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Analysis Of Residual Stresses And Distortions In Circumferentially Welded Thin-Walled Cylinders

Qureshi, Muhammad Ejaz (2008) Analysis Of Residual Stresses And Distortions In Circumferentially Welded Thin-Walled Cylinders. PhD thesis, National University of Sciences & Technology, Rawalpindi.

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Abstract

Welding is a major joining technique employed in hi-tech industries like in nuclear, aerospace and aeronautical, submarine and shipbuilding and pressure vessel applications for the production of high performing resilient structures. The problems of weld induced imperfections like residual stresses and shape change behavior evolve almost simultaneously with the introduction of welding as a joining method and harmful stresses in metals due to welding were reported in 1892 by Slavianov in his work. Tremendous efforts were made in the last couple of decades showing remarkable development in new welding technologies for defect free resilient structures capable of excellent in-service thermal and structural load bearing features. Despite these considerable technological innovations in high temperature joining technologies, the problems of weld induced imperfections like residual stresses and distortions is still a major challenge for the welding engineers due to the complex nature of the welding phenomenon. Thin cylindrical shell structures constitute an important class of axis-symmetric structures and are exceptionally utilized in most of the high-tech domains. Therefore, the reliability of materials and structures in the form of thin-walled cylindrical structures is of paramount importance in aerospace, marine, aeronautical structures, pressure vessels and nuclear engineering applications. A number of longitudinal and circumferential welds are the mandatory integrating technique available for hi-tech applications like missile casing, nuclear reactors and pressure vessels, where specific strength and cost effectiveness are the major design constraints. These welds are commonly produced by single or double "V" joint configuration penetrations and single or multiple runs arc welding processes. Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW) process are the obvious selection in this regards due to excellent weld joint features. Low alloy steels (may or may not requiring post weld strengthening heat treatments depending upon the in-service loadings) along with stainless steels are the potential candidate materials. Transient temperature distributions during Gas Tungsten Arc Welding (GTAW) process and subsequent cooling of the weldments have significant effect on the microstructures, physical properties, residual stress distributions and development of weld solidification cracks. The primary driving forces for most of the weld induced imperfections are the transient temperature distributions followed by transient and residual stress fields. In the present research dissertation, transient temperature distributions, transient/residual stress fields and distortion patterns for circumferentially welded thin-walled cylinders of low carbon steel and stainless are investigated in detail. A hybrid numerical simulation and experimental based analysis approach is employed. The simulations strategy is developed and implemented by using commercial available general purpose finite element software ANSYS� enhanced with a number of author written subroutines. The moving heat sources, material deposition, temperature dependent material properties, metal plasticity and elasticity, transient heat transfer and mechanical analyses are included. One-way thermo-mechanical coupling is assumed i.e. de-coupled thermo-mechanical analysis in which the thermal analysis is completed first, followed by a separate mechanical analysis based on the thermal history. As part of an integrated effort to model and predict GTA welding process, a series of single-pass experiments for butt-joint configurations in thin-walled cylinders is conducted on robotized tungsten inert gas welding equipment. This dissertation therefore, presents the development of an experimental and numerical approach to the analysis of circumferentially arc welded thin-walled cylinders. The investigation jointly relies on the finite element analysis and the experimentation and shows a good co-relation between the simulation and experimental work with close agreement to the previously published literature (where applicable and cited).

Item Type:Thesis (PhD)
Uncontrolled Keywords:Analysis, Residual, Stresses, Distortions, Circumferentially, Welded, Thin-Walled, Cylinders, Slavianov, thermal, imperfections, transient
Subjects:Engineering & Technology (e) > Engineering(e1) > Mechanical engineering(e1.20)
ID Code:5967
Deposited By:Mr. Javed Memon
Deposited On:30 Jan 2011 18:59
Last Modified:30 Jan 2011 18:59

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