PSI - Issue 28

Yifan Li et al. / Procedia Structural Integrity 28 (2020) 1148–1159 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The material data was obtained from the uniaxial tests in Section 3.2. The boundary conditions used in the FEA simulation was the same as in the fatigue tests. The upper and lower joints of the lattice ends were coupling with two reference points, respectively. The lower reference point was restrained in the all directions. The upper reference point was restrained in the x-direction and can only move along y-direction. Cyclic loading was applied on the upper reference point, and the loading of struts near crack tip was extracted to obtain the equivalent reversed load.

100 110 120

2 cells initial crack 1 2 cells initial crack 2 4 cells initial crack 1 4 cells initial crack 2 6 cells initial crack 1 6 cells initial crack 2

stage 3

0 10 20 30 40 50 60 70 80 90

stage 2

stage 1

Crack length (mm)

100

1k

10k

100k

1M

Number of cycles (N)

Fig. 9. The relationship between macro-crack length and number of loading cycles for lattice plate specimens of aluminium alloy 1050A pre cracked to different lengths (2, 4 or 6 cell widths).

Struts with the largest cross-section force were deleted to extend the fatigue macrocrack. Substituting equivalent reversible load into the Eq. (6), a prediction of the number of fatigue cycles to lattice failure can be obtained. At the same time, the force in struts along the crack path but not adjacent to crack tip were used to calculate damage accumulation. The simulated crack paths in all lattice plates are the same as in the fatigue experiment. In the 0° lattice plates, the fatigue crack propagates along direction 30° to the horizontal axis of preset edge crack in the upper half of lattice plate. The comparison of crack paths for a lattice with an initial crack 2 cells wide is shown in Fig. 10.

Fig. 10. Comparison of observed and simulated fatigue crack paths in a wide 2D triangular lattice plate containing an initial pre-crack 2 cells wide.