PSI - Issue 42

Stefan Sieberer et al. / Procedia Structural Integrity 42 (2022) 72–79 S. Sieber r et al. / Structur l Integrity Procedia 00 (2019) 000–00

76

5

 1 x10^-2

0.8

shaft

0.7

0.6

0.5

0.4

neck

0.3

eye

0.2

0.1

0

Fig. 4. DIC plots of the specimens before failure. From left to right: Specimen 1, Specimen 2, Specimen 3. DIC strain evaluation areas are indicated in the shaft, neck, and eye region.

3. Results and Discussion

3.1. Strength and sti ff ness

Figure 4 shows DIC obtained principal strain distributions before fracture in the specimens. The evaluation areas for the strain in the shaft, and for the strain concentration factors to the neck and eye are indicated. The part strength and the sti ff ness of the shaft are given in Table 2. Additionally, the strain concentrations K neck and K eye , and the bearing sti ff ness are tabulated. The strain concentration factors are similar for all three tested specimens, although the position of the strain measurement in the eye and neck region is not fixed for reasons of DIC correlation discrepancies. Because of slight variations in the speckle pattern or light change between tests, not all boundary regions could be analysed to acceptable quality by the software for all specimens. However, assuming symmetry, neck and eye regions were evaluated for all three specimens. A di ff erent DIC speckle pattern was applied to Specimen 1, however, larger areas of correlation are obtained with the pattern used on Specimens 2 and 3. Generally, because DIC uses finite regions to determine strains, the edge of a specimen will not be analysed. This is not a problem for the current part investigation, because the load bearing CCF are printed within a TP boundary layer, which does not carry significant load. A marked di ff erence in performance is visible when printing more layers of the material and thus obtaining a higher fibre volume fraction. The increase in strength by fibre volume fraction increase of 10 % is 11513 / 7215 = 1.60, sti ff ness increase ins shaft is 43.1 / 31.6 = 1.36. The strength increase is significantly higher than predicted by the rules of mixture from classical laminate theory and the recent investigation by Hou et al. (Hou et al. (2020)), and may be because of additionally reduced void content in the specimens (Polyzos et al. (2021)). The sti ff ness increase in the shaft reflects the 37% increase in φ very well. In Figure 5, the strains at shaft, neck and eye are shown for Specimens 1 and 2.

Table 2. Test result overview. Specimen

Strength in N

Sti ff ness in GPa

Strain concentrations eye / neck

Bearing sti ff ness in kN / mm

Specimen 1 Specimen 2 Specimen 3

11513

43.1 33.9 29.3

3.0 / 2.8 3.0 / 3.0 2.5 / 2.8

9.9 8.6 8.0

6916 7415

The strain concentrations (Figure 6) is shown over load application and only in the specimens with lower φ , nonlinear