PSI - Issue 2_A

Haydar Dirik et al. / Procedia Structural Integrity 2 (2016) 3073–3080

3078

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Haydar Dirik and Tuncay Yalçinkaya / Structural Integrity Procedia 00 (2016) 000–000

σ ol

m cycle

σ max n cycle

n cycle

σ ol

m cycle

σ max

σ min

Stress [MPa ]

σ ul

σ min

Stress [MPa ]

a b Fig. 3. Schematic representation of one block of loading spectrum used in analysis a) OL spectrum b) OL-UL spectrum.

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Nasgro XFEM Test Data

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60

σ min = 3.45 MPa σ max = 68.95 MPa n=1 CAL

50

40

30

Crack Length [mm]

20

10

0

0

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8

Number of Cycle

x 10 4

Fig. 4. Comparison of NASGRO, XFEM and Porter test data for CAL.

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Nasgro XFEM Test Data

Nasgro XFEM Test Data

70

60

60

50

σ min = 3.45 MPa σ max = 68.95 MPa σ ol = 103.43 MPa m=29, n=1

σ min = 3.45 MPa σ max = 68.95 MPa σ ol = 76.54 MPa m=29, n=1

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Crack Length [mm]

Crack Length [mm]

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10 12 14 16 18 x 10 4

Number of Cycle

Number of Cycle

x 10 4

Fig. 5. Comparison of NASGRO, XFEM and Porter test data for di ff erent OL level.

Figure 5 shows comparisons of predicted values by NASGRO, XFEM and Porter test data under di ff erent OL ratio for spectrum defined in Figure 3a, and Figure 6 illustrates comparisons under same OL ratio but for di ff erent OL spacing for spectrum defined in Figure 3a. Figure 7 presents the results for OL-UL spectrum defined in Figure 3b at di ff erent load ratios. Predicted values by XFEM are in good agreement with NASGRO and test data. Retardation e ff ects of OL can be seen by comparing Figure 4 and Figure 5. It is obvious that neglecting the e ff ect of load sequence in fatigue calculations under VAL can lead to completely invalid life predictions. Figure 8 shows simulation results