Optimum Design of Connecting Rod – A Review

Abstract

This study discusses a comprehensive review of the optimal design of the connecting rod used in internal combustion engines and compressors. The connecting rod is an important part and a major component that is produced in large quantities for automobile engines. Its purpose is to link the piston to the rotating crankshaft to create a mechanism for the movement reciprocating of the piston. Carbon steel is commonly used in the manufacture of connecting rods, but there is a growing trend towards utilizing aluminum alloys. Objective of this study is to optimize the shape of the connecting rod in an automobile engine. The optimization aims to minimize the stresses experienced by the connecting rod under both compressive loads from maximum engine output and bending loads caused by the inertia force during maximum engine power with a focused on reducing its weight. Various stresses and deformations need to be considered when designing the connecting rod, along with the comparison of different materials. Additionally, it is important to explore various software and Finite Element Method (FEM) packages that can be utilized for the modeling and analysis of the connecting rod.

Full text

Journal of Mechanical Design and Vibration, 2024, Vol. 11, No. 1, 1-9
Available online at http://pubs.sciepub.com/jmdv/11/1/1
Published by Science and Education Publishing
DOI:10.12691/jmdv-11-1-1
Optimum Design of Connecting Rod – A Review
Maher Rehaif Khudhair*, Farah Kamil, Mohannad A. Kadhom, Faeq H. Gburi
AL-Dewaniyah Technical Institute AL-Furat Al-Awsat Technical University, Iraq
*Corresponding author:
Received February 20, 2024; Revised March 22, 2024; Accepted March 29, 2024
Abstract This study discusses a comprehensive review of the optimal design of the connecting rod used in
internal combustion engines and compressors. The connecting rod is an important part and a major component that
is produced in large quantities for automobile engines. Its purpose is to link the piston to the rotating crankshaft to
create a mechanism for the movement reciprocating of the piston. Carbon steel is commonly used in the manufacture
of connecting rods, but there is a growing trend towards utilizing aluminum alloys. Objective of this study is to
optimize the shape of the connecting rod in an automobile engine. The optimization aims to minimize the stresses
experienced by the connecting rod under both compressive loads from maximum engine output and bending loads
caused by the inertia force during maximum engine power with a focused on reducing its weight. Various stresses
and deformations need to be considered when designing the connecting rod, along with the comparison of different
materials. Additionally, it is important to explore various software and Finite Element Method (FEM) packages that
can be utilized for the modeling and analysis of the connecting rod.
Keywords: connecting rod, optimization, design, material selection, FEM
Cite This Article: Maher Rehaif Khudhair, Farah Kamil, Mohannad A. Kadhom, and Faeq H. Gburi,
“Optimum Design of Connecting Rod – A Review.” Journal of Mechanical Design and Vibration, vol. 11, no. 1
(2024): 1-9. doi: 10.12691/jmdv-11-1-1.
1. Introduction
Connecting rod is a major link of the internal
combustion engines and one of the most important
components employed in automobiles, trucks, and buses.
And principle working its connects the piston and the
crankshaft and contributes to convert the reciprocating
motion of the piston into rotatory motion of the crankshaft.
Usually, it's applied to reciprocating internal combustion
(I.C.) engines, like the ones found in automobiles. Spark
ignition engines take a mixture of fuel & air, compress it,
and ignition it was using a spark plug. The terms
reciprocating' is given because of the motion that the
crank mechanism through it. The connecting rod is
subjected to highly-cycle of dynamic or fatigue loading.
Therefore, consideration must be given to the effect of
each gas forces and inertia forces. Many of research work
have been carried out for optimization approach as a
material selection or stress analysis [1,2,3,4,5]. Figure 1
shows the parts of connecting rod. The connecting rod is
typically a durable and strong metal rod, usually made of
steel or aluminum alloy, with a specific shape and design.
It consists of two ends: the small end and the big end. The
small end of the connecting rod is connected to the piston
pin or wrist pin, while the big end is connected to the
crankshaft journal. During the engine's operation, the
connecting rod experiences high mechanical stresses and
undergoes both tensile and compressive forces. It must be
able to withstand these forces without deformation or
failure. For this reason, connecting rods are engineered to
be robust and lightweight to minimize inertia and
maximize engine efficiency. Connecting rods are designed
with careful consideration given to factors such as length,
weight, strength, and balance. The length of the
connecting rod and its ratio to the stroke length of the
piston affects the engine's mechanical advantage and
overall performance characteristics. The weight of the
connecting rod is also critical as it impacts the engine's
ability to reach higher RPMs and reduces the overall load
on the crankshaft. In high-performance engines,
connecting rods are often subjected to additional stress
due to increased power output. To address this,
performance connecting rods may be forged or made of
stronger materials to provide enhanced strength and
reliability. Its design and quality significantly impact
engine performance, durability, and efficiency.
2. Literature Review
Table 1 represents a comprehensive review of previous
studies of researchers, where it included design details
represented by the calculation of stresses and
deformations, as well as some focused on studying the
behavior of buckling under the static and dynamic loading,
in addition to experimental tests and comparing them with
numerical analysis (using the Finite Element Analysis) as
shown in the following table.

2 Journal of Mechanical Design and Vibration
Figure 1. Parts of Connecting Rod
Table 1. Literature Review
Ref.
No.
Pub.
year
Study objectives
Software / Experiment /
Theoretical
Conclusions
1 2010
Used topology optimization techniques to
reduce the weight and predicted low
maximum stress compare to the initial design.
SOLIDWORKS and
MSC/NASTRAN The optimized design is 11.7% lighter and has more
strength than the initial design.
2 2012 Interested in weight minimization and
structure simplified. ANSYS
The optimal result shows the weight of connecting rod
is lighter and long life, also can be used in the
traditional design to replace partly numerical analysis.
3 2013
Studied stressed to develop under static
loading with different loading conditions of
tension and compression at the crank end and
pin end of connecting rod. Also, designed by
a machine design approach.
PRO-E wildfire 4.0 and
ANSYS 11
The maximum value of equivalent stress has been
found be to 197.41 MPa when the crank end of
connecting rod is under tension loading for the
analytical outcome compared with numerical results. In
addition, stress is less than the yield strength of the
material and gives a safety factor is 3.2 for static load
conditions.
4 2013 Evaluated of stresses (big and small ends).
Experimental and
Numerical by Pro/E
Wildfire 4.0 and ANSYS
WORKBENCH 11.0
Stresses in the small end of the connecting rod are
greater than the stresses at the big end.
5 2013 Developed a new insight for composite
material. CATIA V5 & MSC.
PATRAN
Used two composite materials (Conventional Steel and
E-Glass/Epoxy) and same boundary conditions, and
compared to obtain results.
6 2013
Re-optimize of design of connecting rod of
universal tractor (U650) through change some
of the design variables under same boundary
and loading conditions.
CATIA 19, PRO-E and
ANSYS workbench v12 Modelled and optimized for the reduced density, and
improved life and manufacturability.
7 2013
Used of forged steel and compared with
carbon steel material during examined of
(Von misses Stress, strain, and Deformation)
and reduced of density. Also, fatigue life
analyzed.
CATIA V5 R19 &
ANSYS 13.0
Forged steel offers a higher margin of safety, enabling
weight reduction, enhanced stiffness and reduce the
stress and stiffer.
8 2013 Focused to replace of materials. ANSYS
The recently new material exhibits reduced weight and
improved stiffness characteristics. This discovery led to
a remarkable 43.48% reduction in weight and a
substantial 75% decrease in displacement.
9 2013 Investigate possibilities for reducing weight. PRO-E and ANSYS
The design and optimization of the connecting rod can
encompass both extreme loads: a tensile load aligning
with a 360 degree crank angle at maximum engine
speed, and the pressure exerted on the crank.

Journal of Mechanical Design and Vibration 3
Additionally, the current connecting rod can be
substituted with a novel one crafted from Genetic Steel.
10 2014 Examine opportunities for weight and cost
reduction in the design and manufacturing of
connecting rods and approached in two steps. ANSYS
The results of the analysis can produce extremely good
des
igns very quickly, and we can apply the best designs
there. Additionally, it was thought that the methods
used in this study would be very helpful to designers.
11 2014
Examination of the compressive stress on the
connecting rod under various loading
conditions. The numerical results will also be
used to investigate the experimental results.
Experimental and
Numerical by ANSYS It was found that there is a greater similarity between
the experimental results and the numerical results.
12 2014 Analysis of the various stresses under fatigue
loading on the connecting rod, and
optimization for both shape and weight.
SOLIDWORKS and
ANSYS workbench 11
Shape-finding technology has been employed to reduce
weight, and structural steel has a high density.
Therefore, aluminum alloy was used instead of the
original material, which results in a large weight
reduction and improved outcomes for stresses. In the
case of aluminum alloy, longevity is also increased.
Due to the large buckling stress, when analyses of
linear buckling were conducted, the maximum
deformation was 1.0072 mm. Because of the significant
multi-axially of the load, multiaxial fatigue analysis is
required to calculate the fatigue strength.
13 2014 Reviewed about optimizing the connecting
rod's design for use in car engines. CATIA and ANSYS
It is possible to make connecting rods lighter, less
expensive, and more durable. The connecting rod is
stronger and lighter than it was in the original design,
but only to a point.
14 2014
Static stress analysis has been carried out on a
connecting rod composed of two distinct
materials: E-glass/Epoxy and an Aluminum
composite reinforced with Carbon nanotubes.
ANSYS 14.0
The connecting rod fabricated with Al-2 vol. % CNTs
demonstrates a lower weight compared to the E-
Glass/Epoxy counterpart. Upon analyzing the results
for these two different materials, it was observed that
the stress induced in the Al-2 vol. % CNTs composite
is lower than that in the E-Glass/Epoxy variant.
15 2014
The main goal is to install an aluminum
connecting rod in place of the LML
Freedom's currently damaged forged steel
connecting rod.
Pro/Engineer and
ANSYS
When combined with a superior epoxy that can survive
the heat within the chamber, composite materials like
carbon fiber, which have good strength, can be used as
connecting rods. A crank shaft made of aluminum
would produce superior results and put less strain on
the connecting rod, extending its lifespan.
16 2014
Investigated and compared of the connecting
rods made of two materials (forged steel and
powder metal), and analyzing the costs of
both materials under fatigue behavior.
CATIA V5 and
ALTAIR RADIOSS
Forged steel it have best properties of (tensile and
compressive and fatigue) test. While the powder metal
its cost effectiveness.
17 2015 Stress and deformation analysis and weight
optimization Pro/Engineer and
ANSYS
Identify the areas or parts where there is a high risk of
failure. The collected data may also be utilized to
improve the performance and life cycle of the current
designs.
18 2015
describes of real time problem used Cast Iron
material and optimized with different
materials
CATIA and ANSYS
14.0 Modified design is better than the existing design.
19 2015
Analysis the stress, strain, deformation used
varying material with same solid geometry
Pro/Engineer and
ANSYS
(Al 6061) is high strength compared with (Al
6060 + B4C)
20 2015 Investigation study of the strength behavior
for the connecting rod through the engine
operation under fatigue loads.
SolidWorks and
ANSYS V14.0
The connecting rod experiences both compressive and
tensile forces, with the compressive forces significantly
outweighing the tensile forces. As a result, the design
prioritizes the accommodation of compressive forces.
21 2016 General study of properties for the connecting
rod and redesign optimization through weight
reduction and dimensions.
Numerical
(CAD Software)
Utilizing plastic material data for analysis would yield
more satisfactory results. To enhance precision in
calculating induced stresses, a finer and more detailed
meshing of the connecting rod can be employed.
Additionally, for future endeavors, we should consider
factors such as bushings, crank bearings, and damping
effects. Furthermore, incorporating bolts tightened to
their rated torque to achieve the correct preload for
analysis could yield results that closely align with the
actual component.
22 2016 Reviewed about weight optimization with
different materials. CATIA and ANSYS
14.0
Numerical results were obtained through software
utilized for modeling and analysis, facilitating the design
of connecting rods for use in automobiles. This design
process focuses on achieving weight reduction and cost
optimization while simultaneously extending the lifespan
of the connecting rod. To a certain extent, this approach
yields lighter connecting rods with enhanced strength
when compared to the original design.
23 2016 Examine the stresses generated on the
connecting rod.
SolidWorks and
ANSYS Workbench
16.2
The maximum compression stress was occur between
the pin end and the rod. While the maximum shear
stress was exist at the pin end. In addition, the
connecting rod failure can occur at either end, but there
is a higher probability of failure at the piston end as
opposed to the crank end.

4 Journal of Mechanical Design and Vibration
24 2016 Stress distribution analysis for two materials
(Aluminum and steel) on application of the
force.
CATIA and ANSYS
(mechanical APDL 14.5)
The stress intensity in an Aluminum connecting rod is
higher compared to a Steel connecting rod. Moreover,
there is significant potential for enhancing the design.
Consequently, Steel emerges as the superior choice for
connecting rods.
25 2017 The objective is to redesign, analyze, and
explore alternative materials for the
connecting rod.
CATIA V5 R21 and
ANSYS 18.1
The maximum stress examined by all materials is
approximately equal. Furthermore, the deflection of the
Aluminum 7075-T651 connecting rod is comparable to
that of the existing carbon steel (42CrMo4) connecting
rod. Notably, the Aluminum 7075-T651 connecting rod
offers a significant weight advantage, weighing
approximately 35% less than the current carbon steel
connecting rod.
26 2017 Design a connecting rod with standard
dimensions and redesign with different
materials under fatigue loading. CREO 3.0 and ANSYS
Special focus should be placed on the areas of the
design that are most susceptible to buckling under
stress in order to achieve a significantly more efficient
outcome.
27 2017
A comprehensive review focused on reducing
weight, stresses, strain, and deformations of
the connecting rod without affecting its
strength.
ANSYS
Improved the strength under the influence of the loads,
and reduced of density. In addition, the I-section design
was chosen.
28 2017
The investigation on the examination of
appropriate materials and load factors, as well
as the analysis of stress, strain, and
deformation caused by these factors.
Furthermore, a structural optimization model
for the connecting rod was developed.
SolidWorks 2016 and
ANSYS Work
Bench14.5
From the results, it can be inferred that Al6061+B4C
exhibits lower stress and deformation values in
comparison to 42CrMo4. Consequently, materials with
reduced stress levels are more desirable for the
manufacturing of connecting rods.
29 2017
Optimization of the weight of a steel
connecting rod while maintaining its original
strength. To achieve weight reduction,
titanium inserts will be incorporated without
compromising the inherent strength of the
rod.
UG NX7.0 and
ANSYS R15.0
When comparing the weight reduction of a connecting
rod made from forged steel and an Al-Ti composite, it
is evident that the latter exhibits a significant decrease
in weight. Conversely, the weight reduction for a
connecting rod composed of steel and Steel-Ti
composite is not as substantial. However, this
combination does offer an increased load carrying
capacity.
30 2017 Develop a robust model for optimizing the
structure of connecting rods used different
materials.
SolidWorks 2016 and
ANSYS Work
Bench14.5
Titanium is a considerably more expensive material
compared to aluminum metal matrix composites,
despite both materials having the same stress value.
However, titanium exhibits less deformation than
42CrMo4. Furthermore, we conducted a deformation
analysis under dynamic loading on three distinct
modes, each corresponding to different frequencies.
31 2017 Discusses the process of designing and
analyzing connecting rods subjected to fatigue
loading using various materials.
CATIA V5 R20 and
ANSYS 13.0
In regards to C70 Steel, Belgium, an optimal set of
parameters can be determined to achieve superior
performance. These parameters aim to simultaneously
reduce weight, enhance stiffness, minimize stress, and
surpass the rigidity of alternative materials.
32 2017 Reviewed of connecting rod design and
analysis using a variety of materials ANSYS
Aluminum and titanium alloys are more affordable
replacements for steel. Using composite materials,
weight may be optimized without changing the
permissible stresses and boundary conditions.
33 2017 Design and assessment of a connecting rod
used in Hero Honda Motor Cycle for fatigue
life have been conducted and evaluated.
CATIA and
FEMFAT Software
To enhance the fatigue life of the connecting rod, we
implement minor modifications to its geometry.
Specifically, for the increase the neck radius thickness
from 20 mm to 22 mm at the crank end and from 12
mm to 15 mm at the pin end. Will achieve a significant
improvement in the rod's durability, extending its
lifespan.
34 2017
Identification of problems and weak points in
the connecting rod structure, which provides
the theoretical foundation for better structural
design and optimization.
CATIA and ANSYS
Modal analysis and transient dynamic analysis were
conducted to determine the resonant frequencies of the
rod and to obtain the stress, displacement, and velocity
of the connecting rod at different time intervals. These
results are considered as a guide for researchers to lead
them to optimal design.
35 2017
Comprehensive design review. In addition to
focusing on the stresses generated during
operation as well as paying attention to ways
through which to reduce the density
ANSYS Exploring alternative weight-loss materials that could
be used in the manufacture of connecting rod
36 2018
Used Finite Element method (FEM) was
employed to analyze and gain a
comprehensive understanding of the structure
of the connecting rod.
NX 6.0 and ANSYS14.5 Slight adjustment using optimization techniques
without changing dimensions, thus achieving weight
reduction and low stress level at the same time
37 2018
To achieve an optimal design for connecting
rods that maximizes material efficiency,
minimizes costs, and enhances overall quality.
CATIA
An innovative and effective design method that
distinguished itself from the prototype by reducing
weight and effectively predicting all expectations
38 2018
Stress analysis on the connecting rod,
considering distinct compressive and tensile
loads applied individually and operating at
Cero PTC software
A large part was determined to be removed in several
areas of the connecting rod based on the results of the
numerical analysis

Journal of Mechanical Design and Vibration 5
various speeds.
39 2019 The weight optimization of the connection
rod, was conducted using the Finite Element
Method (FEM) through ANSYS Workbench.
SolidWorks and
ANSYS 16.1
Through the digital results, it was found that the Ansys
program is effective and suitable for use in engineering
designs as well as conducting analysis and optimization
processes.
40 2020 Reduce weight, adjust and replace materials
for a lightweight connecting rod without
compromising its performance
INVENTOR Software
and ANSYS
The Al7075 material exhibits a lower weight compared
to other materials under similar loading conditions, So
it is an acceptable material in its manufacture. In
addition, the Ti-6Al-4V material has a higher safety
factor under the same operating conditions. Therefore,
both Al alloy and Ti alloy are suitable choices for the
production of connecting rods.
41 2020 Reviewed to comprehend the precise behavior
of the connecting rod across various material
properties. CATIA and ANSYS
Improving the performance of the connecting rod
depends on the properties of the composite material
that can be remanufactured to achieve the required
specifications and goals
42 2020 Focus on weight reduction using optimization
techniques applied to the connecting rod used
in diesel engines SolidWorks and ANSYS
Production companies can used ANSYS software to
effectively reduce material waste, enhance profitability,
and simultaneously uphold product quality and
reliability.
43 2021 Focused on design and analysis of the
connecting rod and topology optimization. Cero PTC and ANSYS
By reducing all stresses and weight, it gives a clear
impression to reach the optimal design as a more
efficient model
44 2021 The design has been thoroughly reviewed and
improved, with enhancements made to both
the material quality and design parameters.
CATIA v5 R21,
NX NASTRAN ,
Pro-E software and
ANSYS WORKBENCH
Improving performance and achieving properties
requires modification in the composition of the
materials used
45 2021
Elastic deformations of connecting rod
components were ignored by greatly
simplifying calculations. Additionally, it
removes the requirement to compile the
equations of dynamics using partial
derivatives.
Theoretical
By comparing the calculation results with those
obtained for a two-mass model, one can identify errors
and select a design model that achieves the desired
level of accuracy.
46 2021
The main emphasis lies in exploring avenues
for reducing the mass of the two wheel
connecting rod through the introduction of
two alternative materials, in addition to the
currently used material.
CREO and ANSYS
Among the three materials tested, namely Aluminum
alloy 7475, Titanium alloy Ti-6Al-4V, and another
material (not specified), the Aluminum alloy
demonstrated superior performance. It exhibited the
lowest mass and a remarkable strength-to-weight ratio,
making it the optimal choice.
47 2021
To enhance the effectiveness of the MCI
(Measurement and Comparison Parameters),
geometric modifications are implemented to
ensure both functional requirements and
resistance limitations are met. This is
achieved through the utilization of CAD/CAE
systems, which facilitate the integration of
advanced design and analysis tools.
SolidWorks and
ANSYS 15.0
By reducing the mass of each connecting rod by
9.564%, the power of the MCI was successfully
increased without compromising their resistance,
rigidity, or the functional performance of the kinematic
torque.
48 2021
To conduct analysis under static and dynamic
loading. Also, study of weight reduction
through material optimization.
SolidWorks and ANSYS The results showed a significant improvement in
efficiency and age
49 2021
To achieve a lightweight design that fulfills
the demands for low energy consumption and
reduced vibration, the original connecting
rod's structural design is modified. The goal is
to decrease its weight, enhance natural
frequencies, minimize material usage, and
boost the energy efficiency of internal
combustion engines.
Numerical
(CAD Software)
By employing finite element analysis and prioritizing
lightweight design principles, significant improvements
have been achieved. These include a reduction in
maximum equivalent stress and an increase in low-
order natural frequency.
50 2022 To investigate potential avenues for reducing
weight and cost in the design and
manufacturing of connecting rods. ANSYS Work Bench
Upon examination, the findings indicated that both Ti-
6Al4V and 17-4Ph stainless steel met the necessary
property requirements. However, it was observed that
17-4Ph stainless steel demonstrated superior strength
and also offered a more cost-effective alternative.
51 2022
To improve the design using a topology
optimization algorithm with different factors
and multiple objectives
SolidWorks and CAE
The results showed that there is a significant decrease
in density with the quality of strength and stiffness
requirements
52 2022
To investigate the fracture of connecting rods
through the utilization of Finite Element
Analysis. By employing specialized software,
the stress and thermal factors impacting the
connecting rod could be thoroughly analyzed.
The main focus was to minimize the load
exerted on the big end and main bearing,
thereby enhancing their durability and
performance.
CATIA 5 W/F and
ANSYS 16.2
Observed that the crank end cap and piston end
experienced the lowest levels of stress among all the
loading conditions. Therefore, it is possible to reduce
the amount of material used in these specific areas,
resulting in a reduction in material costs. Moreover,
through the process of optimization, it is feasible to
replace the existing connecting rod with a new one that
is lighter in weight by approximately 15%.
Comparatively, aluminum alloy connecting rods
exhibit greater weight and displacement when
compared to magnesium and beryllium alloys.

6 Journal of Mechanical Design and Vibration
Consequently, aluminum connecting rods may
demonstrate more vibration-induced behavior or
instability.
53 2022
To obtain an accurate S-N curve for the
connecting rod material, a fatigue test was
performed. Additionally, the static strength of
the connecting rod assembly was evaluated
using an electrohydraulic servo universal
testing machine. The test results served as the
basis for validating the numerical modeling
approach.
Experimental and
Numerical by ANSYS
By optimizing the alignment between the large end
fillet of the connecting rod and the long diameter of the
rod section, not only was the mass reduced, but the
safety factor was also enhanced. Following the
structural optimization of the connecting rod, a
reduction of 5.85% in mass, a decrease of 13.7% in
maximum stress, and an increase of 16.0% in the safety
factor were achieved. This optimization approach,
along with the application of an empirical formula to
calculate the maximum stress of the connecting rod,
provides a novel analysis method for this model and
similar types in conceptual and technological design
stages. As a result, the efficiency of structural
optimization and strength analysis for the connecting
rod assembly has been significantly improved.
Table 2. Design parameters
No.
Nomenclature
Symbol
1
Maximum pressure of gas
p
2 Diameter of piston
D
3
Cross-section area of piston
A
4
Mass of reciprocating parts
mR
5
Angular speed of crank
ω
6
Angle of inclination of the connecting rod with the line of stroke
ϕ
7
Angle of inclination of the crank from top dead centre
θ
8
Radius of crank
r
9 Length of connecting rod
L
10
Ratio of length of connecting rod to radius of crank = l / r
N
3. Mathematical Model
3.1. Forces Acting on the Connecting Rod
There are several types of forces acting on the
connecting rod, which are as follows (the force acting on
the piston as a result of gas pressure and inertia of the
parts with reciprocating movement. As well as the forces
resulting from the friction of the piston rings. In addition,
the force resulting from the friction of the piston pin
bearing and the crankpin bearing). Figure 2 an explained
to forces on the connection rod and Inertia bending forces
as the equations (1 to 5). While, the Table 2 explained the
design parameters.
Figure 2. Forces on the Connecting Rod [54]
1- Force on the piston due to pressure of gas FL =
Pressure × Area
2
4
L
F p . A p D
π
= = ×
(1)
2- Inertia force of reciprocating parts FI = Mass ×
Acceleration
22
IR cos
F m . . r cos n
θ
ωθ

= +


(2)
3- Net force acting on the piston FP = Force due to gas
pressure
∓
Inertia force
PLI
F FF=
(3)
Where the –ve and +ve are signs of TDC (top dead
center) to BDC (bottom dead center) respectively, and
weight of the reciprocating parts (WR = mR . g) then:
PLI R
F F FW= ±
(4)
From figure (2) we see force of connecting rod (FC) as
in next equation:
2
2
1
PP
C
FF
Fcos sin
n
ϕθ
= =
−
(5)
4- Force due to inertia of the connecting rod for the
each point will be as follows:
2
..InertiaforceatC m CO
ω
=
(6)
2
..InertiaforceatD m dO
ω
=
(7)

Journal of Mechanical Design and Vibration 7
2
..InertiaforceatE m eO
ω
=
(8)
Inertia force per unit length at the crankpin=1 . 2,
and inertia force per unit length at the piston pin = 0
Inertia force due to small element of divisions length dx
at a distance x from the piston pin P,
2
11 x
dF m . r . . dx
l
ω
=
(9)
22
21
01
0
l
l
I
m. r
xx
F m . r . . dx
l ll
ω
ω

=∫=



(10)
When Substituting (m1 . l = m) we gets:
2
2
I
m
F .r
ω
=
(11)
5- Force due to friction of piston rings and of the piston
(F)
RR R
F D .t .n . p .
πµ
=
(12)
3.2. Bending and Compressive Stresses
From figure (3) we see the bending moment is acting on
the rod at section X – X at a distance x from P, where
bending moment due to variable force from
2
1
0x
tom . l
ω



,
and assuming the effect of the inertia force at two-thirds of
the piston from point P. In addition, the concentration of
mass is in one-third of the connecting rod from point P,
which results in the reactions are as follows:
12
33
PICI
R F ,andR F

= =


( )
2
123
XP xxx
M R. x m. r ...
l
ω

= − 

3
33
I .x
I
X
F
F . x
Ml
= −
3
2
3
I
X
Fx
Mx
l

∴= −



(13)
Now, differentiate MX with respect to x axis to get
maximum bending moment,
2
2
3
10
3
XI
dM F x
dx l

=−=



3
l
x∴=
2
2
2
1
3
33 93
I
max
Fll
M m . r .
l
ω






∴= − =




(14)
( )
max
max
M
maximum Bending Stress Z
σ
=
(15)
Where: Z – Modulus section
Compressive Stress (σc)
C max
Direct copmressive stress
σσ
= +
(16)
Figure 3. Inertia bending forces
4. Conclusion
Based on the aforementioned literature reviews, it has
been determined that significant efforts have been made to
enhance the material composition of connecting rods
through basic studies and research. The performance of a
connecting rod can be enhanced by altering the materials
utilized, as different materials possess distinct properties.
By alloying materials, the desired properties can be
achieved. In their investigations, many researchers
employed software such as CATIA, SolidWorks, NX
NASTRAN, and Creo PTC for modeling purposes, while
ANSYS software was used for analysis. Numerical
analyses were conducted to determine the magnitude of
loads (including stresses, deformation, and buckling)
experienced by a connecting rod under applied loads.
Furthermore, theoretical calculations and experimental
studies were employed to identify errors and select a
design model that achieves the desired level of accuracy.
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