PSI - Issue 53

João Soeiro et al. / Procedia Structural Integrity 53 (2024) 367–375 Soeiro et al. / Structural Integrity Procedia 00 (2023) 000–000

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Fig. 6. SEM micrograph of the polymer-metal interface cross section (a), type of adhesion failure characterized by complete lack of adhesion at the interface (b), type of adhesion failure characterized by polymer fracture at the interface (c).

of the insert. On the other hand, concerning the parts where the metal surface was sanded (figures 7c and 7d), the type 2 adhesion failures are randomly spread out across the horizontal and vertical planes. This may indicate that the flame treatment was more e ff ective at not only eliminating type 1, but also type 2 adhesion failure.

Fig. 7. SEM micrograph of the polymer-metal interface cross section of flamed surface treatment showing good contact adhesion (a) and evidence of adhesion failure (b); SEM micrograph of the polymer-metal interface cross section of abrasion surface treatment showing good contact adhesion (c) and evidence of adhesion failure (d).

The SEM micrographs of the parts produced with inserts pre-heated at 50 ◦ C (refer to figure 8a and 8b) revealed a mixed outcome. Figure 8b displayed both type 1 and type 2 adhesion failures occurring simultaneously, indicating that the pre-heating at this temperature did not significantly impact the adhesion quality. However, 8a exhibited the formation of a polymer burr in the previously void gap suggesting a potential tendency for the polymer to maintain fluidity after being exposed to the metal or to remelt upon the application of the packing process. This could hint at an initial stage of improved adhesion, though further investigation would be necessary to confirm such hypothesis. The micrographs of figures 8c and 8d belong to parts injected with inserts pre-heated at 85 ºC. The more promising results show improved adhesion, relatively to the baseline part. While figure 8c displays better contact between the polymer and metal, full consistency throughout the interface is not achieved. Small type 1 voids are found in the irregularities of the metal surface, which are expected to hinder the flowability of the polymer melt. Additionally, type 2 adhesion failure is still observable in figure 8d Interestingly, the void between the first layer of the polymer and the rest of the material was almost non-existent, in comparison to other type 2 adhesion failure occurrences, pointing again to the tendency to fill the empty gaps. Similar observations can be made at 120 ºC. Figure 8e displays a consistent close contact throughout the polymer metal interface. However, 8f reveals the occurrence of localized, small-scale type 2 adhesion failures, which are visible as minor white cracks. It’s worth noting that these failures occurred in a connector track with a non-linear and irregular vertical plane, similar to 8c. Again, this condition should make it more challenging for the polymer to flow into the irregularities. However, this was not observed. Instead, the occurrences of adhesion failure were minimized, and in the form of type 2 adhesion failures, further endorsing the e ff ectiveness of the pre-heating insert strategy for enhancing adhesion.