Hull construction with composite materials for ships over 100 m in length

Thesis (Nav.E. and S.M. in Ocean Systems Management)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2002.Includes bibliographical references (leaves 124-132).The operational envelope of the maritime industry requires high performance marine vessels, which demand increased structural integrity and durability, coupled with significant weight reduction and minimization of cost. The design and fabrication of a "large vessel" by use of composite materials is within the current technology. However, a number of major technical and economic aspects are questionable. This study will examine the structural design for vessels longer than 100 m. It will also identify the major advantages and disadvantages of this composite structure compared with one made of steel, focusing on the technical and economic aspects. Material selection, fabrication methods and design concepts for composite structures, such as elimination of frames, will be explored and comparisons will be developed. The potential to significantly reduce or even eliminate the risk areas will be evaluated. Four different structural designs of a hull from composite materials are examined for a midship section of an existing naval ship (DDG51 type) and they are compared to the one built from steel. In order to select the best option of these structural designs, three variants are analyzed: structural configuration of composites, material option and fabrication process. Additionally, the effect of several critical areas, such as safety factors selection, present and future structural limitations, required fabrication experience, durability, complexity, infrastructure issues, and a cost and market analysis of using fiber reinforced plastic (FRP) in ship design and construction are included in this study. The proposed hull design combined with the optimum materials and fabrication method shows that a large ship is both technically and economically feasible.by Konstantinos Galanis.Nav.E.and S.M.in Ocean Systems Managemen

Fracture of aluminum naval structures

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007."June 2007."Includes bibliographical references (leaves 238-272).Structural catastrophic failure of naval vessels due to extreme loads such as underwater or air explosion, high velocity impact (torpedoes), or hydrodynamic loads (high speed vessels) is primarily caused by fracture. Traditionally, naval structures have been designed to resist yielding, buckling and fatigue, but not fracture. Consequently, adequate methods and procedures to design ships against fracture have not been developed. The rapidly increasing application of lightweight materials, such as aluminum alloys, in the shipbuilding industry requires fundamental understanding of mechanisms and mechanics of fracture that govern naval stiffened panels. Therefore, a comprehensive tool consisting of application of advanced fracture models, material calibration, and validation through component testing is provided that will increase the survivability envelope and speed up the development process of new vessels. Cracking is a major cause of structural degradation, which is a primary source of costly repair work on metal structures. This thesis studies the structural response of various stiffened plates and compares them with unstiffened plates represented by compact tension (CT) specimens.(cont.) An extensive experimental program is presented that includes coupon testing and small and intermediate scale tests on naval aluminum structures including a variety of monolithic T-type extruded and flatbar welded specimens. Representative naval designs are selected and subjected to quasi-static loading and a number of key parameters, such as geometry, loading rate and structural configuration are evaluated with respect to fracture. Numerical modeling and analyses of ductile fracture initiation and propagation on a pre-cracked geometry using a commercial finite element code (ABAQUS), taking into account the behavior of simple uncracked material, has been performed showing a very good agreement with small and intermediate scale tests. Two major contributions of this thesis are the mapping of crack patterns in stiffened plates and the development of a methodology which enables ship designers to evaluate critical areas within a structure with respect to crack initiation, propagation, optimum material usage, and computational cost.by Konstantinos P. Galanis.Ph.D