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Welding is one of the most prevalent techniques for mechanical fastening of metals. Recent developments in welding technology have led to welding techniques being more readily employed in safety-critical engineering structures. Since the existence of residual stresses and material property variation around welds affects the mechanical performance and thereby structural integrity, it is essential to improve our knowledge in understanding and modelling the mechanical response of the welded structures. The present work focuses on mechanical characterizations of such structures. This work can be broadly classified into two parts; the first part investigates the residual stress distribution in welded specimens of different metals and the second part presents investigations of mechanical properties in welded specimen using full-field optical techniques.

Despite of the fact that engineering components and structures are carefully designed against fatigue failures, 50 - 90 percent of all mechanical failures are due to fatigue. Cracks can exist as a consequence of deep machining marks and voids in welds during the manufacturing processes, and metallurgical discontinuities due to the presence of foreign particles and inclusions. A comprehensive study of the expenditure relating to component fracture in the United States indicated a cost of 119 billion in 1978, or about 4 percent of the gross national product. Beside cost, the consequence of fatigue failure may result in the loss of human life, in particular in the transportation, and the oil and gas industries. Therefore, a robust fatigue life assessment is crucial to provide significant economic and safety advantages. A good fatigue design involves, analysis and testing. The more closely analysis and testing simulate the real situation, the more confidence one can have in the results. To limit the extend and the consequences of such failures more fundamental understanding how fatigue crack develop, in particular under dynamic loading is required. Over the years, a number of fatigue life prediction models have been established. No doubt, these models show some promising results for predicting fatigue of engineering components and structures subjected to constant amplitude, however, they are not reliable for life prediction of components and structures subjected to variable amplitude loading. Therefore, a robust life prediction mathematical model has yet to be developed. In reality, dynamic structural interactions, which create conditions for fatigue crack growth occurs. To understand such behaviour, comprehensive studies have to be performed. Many experimental and theoretical work have been published which relates to the investigations of cracked structure subjected to various dynamic conditions. However, these works were mainly carried out assuming that the cracks remain stationary. Dynamic interactions due to a growing fatigue crack have not been studied extensively. To understand the dynamic interactions due to a growing crack which lacks robust analytical models, extensive experimental work has to be performed. Due to the restrictions of conducting realistic fatigue tests on conventional fatigue- testing machines, a new fatigue-testing rig has been developed and is presented in this thesis. This device comprised of two based excited oscillators situated at the top and bottom of a bending specimen and being excited by an electro-dynamic shaker. The main operating principle of the rig is that inertial forces generated by the oscillators act on the specimen. By changing the natural frequency of the oscillators, the extent of the pre-load, and the pattern of the excitation, the rig provides a new and robust means of fatigue testing. A mathematical model that allows to investigate the dynamics of the system under a propagating crack has been developed for the new fatigue-testing rig. The system responses have been examined using standard nonlinear dynamics tools such as Poincare maps and bifurcation diagrams. Finally, an extensive experimental work has been conducted on the prototype fatigue rig to confirm it's capability of inducing fatigue crack in the specimen as well as to examine the system behaviour during harmonic and chaotic excitations.

Penetration of metallic targets by long rod projectiles is one of the basic research issues of terminal ballistics and impact dynamics. This work contributes to this field through theoretical and numerical investigations of the penetration performance of long rod projectiles, including both monolithic-rod and segmented-rod projectiles, into semi-infinite metallic targets.University of Manchester.

No description available.

No description available.

No description available.

No description available.

Le Liban se caractérise par ses hautes montagnes fortement urbanisées. Traversé par plusieurs failles principales et secondaires, ce pays présente de forts risques sismiques. Il a déjà subi plusieurs tremblements de terre destructeurs. Dans le futur, on craint un tremblement de terre majeur. Face à une telle situation, il est nécessaire de mener des travaux de recherche pour analyser ce risque. Ce travail de thèse s’inscrit dans ce cadre. Le travail est réalisé à l’aide d’une modélisation numérique avancée fondée sur la méthode des éléments distincts. Les études ont été effectuées à l’aide du code de calcul (UDEC). Les analyses sont établies sur des cas réels identifiés à partir de plusieurs visites de terrain. Un travail important a été aussi consacré à la collecte des informations relatives aux propriétés mécaniques des matériaux. La première partie de la thèse est consacrée à une synthèse bibliographique en rappelant les paramètres qui caractérisent la géométrie des discontinuités des massifs rocheux et leur comportement mécanique en compression et en cisaillement. Des méthodes d’analyse de la stabilité des milieux rocheux fissurés et quelques exemples réels publiés dans la littérature sont exposés. La seconde partie comporte des analyses sismiques menées sur un massif du site de Jezzine au Liban Sud. Les modélisations traitent différentes configurations : massif sans fractures, massif avec fractures horizontales et massif avec un réseau de fractures horizontales et verticales. On présente également les résultats obtenus avec un renforcement du massif par ancrage. La dernière partie présente une étude de l’influence de la présence de l’eau sur le comportement sismique des massifs rocheux. / Lebanon is characterized by high-urbanized mountains, which could be subjected to severe earthquakes, because of the presence of a major fault and some secondary faults. Lebanon was previously subjected to several destructive earthquakes, particularly in 551, 1202, 1759 and 1837 and more recently in the years 1956 and 2008. Experts predict a major seismic event in the future. Prevention constitutes an efficient way to minimize the earthquake consequences (casualties and property damage). This thesis aims to develop a methodological approach for the seismic stability of fractured rocks and to apply this methodology to the analysis of real case in Lebanon. The work is based on an advanced numerical modeling using the UDEC software to analyze the behavior of massive fractured rocks under seismic loading, taking into account the presence of water in the fractures. Due to lack of field data, significant work has also been devoted to the collection of data collection related to mechanical properties of the materials and joints. The first part of the thesis presents a literature review of the characterization of the rock discontinuities and methods used for the analysis of the stability of fractured rock masses. The second part presents seismic analysis of a real case in South Lebanon (Jezzine). Numerical calculations were carried on different configurations: rock mass without fractures, rock mass with horizontal fractures and rock mass with both horizontal and vertical fractures. Analysis was also conducted on the use of anchors for the rock mass stabilization. The last part presents a study of the influence of the presence of water on the seismic behavior of fractured rock masses.