**1. Introduction**

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Due to the nature of welding process involving localized heat generation from moving heat source (s), rapid heating in the welded structures, and subsequent rapid cooling, problems such as residual stresses and distortions of welded structures remain great challenges to welding practitioners, designers and modeler. From modeling point of view, it will be very useful if the parameters of interest which contribute to the residual stresses and distortions in various types of welded joint and structure application can be simulated numerically so that welding performance with respect to the various aspects could be assessed and evaluated in an efficient manner (Goldak & Akhlagi, 2005; Lindgren, 2006; and Zacharia et al., 1995). Thorough consideration and assessment of the welding quality could then also be performed in earlier stage in a virtual environment. Moreover, dimensional inaccuracies due to the welding deformation giving rise problems in subsequent assembly and fabrication processes could also be predicted along with the necessary justification needed.

In recent years, various aspects and interests in the numerical modeling of welding residual stresses and distortions, mostly using finite element method, have been elaborated by researchers. Teng & Lin (1998) predicted the residual stresses during one-pass arc welding in steel plate using ANSYS software and discussed the effects of travel speed, specimen size, external mechanical constraints and preheating on the residual stresses. Tsai et al. (1999) studied the distortion mechanisms and the effect of welding sequence on panel distortion and utilized 2D finite element model. Residual stresses and distortions in T-joint fillet welds with the effects of flange thickness, welding penetration depth and restraint condition of welding was simulated by Teng et al. (2001) using thermal elasto-plastic finite element

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techniques. Further, effect of welding sequences on residual stresses of multi-pass buttwelds and circular patch welds was also investigated by Teng et al. (2003). Moreover, Chang & Lee (2009) performed the finite element analysis of the residual stresses in T-joint fillet welds made of similar and dissimilar steels.

3D Finite Element Simulation of T-Joint Fillet Weld:

Effect of Various Welding Sequences on the Residual Stresses and Distortions 585

**Figure 1.** Illustration of residual stress mechanism in welding (source: Masubuchi, 1980)

equal to one-half of tensile stress in the middle bar.

= 0) can be expressed by the following formulas:

Elastic and plastic strains:

*2.1.2. Residual stress due to uneven distribution of non-elastic strains* 

middle bar is restricted by other bars, compressive stress is encountered at the middle bar and the two side bars are subjected to opposite tensile stress. The compressive stress on middle bar, increases in linear elastic manner when it is heated (AB curve) until the yield stress of material in particular temperature reached, then plastic deformation is encountered which affects in decreasing compressive stress (BC curve). During cooling stage, the stress sign in middle bar is dramatically changed from compressive to tension stress and increases in linear elastic way (CD curve) up to the yield stress at point D. Then, non-linear plastic behaviour takes place (DE curve) in room temperature resulting in a tensile residual stress in the middle bar and contrary a compressive residual stress in both side bars which are

When a metal bar is subjected to a uniform heat, it produces a uniform expansion lead to no thermal stresses. However, when it is subjected to non-uniform heat as the case of welding, thermal stresses and strains will be formed. Residual stress field in plane stress condition (*σ*<sup>z</sup>

> *xx x yy y*

 

 

 

 

*xy xy xy*

, ,

.

(1)

The present study extends the previous work of Teng et al. (2001) and focuses on numerical simulation of welding sequence effect on temperature distribution, residual stresses and distortions of T-joint fillet welds. Several welding sequences were considered and the resulted distribution of welding temperature, longitudinal and transverse residual stresses and angular distortions were simulated utilizing three dimensional finite element models. Four welding sequences considered were one direction welding, contrary direction welding, welding from centre of one side and welding from centres of two sides. Further, a welding sequence producing the smallest residual stress, distortion as well as distortion difference between both flanges was then investigated. The numerical simulation was done in ANSYS environment.
