AN ANALYTICAL INTERPRETATION OF WELDING LINEAR HEAT INPUT FOR 2D RESIDUAL STRESS MODELS

摘要

Welding residual stress simulation using finite element analysis has become increasingly common in supporting fitness-for-service assessment. Two dimensional (2D) cross-section models, such as using generalized plane strain assumptions for linear welds in plate structures and axisymmetric assumptions for piping and vessel girth welds are typically used due to their computational efficiency and simplicity in data reduction process, especially for performing a large amount of parametric analyses. However, there seem no consistent procedures in place for translating actual weld linear heat input used in practice to a 2D cross-section model in which heat loss in welding travel direction is unaccounted for, often resulting in overheating to a significant degree if actual welding heat input is used. This paper starts with the introduction of a two-part analytical linear heat input representation for a simplified 2D weld residual stress modeling procedure in which weld metal is deposited at a preset temperature such as melting with a hold time. The first part is based on a simple thermodynamics concept, which describes the heat required for elevating a weld pass from room temperature to deposition temperature. The second part is based on an equivalent transient heat transfer solution that measures the amount of heat needed to sustain deposit temperature during hold time. With this proposed method, linear heat input involved in a 2D residual stress model can be inferred for relating to actual welding conditions, typically specified in terms of current, voltage, and welding speed. By the same token, for a given set of welding parameters, welding heat flow modeling procedure involved in a 2D FE residual stress model can be consistently defined in terms of deposit temperature and hold time. A number of validation case studies are presented and the results have showed that the proposed procedure provides an effective means for inter-relating actual welding linear heat input and heat content associated with 2D residual stress models.