PSI - Issue 61

Albert E. Patterson et al. / Procedia Structural Integrity 61 (2024) 148–155 Author name / Structural Integrity Procedia 00 (2024) 000–000

150

3

(a)

(b)

(g)

Shell region around crack tip

(f)

1 mm

1 mm

Printed notch (no treatment)

Printed notch (pre-cracked)

Shell separation

(c)

(d)

Ideal crack path

1 mm

1 mm

(e)

Machined notch (no treatment) Machined notch (pre-cracked)

Fig. 1. Example notches, (a) printed with no treatment, (b) printed and pre-cracked, (c) machined with no treatment, (d) machined and pre-cracked, and (e) notch machining process with (f) example ABS specimen before notching. (g) Extra cracks and shell separation observed in the printed notches which did not have pre-cracks.

Table 1. Factor combinations and results from the notching method analysis. Fracture load was the maximum load before fracture of the CT specimens.

Fracture Load (N) Mean Stdev

Combination Material

Notch Style

1 2 3 4 5 6 7 8 9

ABS Printed, no treatment PC Printed, no treatment PLA Printed, no treatment

300.1 502.8 561.7 326.2 579.1 578.5 380.6 658.9 692.3 348.9 648.5 683.3

15.2 23.7 68.4 55.5 34.0 31.1 51.0 19.7 21.7 48.6 42.8 6.8

ABS Printed + razor blade treatment PC Printed + razor blade treatment PLA Printed + razor blade treatment

ABS Machined, raw PC Machined, raw PLA Machined, raw

ABS Machined + razor blade treatment PC Machined + razor blade treatment PLA Machined + razor blade treatment

10 11 12

likely explain the e ff ect observed. When the notches are machined, the shell is removed completely and the infill area is able to absorb slightly more energy before failing since it is more flexible without the shell. Based on these observations, it was concluded that the results of three of the cases (printed notch + pre-crack and the two machined notch cases) were valid and the di ff erences in performance are easily explainable. For the fourth case, some crack tip e ff ects from the shell caused some strange results which need to be further explored. Until this e ff ect is better understood, raw printed notches should not be used for fracture testing FFF-processed materials. From a design perspective, it does not matter much which of the three valid methods are used (as long as the selected method is used consistently) since the point of design-driven fracture tests is to collected comparative information and design knowledge, not build constitutive material models. With these observations, the data provided and the recommendations of ASTM D5045, it was decided that future experiments related to these materials can use either machined or printed notches but that pre-cracking is essential in either case.

3. E ff ect of Element Layout

In the first part of the study using three common FFF-processed thermoplastics (ABS, PLA, PC), di ff erent notching methods were explored for ASTM D5045 CT samples; it was concluded that machined notches with pre-cracks