PSI - Issue 56

Dan Micota et al. / Procedia Structural Integrity 56 (2024) 144–152 Dan Micota / Structural Integrity Procedia 00 (2019) 000 – 000

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thickness (3.2 mm) results are presented side by side with the lower wall thickness (2 mm) test results from Micota, Isaincu, & Marsavina, (2021), keeping also the same curves scale for a good comparison and visualization of the wall thickness influence at each orientation for both materials. As 5 specimens were tested for each material, wall thickness and orientation, only one representative curve was plotted for good graphs intelligibility.

(a)

(b)

Fig. 2. Engineering stress-strain curves for PPA-GF33 with low 2 mm wall thickness (a) and increased (3.2 mm) wall thickness.

At a quick glance over the curves for PPA-GF30 it is obvious that the increase in wall thickness has a major influence over the mechanical properties of the injection molding plates specimens. One of the overall tendencies is that the strength (stress) is decreasing with the increase in wall thickness for the lower angles-oriented specimens (0°, 15°). While the strains at break are substantially decreasing with the increase in wall thickness for the higher angles-oriented specimens (30°, 45°, 60° and 90°). Average values of the stress and strains at break can be read in Table 1, together with the standard deviations and the percentual coefficient of variation, calculated for each of the 5-specimen batch. The values for Young’s modulus are also in Table 1, as they are less observable from the graphs. Table 1 also contains the percentual difference compared to the values of the 2 wall thicknesses, with the proper signs for decrease (-) or increase (+) of the 3.2mm specimens values over the 2mm specimens.

(a)

(b)

Fig. 3. Engineering stress-strain curves for PPS-GF40 with low 2 mm wall thickness (a) and increased (3.2 mm) wall thickness.

Looking over the side-by-side graphs for the 2mm and 3.2mm thick PPS-GF40 specimens from Fig.3 it can be observed that the brittleness on the thicker specimens is increased as less plasticity is present, and strain at break over the whole orientation range is significantly decreased. For this material the stress at break is also strongly reduced for the higher thickness specimens for all angles/orientations except 90°.