PSI - Issue 17

Ashu Garg et al. / Procedia Structural Integrity 17 (2019) 456–463

461

Ashu Garg et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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AS of joints. Since, material on the AS is of lower strength and high ductility (refer Fig. 2) than the material on the RS (AA7075), thus, tensile failure of sample was observed from the HAZ. Since, the HAZ region undergoes the thermal cycle without much strain induced plastic deformation and is typically softer than the neighboring TMAZ region. The localized necking and failure band at angle ~46° is noted from the experiment. The FE analysis with ductile damage model also unveiled the crack initiation and propagation through HAZ region from the AS of the workpiece (with localized necking and band at angle predicted as ~50°). FE predicted stress development for different element selected from high stress concentrated region of particular zones i.e. HAZ, TMAZ on AS, SZ and HAZ, TMAZ on RS are shown in Fig. 5 for FSW joints with both CYL and TIF tool pins. From Fig. 5(a) it is observed that the reasonably higher stresses are generated on element selected from TMAZ (AS) and SZ regions for the joint prepared with CYL tool pin. Joint failure is also observed from the interface of TMAZ and SZ during experiment. For TIF tool pin, higher stresses are generated on element selected from HAZ region on AS and joint also failed from the same region during loading. Moreover, comparing the stress distribution for CYL and TIF tool pin it may also be noted that element stresses rise for CYL tool pin is more sharp with less elongation at failure whereas for the joint with TIF tool pin, the rise is more gradual and exhibited higher elongation at failure (refer Fig. 5(b)).

100 150 200 250 300 350 400 450 Von Mises stress (MPa)

100 150 200 250 300 350 400 450 Von Mises stress (MPa)

HAZ (AA6061) TMAZ (AA6061) SZ TMAZ (AA7075) HAZ (AA7075)

HAZ (AA6061) TMAZ (AA6061) SZ TMAZ (AA7075) HAZ (AA7075)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 50

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 50

Displacement (mm)

Displacement (mm)

0.6

0.6

HAZ (AA6061) TMAZ (AA6061) SZ TMAZ (AA7075) HAZ (AA7075)

HAZ (AA6061) TMAZ (AA6061) SZ TMAZ (AA7075) HAZ (AA7075)

0.5

0.5

0.4

0.4

0.3

0.3

0.2

0.2

0.1

0.1 Plastic equialent strain

Plastic equivalent strain

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0.0

Displacement (mm)

Displacement

Crack propagation started through TMAZ

Crack initiation and propagation through HAZ

Crack initiation started

Necking in HAZ region

(a)

(b)

Fig. 5. Elemental stress and strain development after tensile testing of welded joints prepared with (a) CYL; (b) TIF tool pins.