Effect of crack configuration and pre-crack length on stress intensity factors: Study of the tearing mode using a three-dimensional finite element model

Hassan S. M. Hedia; Mohamed A. N. Shabara; Ahmed A. Fattah; Mahmoud M. K. Helal

doi:10.3139/120.100691

Article

Effect of crack configuration and pre-crack length on stress intensity factors

Study of the tearing mode using a three-dimensional finite element model

Hassan S. M. Hedia , Mohamed A. N. Shabara , Ahmed A. Fattah and Mahmoud M. K. Helal

Published/Copyright: May 26, 2013

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From the journal Materials Testing Volume 47 Issue 10

Abstract

In this paper, the results for the stress intensity factor of a mode III (tearing mode) have been investigated using the method of finite element analysis. A compact tension specimen containing a pre-crack and subjected to out-of-plane tearing loads has been used. A three-dimensional finite element analysis (FEA) model using the ANSYS program has been built for specimens made of different bio-medical materials such as stainless steel, titanium, alumina, high density polyethylene(HDPE) and polymethyl methacrylate(PMMA). Such materials are used for hip and knee replacement and for dental implants. The effects of notch angle, notch tip radius and pre-crack length on the stress intensity factor for the mode III have been studied. The model was extended to study the effect of crack and bonding line separation distance on stress intensity factors for specimens made of different homogeneous materials such as stainless steel bonding with epoxy as a filler material. The number of elements along the crack front and crack tip has been varied to determine its effects on the stress intensity factors. It is concluded that the pre-crack must be greater than or equal to 33% of the total crack lengt and the notch must be a blunt notch in order to obtain the stress intensity factor, K_II_I, independently, of the crack notch angle. However, the stress intensity factor is independent of the crack and bonding line separation distance when it is less than or equal to 15% of the specimen width. The results for the stress intensity factors, K_II_I, are obtained using a linear elastic fracture mechanics (LEFM) approach.

Kurzfassung

Im vorliegenden Beitrag wird die Ermittlung von Spannungsintensitätsfaktoren für den Bruchmodus III an CT-Proben vorgestellt. Unter Nutzung des Programmes ANSYS wurde ein dreidimensionales FE-Modell aufgestellt für Proben aus verschiedenen Biowerkstoffen, wie hochlegierte Stähle, Titan- und Aluminiumlegierungen sowie HDPE und PMMA. Diese Werkstoffe werden unter anderem für Hüft- und Knieprotesen und für Dentalimplantate verwendet. In der Studie wurden die Auswirkungen des Kerbradius’ und der Anrisslänge auf den Spannungsintensitätsfaktor untersucht. Das ursprüngliche Modell wurde erweitert, um die Auswirkungen des Abstandes zwischen dem Riss und einer Fügelinie zu untersuchen, wie sie bei verschiedenen homogenen Werkstoffen, beispielsweise bei einer Klebverbindung zwischen einem austenitischem Stahl und einem Epoxydharzkleber vorliegt. Es wurde wiederum die Zahl der Elemente an der Rissspitze variiert, um die Effekte der Elementierung auf den Wert des Spannungsintensitätsfaktor zu untersuchen. Es stellte sich heraus, dass zur sicheren Bestimmung des Spannungsintensitätsfaktors unanbhängig vom Risswinkel die Anrisslänge größer 33% der Gesamtrisslänge sein muss und dass es sich um einen runden Kerb handeln muss. Der Spannungsintensitätsfaktor erwies sich als unabhängig vom Abstand zwischen dem Riss und der Fügelinie, wenn dieser weniger als 15% der Probenbreite beträgt. Die Ergebnisse für die Spannungsintensitätsfaktoren K_III wurden mittels der linear elastischen Bruchmechanik ermittelt.

Associate Professor Dr. Eng. Hassan S. M. Hedia, born in 1959, studied Mechanical Engineering at Cairo University from 1976 to 1981. In 1996, he finished his MSc. and PhD. at the Production Engineering Department at Mansoura University. He works as an Associate Professor in the Production Engineering and Mechanical Design Department within the Faculty of Engineering at Mansoura University. His research activities cover the fields of stress analyses, fracture mechanics and materials testing.

Prof. Dr. Mohamed A. N. Shabara, born in 1945, studied mechanical engineering at the El-Mansoura Higher Industrial Institute and at Pennsylvania State University from 1967 until 1971. Today he is professor for mechanical design at Mansoura University. His current research activities include machine design, stress analyses, fracture mechanics and materials testing.

Prof. Dr. Ahmed Abdul Fattah, born in 1945, studied Mechanical Engineering as well as Machine Design and Production Engineering in Cairo. In 1982, he completed his Ph. D. in Fracture Mechanics at the Indian Institute of Technology in Bombay, India. He is a professor at the Production Engineering and Mechanical Design Department within the Faculty of Engineering at Mansoura University in Egypt.

Eng. Mahmoud M. K. Helal, born in 1978, studied Mechanical Engineering in the Production Engineering and Mechanical Design Department at Mansoura University. In 2005, he finished his MSc. He works as an assistant lecturer in the Production Engineering and Mechanical Design Department at Mansoura University.

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Published Online: 2013-05-26

Published in Print: 2005-10-01

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https://doi.org/10.3139/120.100691