PSI - Issue 34

Sanne van den Boom et al. / Procedia Structural Integrity 34 (2021) 87–92 Sanne van den Boom et al. / Structural Integrity Procedia 00 (2021) 000–000

90

4

(a)

(b)

Fig. 3: Optimized designs. Figure (a) shows a cut view of the sliced design B - optimized infill , where the denser infill regions are clearly visible. Figure (b) illustrates design C - optimized design .

Nozzle temperature 230 ◦ Bed temperature 80 ◦ Chamber temperature 20 ◦ Nozzle size

0 . 6 mm 0 . 3 mm

Layer height

Extrusion multiplier

1

(a)

(b)

Fig. 4: Print settings used for the preparation of the specimens (a). The chamber was not heated, but the chamber temperature was allowed to fluctuate due to the printing process and external temperature. Test setup (b): the ladder step is placed on a mounting piece which has conical rubber stops and a slanted surface. On the the top the 90 mm wide rubber loading part is visible. The ladder step has a black speckle pattern for the DIC measurements.

regions are used. For the uniform infill specimens and the optimized infill specimens, wall layers consist of 3 roads, resulting in 1.5 mm walls. The specimens for design C - optimized design are printed as solids, which is achieved by setting the number of top and bottom layers to 999. Standard settings are used for brim and support structures. All specimens are coated with a speckle pattern of black paint for DIC measurements and weighed, see Figure 7b. The design B - optimized infill specimens are lighter than the design A - uniform infill specimens, however the design C - optimized design specimens are considerably heavier. While this can be partially explained by the fact that the design C - optimized design has internal support structures that are di ffi cult to remove, it is mostly caused by extracting an iso surface for the optimized design at a certain density level, and then considering that STL as a solid. Nevertheless, even di ff erent versions from the same design have di ff erent weights. This may be caused by impartially removed support structures or by small disturbances in the printing process. Experimental setup The specimens are secured on a support structure where the holes are supported using conical rubber stops and the back of the specimen is supported by a slanted surface. A 25 ton bench is used to apply a quasi static displacement of 4 mm / s, with a rectangular rubber slab of 90 mm wide spanning the entire depth of the ladder step. As the bench will also measure the sti ff ness of the rubber stops and the rubber loading slab, DIC measurements are employed to extract the deformations and strains of the part. Figure 4b shows a photo of the test setup including a specimen with the speckle pattern for DIC measurements. In order to match the DIC measurements to the force displacement curve extracted from the bench, the displacements of the bench itself are also traced with DIC. This way, the force from the bench can be connected to a time step in the DIC results, and the corresponding deformations and strains can be found from there.

5. Results

Figure 5 compares the DIC measurements to the numerical simulations for all three designs. The distributions of strains are very similar. Furthermore, it is shown that high strains are located in the corners near the middle support.