W/M-K) 8.00
Corrosion 6.00
Wear R 5.00
hardness 4.00
Y' m 3.00
Relative Cost 2.00
The pair wise comparison for above properties
YS Fs
Thermal C
(W/M-K)
Corrossi
on
Wear
R
hardnes
s Y' m
Relative
Cost
Import
ance
YS 1.00 7.00 8.00 6.00 5.00 4.00 3.00 2.00 8.00
Fs 0.14 1.00 0.50 0.50 0.50 0.50 0.50 0.50 7.00
Thermal C
(W/M-K) 0.13 2.00 1.00 0.50 0.50 0.50 0.50 0.50 8.00
Corrossion 0.17 2.00 2.00 1.00 0.50 0.50 0.50 0.50 6.00
Wear R 0.20 2.00 2.00 2.00 1.00 0.50 0.50 0.50 5.00
hardness 0.25 2.00 2.00 2.00 2.00 1.00 0.50 0.50 4.00
Y' m 0.33 2.00 2.00 2.00 2.00 2.00 1.00 0.50 3.00
Relative
Cost 0.50 2.00 2.00 2.00 2.00 2.00 2.00 1.00 2.00
Sum 2.72
20.0
0 19.50 16.00
13.5
0 11.00 8.50 6.00
Averag
e
0.34134
7609
0.04
478
0.0631
2214
0.083
761
0.10
013
0.104
986
0.124
024
0.13785
0395
The consistency measures are as follows
YS Fs
Therm
al C
(W/M-
K)
Corrossio
n
Wea
r R
hardnes
s
Y'
m
Relati
ve
Cost
Avera
ge
weight CM
5 | P a g e

Question and Answer
YS 0.3679
0.35
00 0.4103 0.3750
0.37
04 0.3636
0.35
29 0.3333 0.3654 3.23
9.4645
76
Fs 0.0526
0.05
00 0.0256 0.0313
0.03
70 0.0455
0.05
88 0.0833 0.0480 0.40
8.9433
38
Thermal C
(W/M-K) 0.0460
0.10
00 0.0513 0.0313
0.03
70 0.0455
0.05
88 0.0833 0.0566 0.47
7.4573
71
Corrossion 0.0613
0.10
00 0.1026 0.0625
0.03
70 0.0455
0.05
88 0.0833 0.0689 0.59
7.0433
01
Wear R 0.0736
0.10
00 0.1026 0.1250
0.07
41 0.0455
0.05
88 0.0833 0.0829 0.74
7.3420
28
hardness 0.0920
0.10
00 0.1026 0.1250
0.14
81 0.0909
0.05
88 0.0833 0.1001 0.90
8.6187
23
Y' m 0.1226
0.10
00 0.1026 0.1250
0.14
81 0.1818
0.11
76 0.0833 0.1226 1.10
8.8715
51
Relative
Cost 0.1840
0.10
00 0.1026 0.1250
0.14
81 0.1818
0.23
53 0.1667 0.1554 1.35
9.7941
55
1.0000
1.00
00 1.0000 1.0000
1.00
00 1.0000
1.00
00 1.0000 1.0000 8.7823
Average
weight CM
0.3654 3.23
9.46457
6
0.0480 0.40
8.94333
8
0.0566 0.47
7.45737
1
0.0689 0.59
7.04330
1
0.0829 0.74
7.34202
8
0.1001 0.90
8.61872
3
0.1226 1.10
8.87155
1
0.1554 1.35
9.79415
5
1.0000 8.7823
The average weight shows that the yield strength is of highest importance.
6 | P a g e

Question and Answer
Solution 1c)
As per the result obtained from AHP for give material,
Properties
Average
weight Material
YS 0.365434322 Aluminium based alloy
Relative Cost 0.15543246 Lead base alloy
Y' m 0.122644558 Copper alloy
hardness 0.100095304 Aluminium based alloy
Wear R 0.082854621 Copper based alloy
Corrosion 0.068879421 Tin Based
Thermal C (W/M-K) 0.056646577 Aluminium based alloy
Fs 0.048012736 Aluminium based alloy
The yield strength is of highest importance as per weight, the second and third important criteria
is Relative cost and Young’s modulus. Out of eight properties, four properties can be obtained
from aluminium based alloy, in which Yield strength which is of highest importance are falling
under this material category, therefore, aluminium based alloy is the best material for Journal
bearing (Creations, 2017).
Solution 2.
Solution 2a.
It is one of the most important part of engine system, most of the time it is a mechanical
assembly and integrated with the wheel of the automobile. The main purpose of this suspension
system in the automobile is to reduce the vertical movement of the car so that the traveller feel
comfort. It consists of wishbones, spring and shock absorber with damper. Basically, there are
two type of suspension system, the detail given above is for primary suspension system. The
secondary suspension system consists of seats of the traveller. Further this also be classified as
active and passive suspension system.
Passive suspension system:
The passive suspension system consists of fixed spring and damper system, it’s a tradition
system in which trade off between vehicle ride and comfort of the driving.
7 | P a g e

Figure 1-Suspension system
Figure 2- Active and passive suspension function
Question and Answer
As the figure indicated above passive suspension system. A good design of suspension system
can provide some comfort but also leads to unstable ride of vehicle. There are lots of design have
been given for passive system but none of them is providing compromise elimination of
stabilities of vehicle.
Active suspension system:
8 | P a g e

Question and Answer
The basic difference between active and passive suspension system is that in active suspension
system, spring and damper both are replaced with force of actuator. The benefit of this system is
that it can gain or lose energy from the system with slow motion, this slow motion provide less
turbulence to the driver. The application of force is independent of displacement across the
suspension system. In other word we can say that active suspension system provide automatic
control of vertical movement in such a way that it provide comfort to the operator as well as
stability to the vehicl (Kurtz, 2016)e.
Solution 2b.
As discussed earlier, hydraulic damper in automobile used to dissipates energy obtained by
vehicle due to vertical movement of vehicle. The design criteria for hydraulic damper will e as
follows.
Damper is used to absorb the shock in the vehicle, based on these requirements, therefore during
the process of selecting the material for damper for automotive application we have to consider
the following mechanical properties.
 Ultimate tensile strength.
 Yield strength
 Ductility, wear resistance, toughness and hardness
 Corrosion resistance
 Erosion resistance.
During operation damper also utilizes some mechanical limits these are
 Modulus of elasticity
 Elastic limit
 Elongation
 Proportional limit
 Yield point strength
 Tensile strength
 Fatigue limit
 Stiffness
The ultimate tensile strength and yield strength are most important property for material for
hydraulic damper. The material can be utilised for these purpose is
 High speed steel or alloy steel with high working stress
 Patented cast steel is suitable for hydraulic damper
 Hardened and tempered carbon steel
 Chromium and vanadium alloy steel etc (Babitsky, 2012).
9 | P a g e

Question and Answer
Solution 2c.
The most important design criteria in hydraulic damper are strength of top and bottom
connecting rod and thickness of cylinder. The material used in for rod is same as material used in
for piston of hydraulic cylinder, and this material is C40 or EN8-B ground and hard chrome
plated rod. Recent journals and article, suggest that there is use of stainless steel of 304 grades.
Selection of cylindrical tube depends upon its design and size of cylinder and working medium
of the cylinder. Since the working medium is fluid in case of damper with high pressure, in this
condition either increase the thickness of the wall of cylinder or choose a material that has
capacity of cope with the required stress. The most widely used in this category is ASTM 106
low carbon steel is used.
The hydraulic absorber has function to carry loads at high pressure including to transmit load and
store energy, each function has associated material index, material with high value of the
appropriate index maximise the aspect of parameter of individual component and in is generally
independent of details of the design (Kalpakjian & Schmid, 2011).
Solution 2d
There is several method of selecting the material like weighted property method, digital logic
method, Performance index method, analytical hierarchical method etc. one of them is limits on
property method. In this method is generally used when there is large alternative of material is
available. The performance of the material is described by range of three mechanical attributes of
properties, they are lower limit, Upper limit and required limit for mechanical properties. This is
very simple method. In this process just we have to match the required property of material with
available range of property for particular material. If material property out of range according to
specified material then we simply reject it and repeat6 the same process for next alternate
material. If specified limit is within the range of material then select. E.g. Suppose there is
pipeline in which we required 600 MPa, and there is available range of pipe yield strength is 550
to 700 Mpa, in this condition the required specification of yield strength comes in the range of
available pipe, then we can select the material. This process works like this only. Minimum
requirement is the range should be available for required materials (Kutz, 2006).
10 | P a g e

Question and Answer
References
Babitsky, A. (2012).
Dynamics and Control of Machines. Laughborou: Springer.
Creations, A. (2017, 11 30).
Data sheets for over 120,000 metals, plastics, ceramics, and
composites. Retrieved from Material Property data:
http://www.matweb.com/search/PropertySearch.aspx
Farag, M. M. (2014).
Materials and Process selction for engineering design (3rd ed.). Boca
Raton: CRC Press.
Kalpakjian, S., & Schmid, S. R. (2011).
Manufacturing and Engineering technology (6th ed.).
Singapore: Prentice Hall.
Kurtz, S. (2016).
UHMWPE Biomaterials Handbook: Ultra High Molecular Weight (3rd ed.).
London: Elsevier.
Kutz, M. (2006).
Mechanical Engineers’ Handbook: Materials and Mechanical Design. (3rd,
Ed.) New York: John Wiley & Sons.
Material Selection using CES edupack. (2010).
Granta Design, 1-57.
11 | P a g e