Showing papers by "Paul A. Colegrove published in 2012"

Effect of high pressure rolling on weld-induced residual stresses

Abstract: The formation of large residual stresses continues to be a problematic side effect of all common welding processes. In this work, localised high pressure rolling of gas metal arc welds to relieve these residual stresses has been investigated using strain gauging and neutron diffraction. Rolling was found to remove undesirable tensile stresses and even induce large compressive ones, though only when applied after rather than during welding. Strain measurements taken during combined welding and rolling operations show that this is because material at the weld line continues to yield as it cools. This erases any beneficial effect on the stress distribution of rolling at high temperature. A method of rolling using an oscillating force is also presented and found to be just as effective as the equivalent static force process.

Residual strain measurement for arc welding and localised high-pressure rolling using resistance strain gauges and neutron diffraction:

Abstract: Neutron diffraction and foil resistance strain gauges have been used to study the state of residual stress introduced by localised high-pressure rolling of structural steel plates, and compare it to that caused by gas metal arc welding. Rolling creates a region in which the residual stress state is highly compressive in the rolling direction. Furthermore, this region is sharply defined, making it potentially very suitable for cancelling out the tensile residual stresses caused by welding. It is also demonstrated that non-destructive strain measurements made during the welding and rolling processes can be used to indicate residual elastic strain and stress, and that this method shows good agreement with conventional neutron diffraction measurements. Determination of residual stresses in this way requires consideration of the effect of curvature on the values of strain measured at the surface of the object.

Added Layer Manufacture

Abstract: A method of producing a 3D article by additive-layer manufacture is provided. The method includes the steps of: depositing and fusing a layer of material on a substrate or on a previously fused layer of material; and repeating the depositing and fusing step to build up successive layers of material, and thereby produce the 3D article. The method further includes performing one or more times the step of: plastically deforming under compressive loading the most recently fused layer before the next repeat of the depositing step by contacting a loading head to the most recently fused layer and moving the loading head thereover while maintaining the contact. In the deforming step, the most recently fused layer at the loading head is preferably constrained from deforming laterally. The loading head may deform the most recently fused layer when that layer has cooled significantly.