PSI - Issue 39

Szymon Derda et al. / Procedia Structural Integrity 39 (2022) 441–449 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Table 5 Results of fatigue testing for Case 2

Specimen σ Ta , MPa

σ Cu , MPa

σ Steel , MPa

N

exp , cycle

Crack Initiation

F01

461

310

468

40 286

Ta

F02

451

304

458

39 023

Ta

F04

432

291

439

51 552

Ta

F05

413

278

419

63 816

Ta

F06

403

272

410

229 601

Ta

F08

384

259

390

358 111

Ta

F09

374

252

380

163 125

Ta

F10

365

246

371

422 936

Steel/Cu

F11

346

233

351

585 935

Ta

F13

336

226

341

350 382

Ta

F14

336

226

341

355 550

Ta

F15

461

310

468

81 979

Steel/Cu

5. Discussion 5.1 Crack origin

In Case 1 composite all the primary cracks formed in the tantalum layer and developed through the specimens leading to failure. Similarly, in Case 2 most of the primary cracks were spotted in the tantalum layer except for two specimens in which cracks formed at the interface between steel and copper. In Fig. 4 and 5 exemplary fracture surfaces of specimens with primary crack originating from the tantalum layer (Case 1) and at the interface (Case 2) were shown. The crack initiation region was circled and the directions of the crack growth were marked with arrows.

Fig. 4 Specimen C1F12 fracture showing initiation region and fatigue propagation direction