Seam tracking based on estimation of weld position using Kalman filtering

Abstract

A seam tracking method is presented based on the estimation of weld position during the gas tungsten arc welding process. Kalman filtering of the weld pool images from a visual sensor is applied to compute recursively the solution to the weld position equations which are established based on an estimation of the centroid position of the weld pool images. This centroid, the position of which corresponds with the weld position, is extracted as the measurement eigenvector. The evolution of the weld position data from the weld pool images can be described through an appropriate process model, so that the weld position can be detected by applying a Kalman filter. This allows adjustment of the welding torch position in real time, which may significantly reduce processing time and promote seam tracking accuracy. Simulations and actual welding experiments have demonstrated the effectiveness of the proposed algorithm in the presence of weld pool image noise and have demonstrated the robustness of weld position detection for seam tracking.     

Three-dimensional upper bound limit analysis of underground cavities using nonlinear Baker failure criterion

A generalized nonlinear Baker failure criterion is employed with the upper bound limit analysis to study the surrounding rock stability of underground cavities. A three-dimensional (3D) failure mode is established by extending the two-dimensional (2D) failure mode, which offers an upper bound expression of the surrounding rock pressure. This method is validated with a series of examples before the influence of four parameters of scale parameter, curvature parameter, shift parameter and lateral pressure coefficient, on the surrounding rock pressure is analyzed. According to these results, failure ranges of the underground cavities are determined. The following conclusions are reached: (1) the proposed approach is more accurate to predict surrounding rock pressure than the Mohr−Coulomb failure criterion; (2) the surrounding rock with large scale parameter, curvature parameter, shift parameter, and lateral pressure coefficient can lead to a more stable underground cavity; (3) the failure range in 3D mode can be predicted according to the upper bound solutions.     

Determination of lower bound fracture toughness of a high strength low alloy steel welded joint

Abstract

The use of high strength low alloy steels for high performance structures (e.g. pressure vessels and pipelines) requires high strength consumables to produce an overmatched welded joint. This globally overmatched multipass welded joint contains two significantly different microstructures, as-welded and reheated. In this paper, the influence of weld metal microstructure on fracture behaviour is estimated in comparison with the fracture behaviour of composite microstructures (as-welded and reheated). The lower bound of fracture toughness for different microstructures was evaluated by using the modified Weibull distribution. The results, obtained using specimens with crack front through the thickness, indicated low fracture toughness, caused by strength mismatching interaction along the crack front. In the case of through thickness specimens, at least one local brittle microstructure is incorporated in the process zone at the vicinity of the crack tip. Hence, unstable fracture occurred with small, or without, stable crack propagation. Despite the fact that the differences between the impact toughness of a weld metal and the that of base metal are insignificant, the fracture toughness of a weld metal can be significantly lower.