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Failure Analysis of Master Rod in Radial Engine (Coursework Sample)


Radial Engine is a reciprocating type IC Engine Configuration in which, using the master rod and the articulating rod assembly, the pistons are connected to the crankshaft. The master rod’s function is to translate the alternating translating motion of piston into the crankshafts rotational motion. The failure of the Master Rod was one of the most frequent reasons for the failure of the Radial engine. The aim of this project was to do the Failure Analysis of the Master Rod of Moki-S 400cc 5 cylinder Radial Engine with the help of ANSYS Workbench.
The Radial Engine was first drafted in SOLIDWORKS and then translated into ANSYS Workbench. Transient Structural Analysis, Static Structural Analysis, Eigen value Buckling and Fatigue tool analysis were performed on the radial engine and the master rod. The Master rod was then optimised by changing the material from Structural steel A36 to Aluminium alloy 7075-T6 and the positions of the lubrication holes were also shifted. The failure analysis was performed on this Optimized master rod and the results were compared with the analysis results of the Existing Master rod.


The Radial Engine is an IC style reciprocating engine in which, like the spokes of a wheel, the cylinders radiate outward from a central crankcase. It depicts a stylized star when viewed from the front and is ofter called the star engine. The pistons are connected to the master rod and articulating rods in the radial engine. One piston is connected to the master rod to which the crankshaft can be directly mounted. The remaining pistons are fixed to the rings around the end of the master rod with the help of the articulating rods.
Figure 1: Moki-s 5 cylinder Radial Engine
The radial engines firing order is the series in which the power event happens in various cylinders. The firing order is made in such a way to provide balance to the engine and also eliminate vibrations to the maximum extent possible. The firing order in radial engines follows a particular pattern because during its rotation, the firing impulses must obey the motion of the crank throw. In inline engines, the firing order can vary but the order is organized in such a way that the firing of cylinders is distributed equally along the crankshaft. Six-cylinder inline engines have a firing order of 1-5-3-6-2-4 in general. In opposing engines, the cylinder firing order may typically be specified in pairs of cylinders, as each pair fires across the main centre bearing. The firing order is 1-3-5-2-4 for five cylinder radial engines and the firing order of a four-cylinder radial engine is 1-4-2-3, but on another model it can be 1-3-2-4.
To mitigate the inertial forces from its motion, the master rod must be light enough, stiff enough to allow proper coupling with the crank-pin and the piston-pin and solid enough to bear the external loading. In particular, a certain part of the master rod may be treated as an alternating mass, thus directly influencing the maximum calue of the alternating forces.
The failure of the master rod usually referred to as the collapse of the master rod or ‘rod-throw’ was one of the most frequent reasons for the catastrophic failure of the engine in airplanes using radial engines which throws the damaged rod across a piston side.
The master rod is subjected to tension,compression, fatigue loading and buckling during engine operation. In most instances, the occurrence of the master rod failure was the main reason behind causing catastrophic engine failure, and sometimes such a failure can be attributed such a failure can be attributed to the shank of the broken master rod, particularly when there is a possibility especially when there is a possibility of being forced through the side of the crank-case rendering the engine irreparable.
The Finite Element Analysis which was carried out on Master rod in research papers mainly focuses on the critical section where transition takes place between the piston end and the crank end. In this project our aim was to determine how fretting fatigue, Euler type collapse and the position of lubrication holes have an effect on the failure of the Master rod.
Chapter 2
This chapter of the report addresses the research work carried out by researchers in the field of failure analysis of connecting rods. This formed the basis of motivation for further research work.
Sunil Kumar HE et al.,[1] This paper presented the stresses developed in the master rod in static and dynamic loading conditions. Based on the results obtained, the master rod was remodelled to improve its fatigue life by using FEM approach. Harmonic analysis was also conducted to find the various plots of amplitude and frequency against rotational velocity for structural steel and aluminium alloy. Results obtained after carrying out the static and dynamic analysis gave the stresses produced at the transition region between the crank end and the piston end in the master rod under tension.
C Juarez et al.,[2] This paper described the findings of an investigation of a malfunction study of a connecting rod of a diesel engine that was used in electrical energy generation. Visual inspection, magnetic particle inspection, fractography, tensile and hardness checking, chemical testing, microanalysis and metallography were the experimental methods and testing techniques used in the failure analysis investigation. The connecting rod was made from a low alloy steel SAE 4140. For the application, the mechanical properties, chemical composition and microstructure were suitable. The fracture occurred at the shank region of the connecting rod closer to the big end. The connecting rod’s lubrication channel was found to be the origin of the fracture. A tungsten based material was found in the lubrication channel, embedded on its surface, presumably deposited from a machining tool during defective process in manufacturing. This aregion served as a nucleation site for the spread of cracks through the connecting rod, reducing its segment causing catastrophic fatigue mechanism failure.
K. Baria et al.,[3] In this paper investigation was done for a failed connecting rod for the potential pathways contributing to its untimely failure and the root causes of the failure. FEA Analysis was used to validate the results. In order to ascertain the root cause of the failure, visual analysis was mainly used.
In order to prevent similar types of failures in the future, the presumption of this study was to directly make changes to its current processes and design.. A Scanning Electron microscope was used to examine the fracture mode mechanisms and optical microscopy to study microstructures. It was concluded that the root cause of the premature failure that led to micro cracking during fatigue loading of the connecting rod was the existence of scale build up inclusions.
Priyank D. Toliya et al.,[4] The purpose of this study was to examine how the failure in the connecting rod of an automotive engine occured. The author has chosen the Diesel FM-70 engine’s connecting rod made up of the material Aluminium 6351. The elastic strain, von Misses stress, total deformation in the current connecting rod design was calculated using FEM Software Ansys 12.1 by static analysis for the defined loading conditions. For the study, static loads acting on the connecting road were used and subsequent work was carried out to introduce a safe design and enhance its fatigue life. In the end, experimental outcomes and the values of software analysis were compared.
Manish Kumar et al.,[5] In this paper the strain life theories were studied, FEA results for stresses was presented and the design methodology was covered. The connecting rod was not only subjected to pressure from the con-rod mechanism but it was also subjected to inertia forces, as the connecting rod works in variably complicated mechanisms. Due to the reversible cyclic loadings, the connecting rod was subjected to tremendous fatigue cycles. This fatigue phenomenon developed due to repetitive stresses in the connecting rod causes hazardous splits and damage. Buckling, fatigue, yield characteristics are also used to evaluate the performance of engine connecting rods to optimize vibration by reducing design mass. Different cross-sections of the rod like like I section, Rectangular section, H section, + section and circular sections have an important role in architecture and their applications have also been researched in this paper.
Antonio Strozzi et al.,[6] This paper presented several uncommon and typical modes of failure for con-rods of IC engines and comments are made from the poiint of view of stresses. Advanced mathematical models, conventional equations and with Finite Element Analysis (FEA) forecasts helped to explain their fractures.
By addressing the components that make up the connecting rod itself, the small end, the big end and the shank, the series of failures occuring in the connecting rod was addressed seperately.
Shailesh Govindbhai Goyani et al.,[7] The aim of this paper was to cite the comparison between two materials of the connecting rod for parameters like Von-misses stresses, strain, tension and compression loads, total deformation, bending moments and so on with the help of ANSYS.
From the above literature surveys, we got the information about the different types of failures occurring in the connecting rods. We also understood the critical sections in the connecting rod which are important for improving the life of the Master rod to prevent rod-throw in radial engines. It also gave us information about the various Tribological factors which may lead to the failure of the connecting rods.
Chapter 3
The following research gap were found during our literature survey
* Many existing literature surveys focus on the failure in the transition area of the master rod between the piston end and the crank end.
* Our project aims in determining how Euler type collapse, fretting fatigue and position of lubrication holes cause failure in the master rod.
The objectives of our project are as follows:
* To determine how fretting fatigue, Euler type collapse and position of lubrication holes contribute to failure.
* To determine the primary cause of failure in the shank region.
* To optimize the master rod in accordance with the results obtained from failure analysis and perform failure analysis on the optimized master rod and then compare results with existing master rod.
Chapter 4
This chapter is devoted to the explanation of methodology incorporated in doing the failure analysis of the radial engines master rod...

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