PSI - Issue 71

Shreebanta Kumar Jena et al. / Procedia Structural Integrity 71 (2025) 103–110

105

3. Test details Present tests have been performed under remote axial and torsional strain-controlled loading conditions with phase shift angles of 0 ° and 90 ° at ambient conditions ( ~ 28 ° C) in the air environment following ASTM E2207-08 (2009). The axial and torsional strains have been controlled using an axial-torsion extensometer. Remote triangular strain waveforms have been applied in a completely reversible way. During the test, localized surface strains have been recorded using DIC for two complete cycles at regular cycle intervals (typically after 50-100 cycles). This system has also been used for capturing the fatigue crack initiation event precisely . 3.1. Remote loading conditions The axial and torsional strain amplitudes have been adjusted to get intended remote equivalent strain amplitude (Eq. 1). The Shear to Axial Ratio (SAR: the ratio of remote shear strain to axial strain amplitudes, given by Eq. 2) has been set as 1. The in-phase (or proportional) and 90 ° out-of-phase (or non-proportional) axial torsion tests have been conducted with remote equivalent strain amplitudes of 0.1% and 0.075%. Typical remote strain paths are shown in Fig. 3. The corresponding axial and shear strain amplitudes for these equivalent strain amplitudes have been given in Table 1. = √ ( ) 2 +( / √ 3) 2 Where, , and are the equivalent, axial and shear strain amplitude respectively SAR = ( √3 × ) Eq. 2 In this table, the equivalent strain amplitude (Eq. 1) belongs to a remote controlled field for tubes with holes, however, equivalent strain amplitude was applied uniformly for tube without hole on the same grade of material Arora et al. (2016). Table 1. Details of hole diameter, applied remote strains, phase shift angle and test fatigue life Test Fig. 2. Schematic of test specimen used for remote proportional/ non-proportional axial-torsion tests Eq. 1

Hole diameter (mm) (%) (%) (%)

Test fatigue crack initiation life (N i ) (Number of cycles)

Phase shift angle ( ° ) 0

studies on SA 333 Gr. 6 (present/ reported) Tube with hole (present)

Ni corresponds to

Test ID

CN5p5_IAS_rE_10 CN5p5_OAS_rE_10 CN5p5_IAS_rE_7p5 CN5p5_OAS_rE_7p5 CN8_IAS_rE_10 CN8_OAS_rE_10

0.0707 0.1225 0.0707 0.1225 0.0530 0.0919 0.0530 0.0919 0.0707 0.1225 0.0707 0.1225

1283 6484 4349 76996

0.100

90

5.5

1mm crack size using DIC Earlier of 1mm crack size or 25% load/ torque drop

0

0.075

90

0

902 5875 4672 2001 1594 1157

8

0.100

90

Tube without hole [2016]

CA35S61p0 CA35S61p90 CA53S92p0 CA53S92p90

0.35 0.61 0.5

0

0.35 0.61 0.5 90 0.53 0.92 0.75 0 0.53 0.92 0.75 90

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