PSI - Issue 28

Rhys Jones et al. / Procedia Structural Integrity 28 (2020) 364–369 Rhys Jones/ Structural Integrity Procedia 00 (2019) 000–000

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5

used to predict crack growth was:

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(5)

In this analysis, as a result of the high value of the applied stress (910 MPa) the Irwin correction factor was used to correct the stress intensity factor solutions for the effect of crack tip plasticity. The resultant computed curve for crack length versus cycles is also shown in Figure 3, where good agreement between the measured and computed crack length histories is observed.

10

Measured Computed

1

a (mm)

0.1

2000

2500

3000

3500

4000

Cycles

Fig. 3. . Comparison between the measured and predicted crack growth histories for the AM Ti-6Al-4V specimen with a yield stress of approximately 1120 MPa.

4. Conclusions The certification requirements for additively manufactured (AM) replacement parts require an ability to accurately predict the growth of small sub mm cracks. To this end, it is shown that the Hartman-Schijve crack growth equation proposed in a prior paper for (small) crack growth in LENS Ti-6Al-4V reasonably accurately predicts the growth of small cracks in the two LB-PBF Ti-6Al-4V specimen tests. The initial crack size in this study is comparable to the minimum equivalent initial damage size (EIDS) in the USAF approach to the certification of an AM replacement part.

References

1. Jones, R., Raman, RS., Illiopoulos, AP., Michopoulos, JG., Phan, N., and Peng, D., 2019. Additively manufactured Ti-6Al-4V replacement parts for military aircraft, International Journal of Fatigue, vol. 124, pp. 227-235. 2. McMichael, E., Frazer, E. NAVAIR Additive Manufacturing, 2015. Proceedings Summary Report: Joint Federal Aviation Administration Air Force Workshop on Qualification/Certification of Additively Manufactured Parts, DOT/FAA/TC-16/15, 2015 (Available online: