PSI - Issue 5

Sameera Naib et al. / Procedia Structural Integrity 5 (2017) 1417–1424 Naib et al./ Structural Integrity Procedia 00 (2017) 000 – 000

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weld heterogeneity. This observation acts as a motivation for this paper to further investigate the validity of slip line theory in complex heterogeneous welds. Using a combination of experimental results and finite element analysis, plastic deformations are studied thoroughly and its effect on structural response is characterized. The applicability of slip line field theory in welds is also discussed.

2. Material and methods

25mm thick steel plates of grade S690QL have been prepared with a double V bevel and joined by metal active gas weld. Welding was performed using two different weld consumables, such that an undermatching (UM) region and an overmatching (OM) region were obtained within the connection. The strength mismatch with respect to the base metal (based on yield strength) was 1.24 in the OM region and 0.86 in the UM region. From this welded plate, a macrograph was extracted to perform hardness mapping (Fig. 1(a)) to characterize the heterogeneity present in the material (bearing in mind that hardness is closely related to ultimate tensile strength). Around 1200 Vickers hardness indentations were made with an indentation load of 5kgf (HV5) (Fig. 1(b)) . The hardness maps serve as an input to the numerical model explained in Section 2.1 . Two bars of 400mm length and 20mm width and thickness were extracted from the same welded plate for single edge notched tensile (SE(T)) testing. Detailed procedure of experimental testing to analyze slip lines is described in Section 2.2.

Over match

Base material

Under match

5mm

5mm

HV5

(a) (b) Figure 1: (a) Extracted specimen showing the weld region and (b) 2D contour plot of welded S690 structural steel with overmatching (OM) and undermatching (UM) configuration

The plot of weld traverses (Fig. 2) obtained from the UM and OM region clearly shows strong hardness variations at different locations. OM and UM weld metal clearly exhibit different hardness levels, involving levels of 280-350HV in the overmatching region and 180-225HV in the undermatching region. Also, hardened Heat Affected Zones (HAZ) are observed having a hardness around 400HV over a width of 2-3mm. The depicted hardness traverses indicate the weld’s suitability to analyze slip lines in extreme heterogeneous conditions.

2.1. SE(T) experiments

SE(T) experiments were performed on specimens extracted from the S690 welded plates. SE(T) bars were given a square cross section with W=B=20mm , and were sufficiently long to provide a grip daylight length L=200mm. Side grooves were applied to the specimens. The tests were performed on accordance with UGent’s in -house procedure for SE(T) testing (M. Verstraete et al., 2013). The tests were performed on a 1000kN universal test rig with the assistance of hydraulic clamping, specimen end rotations being inhibited. Two notch locations were considered: one specimen’s notch was placed in the OM region and the other specimen’s notch was placed in the UM region. Sharp notches were applied through saw cutting and had a tip radius of 0.075mm. CMOD and CTOD were measured using double clip