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Article
ASSESSMENT OF FATIGUE CRACK RATE UNDER CYCLIC LOADING

Author: Muhanad Hamed Mosa
Journal: Al-Qadisiyah Journal for Engineering Sciences مجلة القادسية للعلوم الهندسية ISSN: 19984456 Year: 2014 Volume: 7 Issue: 3 Pages: 254-264
Publisher: Al-Qadisiyah University جامعة القادسية

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Abstract

Fatigue crack growth (FCG) in structures subjected to variable amplitude (VA) loading is a complex phenomenon. Analysing of FCG rate is important for the reliable life of engineering structures. It is difficult to model all the parameters influence FCG correctly due to the random nature of the VA loading as well as the number and complexity of the mechanisms involved in the FCG problems. . It has been found from the literature review that no universal model has been developed to analyse the crack growth condition under VA loading. In addition, no general understanding has also been agreed among researchers for any available models. Therefore, the main objective of this work is to investigate the FCG under VA loading based on FCG models also to propose a suitable model for VA loading. The work describes some of the FCG models for predicting the fatigue lives and FCG rates. For the simulation part of this study, towards prediction of crack propagation under cyclic, variable and random loading were used. The results had been carried out based on the Austen, modified Forman and NASGRO models. There are many factors affecting the FCG, which shown with great influence such as; initial crack length, load sequence, aspect ratio and stress ratio.


Article
CRACK TIP BEHAVIUOR UNDER DIFFERENT LOAD RATIO WITH CONSTANT Kmax

Author: Muhanad Hamed Mosa
Journal: Al-Qadisiyah Journal for Engineering Sciences مجلة القادسية للعلوم الهندسية ISSN: 19984456 Year: 2015 Volume: 8 Issue: 1 Pages: 14-20
Publisher: Al-Qadisiyah University جامعة القادسية

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Abstract

In this paper, fatigue crack growth rate (FCGR) analyses were conducted on compact specimens of an AISI 4340 alloy to study the behavior over a range in load ratios (0.1 ≤ R ≤ 0.95) and constant maximum stress intensity factor (Kmax) condition. Previous study had indicated that high R > 0.7 and constant Kmax test conditions near threshold conditions were suspected to be free crack-closure and that any differences were caused by Kmax effects, from threshold to near fracture conditions. Cracks in high-cycle fatigue (HCF) components spend a large portion of their fatigue life near threshold conditions. In order to characterize the evolution of damage and crack propagation during these conditions, fatigue crack growth rate (FCGR) data at threshold and near-threshold conditions are essential in predicting service life and in determining the proper inspection intervals. Fatigue crack growth model, namely Forman were examined, this model implicit the effect of R ratio and ease of curve fitting to measured data. The Forman model may be suggested for use in critical applications in studying fatigue crack growth for different load ratios.


Article
FINITE ELEMENT MESH SIZE IN FATIGUE LIFE EFFECT

Author: Muhanad Hamed Mosa
Journal: University of Thi-Qar Journal for Engineering Sciences مجلة جامعة ذي قار للعلوم الهندسية ISSN: 26645564/26645572 Year: 2016 Volume: 7 Issue: 1 Pages: 18-27
Publisher: Thi-Qar University جامعة ذي قار

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Abstract

Pipe elbows are consequential parts in a piping system. When a thin-wall elbow is exposed to variable amplitude loading as internal cyclic pressure, piping elbows are vulnerable to crack at the crown. This paper presents a technique to predict the fatigue life of elbows with the application of variable amplitude loadings (VAL). For this goal, the finite element analysis technique was being used for the modeling and simulation. The fatigue life prognostication was carried out using the finite element based fatigue analysis codes. Numerical life prognostication results of three types of elbows (135o ,45o and curved ) under VAL are presented and discussed. Varying elbows shows different fatigue life behavior, the curved one gives better life. The two types of elements (Tet4 and Tet10) were investigated with optimum mesh size to get the maximum principle stress. The simulation results showed that more studies on the piping elbows necessity to be performed in order to obtain more delicate fatigue life.

تعتبر الانابيب الكوعية من العناصر الهامة في الانظمة الخاصة بشبكات الانابيب , فعندما يتعرض الكوع الرقيق الجدران لاحمال متغيرة السعة كالاختلافات الدورية في الضغط الداخلي لتلك الانابيب يكون عرضة الى نشوء صدع في الانبوب . يقدم هذا البحث تقنية للتنبؤ بعمر الانبوب الكوعي حيث شمل البحث مدى واسع من الاحمال المتغيرة حيث تم استخدام تقنية تحليل العناصر المحدودة للنمذجة والمحاكاة. وقد تم تنفيذ هذه الطريقة باستخدام ثلاث انواع من الزوايا لتلك الانابيب ( 45 درجة ، 135 درجة والانابيب المنحنية) و تم اجراء الدراسة والمناقشة للنتائج لهذه الانواع الثلاثة, ولقد تبين بان اختلاف الزوايا والشكل في الانابيب الكوعية يؤدي الى الاختلاف في اعمار هذه الانابيب اعتمادا على انواعها ولقد تبين من خلال هذه الدراسة بان افضلها عمرا هي الانابيب المنحنية .عند اجراء النمذجة تم فحص هذين النوعين من عناصر (Tet4 وTet10) مع الحجم الامثل للشبكة الخاصة بالعناصر المحددة وذلك للحصول على أقصى قدر من الاجهاد الاساسي او الاجهاد الاقصى ولقد وأظهرت نتائج المحاكاة ضرورة اجراء المزيد من الدراسات على الأنابيب الكوعية وذلك من أجل الحصول على نتائج اكثر دقة للتنبؤ بحياة تلك الانابيب.

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