Support tools for the prediction of distortion in the design and manufacture of thin plate welded structures

Camilleri, Duncan

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Thesis

Support tools for the prediction of distortion in the design and manufacture of thin plate welded structures

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Creator

Camilleri, Duncan

Rights statement

Strathclyde Thesis Copyright

Awarding institution

University of Strathclyde

Date of award

2005

Thesis identifier

T11166

Qualification Level

Doctoral (Postgraduate)

Qualification Name

Doctor of Philosophy (PhD)

Department, School or Faculty

Department of Mechanical Engineering

Abstract

This study aims to develop and validate a wide-ranging simulation tool to predict welding distortion in plates and shells, with particular emphasis on out-of-plane deformation. The approach adopted in this thesis, uncouples the thermal, elasto- plastic and structural effects leading to distortion and makes use of simple algorithms, named ‘ Mismatched Thermal Strain ’ and ‘Contraction Thermal Strain These algorithms are generic with respect to material and welding process and they enable the application of finite element simulation and analysis on an economical and industrially practicable scale. The final computational based approach has been used to investigate alternative welding sequences in multiply stiffened plates, with respect to the minimization of out-of-plane deformation. The theoretical models and results generated in this study have been supported at all stages by welding tests of a realistic nature to maintain confidence in the validity and applicability of the treatments. To achieve this aim, a pilot programme was designed to develop thermal and distortion measurement techniques and computational approaches, before up-scaling to a typical industrial size of fabrication. Steel plates were butt and fillet welded in the pilot programme to give 0.5m square finished test plates, while plates of more realistic dimensions at 4m x 1.5m were welded, to act as a comparison and cross-reference for the large scale computational analysis. From the computational viewpoint, the problem has been reduced to a single load step analysis per weld pass. Comparison between the results of the simulations and the measured out-of-plane deformations was good. The accuracy of the computational analysis was found to depend on knowledge of the initial out-of-plane deformations and other external factors such as self-weight and support positions. In double-sided fillet welding using two-welding heads in parallel, insufficient spacing or staggering of the heads means that the contraction force could exceed the critical buckling load of the structure. In multiply stiffened plates, minimization of the out- of-plane deformation was achieved by welding the central stiffeners first followed by the adjacent outer stiffeners.

Advisor / supervisor