PSI - Issue 60

Rohan Nair et al. / Procedia Structural Integrity 60 (2024) 93–114 Rohan Nair / StructuralIntegrity Procedia 00 (2023) 000–000

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3.3.

Metallurgical analysis

Tensile properties were evaluated from WPS coupon and coupons heat treated along with test article as per ASTM E8 [11]. Micro-vickers hardness was evaluated with 50gf load in weld cross section to assess the quality of weld microstructure and presence of defects, if any. Macrostructure and microstructure was evaluated in welded test coupon by following standard metallographic procedure. Fractographic analysis was carried out using Field Emission Scanning Electron Microscope (FESEM) on WPS tensile tested specimen and burst tested test article. Fig. 13 shows the burst pressure tested test article with sample extraction plan for fractographic analysis. Samples cut from test article representing longitudinal and circumferential direction of crack generated during pressure test is analysed in FESEM.

Fig. 13: Photograph of burst tested AA6061 sector showing sample extraction plan for fractographic analysis. C1- circumferential crack, L1, L2 & L3 – longitudinal crack

4. Results and discussion

4.1.

Tensile, microstructure and micro-hardness The tensile test results of parent metal and weld are tabulated in Tables 5 and 6 respectively. Achieved tensile properties of parent material meets the specification requirement. Weld tensile specimens failed at heat affected zone (HAZ) and mechanical properties of all 12 specimens are meeting the specification, expect three specimens. 0.2%YS on three specimens was found to be 2-7 MPa lower than design value, as can be noted from Table-6. The lower 0.2% YS in three cirseam specimens (as per Table-6), could be due to minor local thickness variations in tensile specimens extracted from cirseam weld (between shell to IC ring).

Table 5: Tensile test results of heat treated coupons (Gauge length 50mm) Coupon Identification Nos. 0.2%Yield Strength Specification – 240 (MPa)

Ultimate Tensile Strength Specification – 280 (MPa)

% Elongation Specification-10

1

275

338

17.5