PSI - Issue 17

Lise Sandnes et al. / Procedia Structural Integrity 17 (2019) 632–642 L. Sandnes et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 2. Sketch showing the location and labelling of the different specimens used for metallographic examination (yellow) and tensile testing (blue) referred to the start position of the weld.

2.2. Metallographic examination

After the butt welding operation, one cross-sectional sample was cut from the end of the weld plate, as illustrated in Fig. 2, and made ready for metallographic examination using standard preparation techniques. In the present paper, only the results from the transverse hardness measurements at the end-position of weld are included. Additional optical images of the joint transverse macrostructure at different positions along the joint line are given in Part I (Sandnes et al. , 2019). The hardness measurements were made in accordance to ASTM standard E92-16, using a Mitutoyo Micro Vickers hardness testing machine applying a constant load of 1 kg. The distance between each indentation was 0.5 mm. In total, three independent test series were carried out along the specimen horizontal mid-section. Finally, the base material hardness was established from twenty individual measurements being randomly taken on one separate specimen of the base plate. Table 3. Overview of the specimens used for tensile testing. Included in the table are both their location and thickness, as well as the labelling and number of specimens tested. Note that the labelling is in accordance with that used in Fig. 2.

Weld zone tested Extrusion zone

Specimen thickness (mm) Labelling Number of specimens tested

EZ

2

A, B, C

3 3 3 3 3

EZ red

1.8

H, I, J

Heat affected zone HAZ

2

G, K, L M, N, O D, E, F

HAZ red

1.8

Base material

BM

2

2.3. Tensile testing

Two sets of tensile specimens were prepared for testing; one set having the original extrusion thickness of 2 mm, and another set having a reduced specimen thickness of 1.8 mm to remove the previously mentioned root defects due to “kissing” bond formation. For each specimen type, dual sets of tensile specimens were prepared. They have their center located either in the EZ or the HAZ on the retreating side (RS) of the weld. For the BM only 2 mm thick transverse tensile specimens were prepared for comparison with the weld samples. An overview of the specimen location, labelling and number of specimens being tested is given in Fig. 2 and Table 3. The tensile testing was performed in accordance with ASTM standard E8/E8M-16a, using a MST Criterion electromechanical test machine (5 kN load cell) with a fixed cross-head speed of 0.3 mm/min. However, because of the limited extrusion profile dimensions, the subsize specimens used had a reduced section length and width of 18 and 4 mm, respectively and a total length of 64 mm, which is outside the standard specifications. This resulted in a grip section width and gauge length of 10 mm. Note that the short gauge length will affect the measured values for the