PSI - Issue 34

Alexander Berndt et al. / Procedia Structural Integrity 34 (2021) 105–110 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2.2. Specimen manufacturing Conventional FDM printing is limited by three axes. By using a fourth cylindrical rotating axis, fiber angles can be manufactured as in the winding process. Figure 2a) shows a schematic design of a modular build fourth axis which can be implemented in any open-source 3D printer. Figure 2b) shows the actual implemented fourth axis in an opened Markforged MarkTwo printer. By adjusting the rotational speed of the cylindrical axis, it is possible to change the fiber angles of each printed layer. The printing temperature was T p = 275 °C, and the printing speed v p = 30 mm/s.

Figure 2. a) Schematic design of a modular implementable fourth axis. b) actual implemented fourth axis in an opened Markforged MarkTwo Printer

A total of 25 samples were printed. Starting from α = 15° fiber angle [+15, -15,0,0] S up to α = 75° fiber angle with a 15° angle increase, which results in five specimen per set. The dimensions of each CCF crash tube are given with d i = 40 mm, d a = 42 mm and an initial length l i = 100 mm . Crash tubes were sharpened with an own 3D printed sharpener with integrated carbide blades to provide a 45° chamfer for damage triggering. 2.3. Experimental setup and investigations Before crushing the CCF crush tubes, their initial weight m 0 was measured. Tubes were then compressed at 10 mm min-1 for a total of 80 mm crosshead displacement in the ZwickRoell Z020 universal testing machine (Figure 3a). Test videos were recorded with an iPhone 12 Pro. The energy absorption capability of CCF crash tubes was examined. Therefore, the values of force and displacement were recorded. A force-displacement diagram was created from the data.

Figure 3. a) Experimental setup of the crush testing on the ZwickRoell Z020. b) Progressively crushed cylindrical composite Solaimurugan et al. (2007)

Figure 3b) shows the formed petals due to axial crack and circumferential delamination. During the crushing process the petals are bend away and bent plies are broken Solaimurugan et al. (2 007) . The efficiency of the crash tube during the quasi-static compression test is determined by the crush force efficiency. This is the ratio between the average crushing force and the maximum crushing force (1).