PSI - Issue 39

Branko Nečemer et al. / Procedia Structural Integrity 39 (2022) 34 – 40 Author name / Structural Integrity Procedia 00 (2019) 000–000

38

5

It is clear that the fatigue analysis of each loading level consists of three steps. In the first step, the number of cycles to failure for the first cell strut was numerically calculated. In the second step, the first cell strut was cut and two neighbouring cells were connected with a seam. Thereafter, the complete procedure was repeated for the second and third cells. Finally, the total fatigue life of the analysed structure was determined as a sum of all three periods.

First step

Second step

Third step

1 = 381 Cycles

3 = 1 Cycle

2 = 256 Cycles

Fig. 6. Schematic procedure for determining the total fatigue life of the analysed auxetic specimen

The computationally determined fatigue lives are summarised in Table 1. The computational results show that the number of cycles to failure decreases from cell to cell for the analysed auxetic specimen. From the computational results it is also evident that the fracture of cell struts appears in the corner of the individual unit cell and expanding in the direction of the maximum stress concentration.

Table 1. The computational results

Re-entrant auxetic specimen Number of cycles to failure [Cycle]

Rotated re-entrant auxetic specimen Number of cycles to failure [Cycle]

Amplitude force [N]

First cell

Second cell

Third cell

First cell

Second cell

Third cell

Total

Total

630 540 450 360 270

381 576 642 977 990

256 308 377 545 816

1 1

638 885

344 450 535 888

269 266 339 545

1 1

614 717

255 312 502

1274 1834 2308

207 252 747

1081 1685 4833

2171

1915