Local Cooling during Welding: Prediction and Control of Residual Stresses and Buckling Distortion

Local Cooling during Welding: Prediction and Control of Residual Stresses and Buckling Distortion

Van der Aa, E.M.

Richardson, I.M. (promotor)

Mechanical Maritime and Materials Engineering

2007-06-19

One of the major problems during welding of thin plate structures is the occurrence of buckling distortion. This type of distortion is caused by the formation of compressive welding stresses; when these stresses exceed a certain critical stress level, the structure will buckle. Most methods for eliminating the welding induced buckling distortion, aim at a reduction of the tensile stresses around the weld, which leads to a reduction of the compressive stresses to a level below the critical level. Several techniques have been proposed in the literature to reduce or even eliminate buckling distortion. A number of these, referred to as Low Stress No Distortion (LSND) welding techniques, uses additional heating and/or cooling sources, which are applied during welding. One specific technique, referred to as Dynamically Controlled Low Stress No Distortion (DC-LSND) welding, was introduced by Guan et al. in 1993 and uses a localised cooling source, which trails the welding heat source at a short distance. Although the results produced are promising, the stress reduction mechanisms are still not fully understood. In this work, the three main fields of interest for the DC-LSND welding process, namely the thermal field, the residual stress field, and the buckling distortion, were investigated by means of conceptual, analytical and finite element models, and by experimental techniques, including thermocouple measurements, (synchrotron) X-ray residual stress measurements, residual deformation measurements, and microstructural evaluation. The combination of modelling and experimental work has provided valuable insight into the process of welding with a trailing heat sink. The mechanisms of DC-LSND welding were clearly explained by a conceptual five bar model, which is an extension of the three-bar model commonly used to describe the longitudinal residual stress development in welding. This model also defined the most important cooling source properties, i.e. the cooling source size with respect to the welding temperature field, the cooling source position with respect to the heating source, and the cooling source heat transfer coefficient.

welding
residual stress
deformation
buckling
finite element modelling
thermal modelling
synchrotron
x-ray
steel

http://resolver.tudelft.nl/uuid:65f45557-a4b6-430d-9774-14c9dbc17480

978-90-77172-29-2

Institutional Repository

doctoral thesis

(c) 2007 E.M. van der Aa