PSI - Issue 57

Cheng Huang et al. / Procedia Structural Integrity 57 (2024) 42–52 Cheng Huang et al./ Structural Integrity Procedia 00 (2023) 000 – 000

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cycles until the occurrence of fracture. On the other hand, to develop S - N diagrams, the specimens were fatigue-loaded until fracture or two million cycles; the latter is considered as an infinite life (i.e. run-out). Note that a subset of the test data were used in the development of both the CLDs and S - N diagrams, as shown in Table 2, where the test results, including the number of fatigue cycles, failure location and reason for test termination, are also presented. It can be seen from Table 2 that the majority of the coupons fractured within their parallel lengths, with fatigue cracks initiating from the edges, as illustrated in Fig. 4. Exceptions to this included as-built coupons F-AB-6, F-AB-10 and F-AB-11, where fatigue fracture occurred within the fillet or grip regions, and as-built coupons F-AB-4 and F-AB-14, where fatigue cracks initiated from the undulating surfaces, as well as a machined coupon F-M-2, where fatigue cracks originated from an internal pore. Note that, for the coupons (F-AB-6, F-AB-10 and F-AB-11) that fractured outside their parallel lengths, the results of the tests performed at the final (highest) stress levels (shown in Table 2) are excluded in the fatigue analyses in Sections 3 and 4.

F-AB-1

F-AB-4

Crack initiated from edge

Crack initiated from surface

Fig. 4. Typical fractured as-built coupons and fracture surfaces.

Table 2 Summary of fatigue test results. Test ID Coupon R

Stress range (MPa)

Number of cycles 273454 2000000 2000000 2000000 2000000 2000000 2000000 2000000 533440 2000000 2000000 296722 2000000 2000000 2000000

Crack initiation region/failure location

Reason for termination

Use of data

1 2 3 4 5 6 7 8 9

F-AB-1 F-AB-2 F-AB-2 F-AB-2 F-AB-2 F-AB-2 F-AB-2 F-AB-2 F-AB-2 F-AB-3 F-AB-3 F-AB-3 F-AB-4 F-AB-4 F-AB-4

0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.2

180 100 110 120 130 140 160 180 190 160 170 180 130 140 150

Edge/near one end within parallel length

Fracture Run-out Run-out Run-out Run-out Run-out Run-out Run-out Fracture Run-out Run-out Fracture Run-out Run-out Run-out

CLDs/ S - N diagrams

— — — — — — —

CLDs CLDs CLDs CLDs CLDs CLDs

CLDs/ S - N diagrams CLDs/ S - N diagrams

Edge/near one end within parallel length

10 11 12 13 14 15

— —

CLDs

CLDs/ S - N diagrams CLDs/ S - N diagrams

Edge/near one end within parallel length

— — —

CLDs CLDs CLDs