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Design Optimization of an Automobile Connecting Rod Using FEM

A Comparative Study of Optimal Shape with a Two- and Three-Dimensional Models

Hassan S. Hedia, Ismail M. R. Najjar and Saad M. Aldousari
From the journal Materials Testing

Abstract

In automotive engines, the connecting rod is subjected to high cyclic loads. These are represented by high compressive loads due to combustion, and high tensile loads due to the connecting rod mass of inertia. The main objective of this study is to optimize the shape of a connecting rod in an automobile engine. A model of the connecting rod has numerically been built and has been solved by the Finite Element Method (FEM) using the ANSYS package to determine the stresses distribution over the entire rod. In addition, the transition force analysis of the connecting rod and the verification of the analysis are shown. The aim of the optimization has been to minimize the respective Von Mises stresses which occur at connected rod in both cases, i. e. compressive loads coming from the gas pressure at maximum engine output and the bending loads resulting from the inertia force at the maximum engine power. The weight of the connecting rod should be maintained to prevent increasing of the inertia force. The results of this study indicate that the maximum compression stress occur at compressing loads at the small end section of the connecting rod. Optimizing the radius at the small end decreases such stresses. On the other hand, the inertia forces of the connecting rod mass cause a maximum bending stress at the large end section. By changing the shape and geometry of this section the maximum Von Mises stresses are reduced by 16.5 %, as compared to the original design. A buckling analysis has been carried out for the original and the optimized model and the results have been compared. The load factor (critical load / applied load) is increased by 7 % compared to the original design. Finally, a shape optimization for connecting rod reduces the stresses over the entire rod.

Kurzfassung

Designoptimierung eines Pleuels mittels FEM – Eine Vergleichsstudie der optimalen Form mit zwei- und dreidimensionalen Modellen. In Motoren werden Pleuel hohen zyklischen Beanspruchungen unterworfen, die sich vor allem durch hohe Druckbeanspruchungen infolge der Verbrennung und in hohen Zugbeanspruchungen infolge der Massenkraft der Pleuel äußern. Das Hauptziel der diesem Beitrag zugrunde liegenden Studie war es, die Form des Pleuels zu optimieren. Hierzu wurde ein numerisches Modell des Pleuels entwickelt und mittels der Finite Elemente Methode (FEM) unter Verwendung des Programmpaketes ANSYS wurde die Spannungsverteilung über das gesamte Pleuel bestimmt. Darüber hinaus werden die Übertragungskräfte des Pleuels sowie die Verifikation der Analysen dargestellt. Das Ziel der Optimierung bestand in einer Minimierung der entsprechenden Von-Mises-Spannungen im Pleuel für beide Fälle, also für Druckbeanspruchungen infolge des Gasdruckes und für Biegebeanspruchungen bei maximaler Motorleistung. Das gewicht des Pleuels sollte beibehalten werden, um eine Zunahme der Massenkräfte zu vermeiden. Die Ergebnisse dieser Studie zeigen, dass die maximalen Druckspannungen bei maximaler Druckbeanspruchung an den kleinen Enden des Pleuels auftreten. Eine Optimierung des Radius an dem kleinen Ende führt zu einer Absenkung dieser Spannungen. Auf der anderen Seite verursachen die Massenkräfte des Pleuels am großen Ende maximale Biegespannungen. Unter Veränderung der Geometrie dieses Bereiches können die maximalen Von-Mises-Spannungen um 16,5 % gegenüber dem ursprünglichen Design reduziert werden. Es wurde eine Berechnung auf Knickung an dem ursprünglichen und dem optimierten Modell durchgeführt und in Hinblick auf ein optimales Design wurden die Ergebnisse verglichen. Der Lastfaktor (kritische/einwirkende Beanspruchung) ist gegenüber dem ursprünglichen Design um 7% höher. Schließlich ist festzustellen, dass mit einer Formoptimierung die Spannungen im gesamten Pleuel reduziert werden können.


Prof. Dr. Hassan S. Hedia, born 1959, is professor of Materials and Solid Mechanics. He is working at the King Abdulaziz University, KSA. He received his BSc in 1981 from the Mechanical Engineering Department of the Cairo University, Egypt, and his MSc in 1989 in Production Engineering, from the Mansoura University, Egypt. 1996 he obtained his PhD from the Mechanical Engineering Department at the Leeds University, UK, and the Mansoura University, Egypt under channel system. His field of interests are advanced materials, fracture mechanics, stress analysis, and biomechanics.

Dr. I.M.R. Najjar, born 1966, is an assistant professor at the King Abdulaziz University, KSA. He receiced his BSc and MSc in 1989 and 1993 from the Mechanical Engineering Department., Collage of Engineering, King Abdulaziz University, KSA. His PhD he obtained in 2003 from the Warwick University, United Kingdom. His field of interest is mechanical measurements.

Dr. S. M. Aldousari, born 1956, is an assistant professor at the King Abdulaziz University, KSA. 1980 he received his BSc from the Mechanical Engineering Department, Colleage of Engineering, King Abdulaziz University, KSA, and his PhD and MSc in 1993 from the Bradford University, United Kingdom. His field of interest is manufacturing technology.

Eng. Ghazi H Alsoruji received his BSc in Mechanical Engineering from the King Abdulaziz University (KAU). Four years field experiences in one of the biggest desalination and power plant in Saudi Arabia “Shoiba Desalination and Power plants”. Areas of interest are: modeling, design, optimization, simulation, and manufacturing in mechanical engineering.


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Published Online: 2013-05-26
Published in Print: 2010-11-01

© 2010, Carl Hanser Verlag, München