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UBC Theses and Dissertations

An investigation of deformations in stainless steel rings by heating Towfighi, Siyavash


Screen cylinders are widely used in the field of pulp and paper for the removal of oversized contaminants. These screens may consist of several cylindrical partitions that are attached to each other by welding them to cylindrical rings. Since they are subject to various types of loading and placed in a corrosive environment, it is desirable to understand the changes that occur in them as a result of heating in a welding process. The focus of this study is to identify the cause and magnitude of deformations due to welding in the connecting rings of stainless steel AISI 304L. This is accomplished by investigating two potential mechanisms: 1) Microstructural changes such as phase transformations, and 2) Plastic deformation. To consider microstructural changes, a ferritescope is utilized for detecting the non-austenitic phases that may occur. Measurements taken from connecting rings prior to and after welding show that little phase transformation is caused in AISI 304L. In a second set of experiments, cylindrical specimens of AISI 304L are heated to elevated temperatures and compressed in the Gleeble 3500 machine. It is confirmed that heating and straining produce insignificant phase transformations in the rings. Material data is also obtained for elevated temperature stress strain curves at low strain rates that were not available. These results are used in a thermostructural analysis of the rings for plastic deformation. A simplified constrained beam model is used to illustrate the possibility of compressive yielding in the heated region of the material. This analysis highlighted important aspects of the thermo-structural analysis including buckling/bending and the temperature profile. Experiments on square plates of AISI 304L confirmed some of these predictions. A finite element model created using LS-DYNA and C++ code predicted the deformations in square plate samples with reasonable accuracy. A simpler finite element methodology is then used as an extension of this work to examine plastic deformation in the AISI 304L rings after welding. About 440 simulations with varying parameters are performed with the results indicating that significant plastic deformation occurs during the welding procedure and suggestions are given for controlling this deformation.

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