PSI - Issue 37

Yifan Li et al. / Procedia Structural Integrity 37 (2022) 41–48 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

47 7

The fatigue crack growth rate and SIF range were calculated according to the secant method suggested in the ASTM E647-15 (2015). In secant method, crack growth rate simply involves calculating the slope of the straight line connecting two adjacent data points on the a versus N curve. = +1 − +1 − (6) ∆ = 1 2 (∆ + ∆ +1 ) (7) where j+1 and j represent two neighboring data points of experimental results. The fatigue crack growth rates of different orientation lattices are shown in Fig. 8. The material parameters in terms of Paris’ law, C and m, are determined from this result. Fig. 8 illustrates that the fitted curves of crack growth rates of different orientations lattices were nearly horizontal. The crack in orientation-Y lattice grows fastest under the same ∆K, and octet -truss lattice in Z orientation has excellent resistance to fatigue crack propagation.

da/dN=1.56E-7 *(  K ) 5.84

1E-02

da/dN=1.57E-9 *(  K ) 7.71

da/dN=1.20E-8 *(  K ) 5.91

1E-03

da/dN (mm/cycle)

Orien-X Orien-Y Orien-Z

1E-04

6

7

8

 K (MPa • mm 0.5 )

Fig. 8. The crack growth rates of lattices in different orientations.

4. Conclusion The orientation effects on the fatigue properties including crack propagation rates of octet-truss lattices are studied in the present research. All orientations samples are printed by photopolymer into compact tension geometry. The experimental results show that orientation has significant effects on the fatigue crack paths. The crack paths of orientations X and Z specimens are almost horizontal to the initial crack, but the crack of orientation-Y specimens is rotated by 30◦ to the initial crack plane. The crack in orientation- Y lattice propagates fastest under the same ∆K and orientation-Z lattice has excellent resistance to fatigue crack propagation. The fitted curves of crack growth rates of different orientations lattices in the log-log plot were nearly horizontal. References ASTM E647-15, 2015. Standard Test Method for Measurement of Fatigue Crack Growth Rates. ASTM International. West Conshohocken, PA. Burr, A., Persenot, T., Doutre, P. T., Buffiere, J. Y., Lhuissier, P., Martin, G., Dendievel, R., 2020. A numerical framework to predict the fatigue life of lattice structures built by additive manufacturing. International Journal of Fatigue 139, 105769. Chen, X. Y., Tan, H. F., 2018. An effective length model for octet lattice. International Journal of Mechanical Sciences 140, 279-287.