Issue 48

M. Tirenifi et alii, Frattura ed Integrità Strutturale, 48 (2019) 357-369; DOI: 10.3221/IGF-ESIS.48.34 358 I NTRODUCTION he processes of welding induce modifications of microstructure, constraints, and deformations residual, which it is as much difficult to control. High residual stresses combined with the presence of hard phases can lead, with the embrittlement of the joint or, the distortions induced by a welding can induce misalignments of the parts making impossible the realization of a sequence of welding. The numerical simulation of the processes of welding very often appears as a means of privileged access to the sizes, which characterize them. Thus, the numerical simulation of welding is greater interest when it is a question of studying the mechanical resistance of a welded joint or to check the feasibility of a sequence of welding. The resistance of the welded joints does not depend only on the properties of the base metal and the filler metal employed, but also of the presence of geometrical defects of surface or internal defects (blowholes, lacks of penetration). Numerical modeling supports more and more in practice as respects design. The use of the powerful computers and the effective software can provide the valid results, which are used to increase reliability in the structural design [1-6]. The complex mathematical procedures take account of physical and geometrical non-linearities of the structure [7]. An important tool for mathematical modeling is in particular the finite element method [8]. The analysis of the constraints in the welding also had the considerable attention in the past. In [9], he was defined the stress intensity factor of the joint welded for typical structures, inter alia for a fillet weld. Lazzarin [10] discuss derivation of the stress intensity factor for the welded joints, they described distributions of the constraints in the vicinity of the edges of the welding. An exact solution on the analysis of the constraints of the fillet welds was described by Dawei [11]. To study the distribution of the temperature, a research was made by Guedes [12], he carried out an experimental study and numerical with respect to the fillet weld. Eight points were selected for measurements with three distances 15, 25 and 35 mm, starting from the line of fusion; the eight points were selected on each side of the upper surface of the plates. He traced the longitudinal distribution of residual stress in the plate. He was observed an increase in the residual stresses abruptly equal to the yield stress close to the welding, and the longitudinal residual stresses decrease abruptly starting from the welding and become compressive in the areas beside the welding. There are very small compressive forces in the transverse edges of the plate. According to the finite element calculations of Kenno and Park [13, 14], the distributions are similar while they observed that the thinner plate has slightly smaller tensile stress and slightly bigger compressive stress. The measurement of residual stress in welded plates requires costly equipment and qualified technicians. Thus, many researchers use an idealized model to represent the residual stress distributed in a plate instead [15, 16, 17], Applying the idealized model in the studied plate. In thermal analysis, the heat input during the welding process was applied on the specimen using the moving volumetric heat flux in the numerical model. In the investigation that was developed by Goldak [18], for the T-joint weld, welding was performed via single-side welding with an angle θ= 45°. The front and rear density distributions of the volumetric heat flux for the T-joint welding were governed by Eqs. (1)-(2), respectively. 2 2 2 2 2 2 6. 3. . . 3 3 3 ( , , ) exp . . . f f f f f Q X Y Z q x y z a b c a b c                (1) 2 2 2 2 2 2 6. 3. . . 3 3 3 ( , , ) exp . . . r r r r f Q X Y Z q x y z a b c a b c              (2) where 0 ( ) X x x t     , 0 0 ( )cos ( )sin Y y y z z       and 0 0 ( )sin ( )cos Z y y z z        , (x0, y0, z0) is the position of the point where the torch is aimed in the (x, y, z) coordinate system, Q is the power input, η represents the welding efficiency, where 0.85 is employed in the study of Kemppi [19], ν is welding velocity, t is the transient time, and the parameters a f , a r , b and c refer to the geometry of the heat source for the welding being modeled. The f f and f r , represent the front and rear heat apportionment of heat flux, where 2 ( ) f f f r f a a a   and 2 / ( ) r r f r f a a a   are assumed by Estefen [20], respectively. Furthermore, an experimentally validated numerical model was created by Hibbit [21], to investigate the residual stresses and the distortions in a T-joint welding using Abaqus, the differences between the numerical and experimental results are acceptable. In the fusion zone and its adjacent region, the numerical simulation of longitudinal residual stress shows good agreement with the experimental measurements. The disagreement between the numerical simulation and experimental T