PSI - Issue 71

Sudarshan Solanki et al. / Procedia Structural Integrity 71 (2025) 95–102

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Table 3. Maximum peak equivalent strain amplitude gradient (linearized) along axial and radial directions for both loading cases with 1% peak equivalent strain amplitude.

Maximum value of linearized strain gradient along radial direction (%/ ) 0.016 (Axial location: mid-region of SS-base)

Maximum value of linearized strain gradient along axial direction (%/ ) 0.038 (spread from SS-base to LAS-base)

Loading case

Pure axial

1.658 (at SS-base & SS-weld juncture)

0.163 (Axial location: near fusion line in SS-base)

Pure torsion

5.2. Predicted fatigue life The number of cycles to fatigue crack initiation viz. crack initiation life was predicted by taking localized peak equivalent strain amplitudes and using region/ material specific strain life curve equations (Murthy et al. (2022), Chaturvedi’s ( 2013), Interim reports (2022)) From a fatigue life perspective, the base metal SS304LN is most susceptible to failure in cyclic loading under higher peak equivalent strain amplitude. Hence, the fatigue crack is likely to initiate from SS base region for higher strain amplitudes (0.75% and 1%) and SS weld region for lower peak strain amplitudes (0.35% and 0.5%) as outlined in Table 4 based on minimum fatigue life criterion.

Table 4. Estimated cycles to failure for pure axial and pure torsion condition in different regions.

̅ (%)

Pure axial

Pure torsion

Materials ( → )

Region with minimum fatigue life

Region with minimum fatigue life

LAS base

SS base

SS weld LAS base

SS base SS weld

1% ̅(%) Np 0.75% ̅(%) Np 0.5% ̅(%) Np 0.35% ̅(%) Np

1.010

0.339 1618 0.259 2128 0.123 3383

0.289 8318 0.255 10007 0.205 13090 0.1643 16208

1.040

0.277 2001 0.185 2741 0.081 3908 0.024 4742

0.307 7559 0.272 9147 0.225 11746 0.184

SS Base

SS Base

766

709

0.744 1720 0.509 4960 0.351 15000

0.747 1704 0.507 5022 0.351 15030

SS Base

SS Base

SS Weld

SS Weld

0.0387

6. Conclusions The salient outcomes from analyses carried out on SA508(base-1)-SS308L(weld)-SS304LN (base-2) Dissimilar Metal Welds (DMWs) under remote pure axial and pure torsion cyclic loading conditions, are summarized below: ● For pure axial loading conditions, the higher strain gradient exists along the axial direction. However, along the radial direction, strain gradient is very small. The maximum value of strain amplitude occurs in the SS304LN region. ● For pure torsion loading condition, the strain gradient is steeper at dissimilar material juncture along axial direction than that of radial direction. The maximum value of strain amplitude occurs at the outer surface in the SS304LN region. ● The maximum strain gradient is significantly steeper for the pure torsional case than that of the corresponding pure axial case. 14627 Np : predicted fatigue crack initiation life, ̅ : localized equivalent strain amplitude, ̅ : peak equivalent strain amplitude SS Weld SS Weld 4508