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Analysis of Crack Propagation in a Thick-Walled Cylinder under Fatigue Loading

Thesis Info

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Author

Salam, Iftikhar Us

Program

PhD

Institute

National University of Sciences & Technology

City

Islamabad

Province

Islamabad

Country

Pakistan

Thesis Completing Year

2008

Thesis Completion Status

Completed

Subject

Mechanical Engineering

Language

English

Link

http://prr.hec.gov.pk/jspui/handle/123456789/521

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676727701256

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Reliability of materials and structures in the form of thick-walled cylinders is of critical importance to many industries including power, nuclear, chemical, armament, and food processing industries. Catastrophic failure of these cylinders can put the human life and the surroundings at very high risk. For this reason, the integrity of the cylinder should be guaranteed. The integrity of nearly all engineering structures is threatened by the presence of cracks. Structural failure occurs if a crack larger than a critical size exists. Although most well designed structures initially contain no critical cracks, subcritical cracks can grow to failure under fatigue loading, called fatigue crack propagation. Fatigue failure that is failure under repeated or cyclic loading is a serious concern of engineering design. Under fatigue loading the component may fail at a stress level that is far below its yield strength. In present research the fatigue crack propagation, in a thick- walled cylinder, is analyzed through detailed experimental work and finite element analysis and the fatigue crack growth life of the cylinder, with crack at the bore surface, has been predicted. Extrusion process induces microstructural anisotropy in the thick-walled cylinder. The intensive experimental work, with the help of laboratory tests on the material under investigation, explores the details of the material and the microstructure-properties relationship in the longitudinal and transverse orientations. The yield and tensile strength in two orientations are not significantly different. However, percent elongation, reduction in area, impact strength and fracture toughness of the material are superior in the axial direction. A marked impact of anisotropy is found on the fatigue properties and shorter fatigue life in the transverse direction was obtained, which is 41 to 62 % lower in the tested stress range of 129 to 47 MPa. The theoretical part of the study includes modeling and simulation based on finite element method and the numerical technique is employed for the simulation of fatigue crack propagation. The finite element analysis, based on linear elastic fracture mechanics (LEFM) combined with the Paris law, suitably predicts the fatigue life and provides the results that are in good agreement with the experimental results. Both the experimental and numerical results of the crack growth data at different stress levels were found in good agreement all along the Paris regime. In the near threshold region the predicted values are conservative. With implementation of the present scheme of work the fatigue crack growth life of the thick-walled cylinder, with internal axial crack, has been predicted.
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مولانا محمد عثمان فارقلیط

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Genome Wide In-Silico Analysis of the Ppos and Pox-A Gene Families in the Selected Plant Species

Genome wide analysis of the genes responsible for polyphenol oxidase (PPO) or peroxidase (POX) enzymes was performed in nine plant species namely (Carica papaya), model plant dicot (Selaginella moellendorffi), monocot (Zea mays), legumes (pisum sativum, Vigna angularis), cereals (Avena sativa, Setaria italic and Oryza sativa) and fruit (Morus notabilis) species. We identified 135 PPO and 1645 POX genes in the selected plant species during the genome wide distribution analysis. . The result showed that A.sativa and P. sativum had no PPO genes and a few number of POX genes were found in these plants. The synteny analysis of PPO genes in seven plant species excluding A.sativa and P.sativum revealed higher degree of conservation, recommending that these genes occurred before monocot/ eudicot divergence. The gene ontology (GO) analysis showed that PPO gene (Accession no DQ532396.1; 577 amino acids) is localized maximum in chroplast (43.1%) with score of 2.156, molecular function (47.4%), biological process (53.7%) and cellular component (13.9%). While the POX protein (Accession no DQ855429.1; 335 amino acids) is highly founded in the extracellular part of the cell membrane (62.2%) with score 3.108, molecular function 49.8%, biological process 50.9% and cellular component 61.3%. Among the identified PPO and POX genes were reported to be (91.15%) and (85.21) moderately or highly expressed. The network analysis showed that PPO and POX genes had 21, 21 nodes, 100, 97 edges, 9.52, 9.24 average nodes and 0.876, 0.539 average local cluster coefficient respectively. The POX genes were located in sub-telomeric section of chromosomes in the form of clusters. This study about genome-wide investigation and consideration of gene-expression patterns generated the valuable evidence on PPO and POX gene families that will be helpful for improving crop production in monocot or dicot plants