Temperature field evolution and thermal-mechanical interaction induced damage in drilling of thermoplastic CF/PEKK – A comparative study with thermoset CF/epoxy

Abstract

Although new generation carbon fibre reinforced thermoplastic (CFRTP) such as carbon fibre reinforced polyetherketoneketone (CF/PEKK) is a promising sustainable alternative to the conventional thermoset CFRP, there is a lack of literature regarding its machining performance. This is the first study unveiling the hole wall and chip temperature evolution during drilling of thermoplastic CF/PEKK composite and the resulting material damages have been studied in detail. Through comparative study with CF/epoxy, the disparate drilling performance of the two composites has been uncovered, and the results were found to be closely related to the materials’ thermal/mechanical properties. Specifically, CF/PEKK produces continuous chips due to its excellent ductility and thermal sensitivity, whereas CF/epoxy produces segmented chips due to its brittle nature. CF/PEKK generates up to 40 N (50.5%) higher thrust force, 87.6 ℃ (98.9%) higher hole wall temperature and 61.1 ℃ (48.8 %) higher chip temperature than that of CF/epoxy. This has been correlated to the longer tool-chip contact length of CF/PEKK and its unique chip morphology. Despite the greater thrust force/temperature generation, CF/PEKK shows 55.7% lower delamination damage than CF/epoxy, and this is owning to its excellent interlaminar toughness. This study establishes a more in-depth understanding into the drilling performance of thermoplastic CF/PEKK and thermoset CF/epoxy and also provides guidance on the high performance manufacturing of next generation CFRPs.

Multi-objective optimization of thermoplastic CF/PEKK drilling through a hybrid method integrating NSGA-II and TOPSIS: an approach towards sustainable manufacturing

“…The chips' compliance to the cutting edge resulted in enlarged tool-chip contact length and generate more frictional heat [33]. Our findings exemplify the strong influence of composite's thermal / mechanical properties on the resulting chip morphology, which consequently affect the drilling induced temperature.…”

“…In comparison with CF/epoxy, the Tmax of CF/PEKK is up to ~100 ℃ higher. The drilling induced CF/epoxy chips are mostly in powdery form according to previous studies by Ge et al [33] and Xu et al [41]. Due to thermoset epoxy's better thermal stability, the softening of CFRP under machining induced high temperature is rather limited.…”

“…The thrust force was measured using a dynamometer (Kistler 9272) coupled with charge amplifier (5070A) and data acquisition unit (5697). The maximum hole wall temperature was captured using a 125 Hz FLIR A6751 thermal camera with the holes drilled 0.5 mm from the composite edge following previous study [33], see Fig. 1 (a).…”

“…It is worth mentioning that the thrust force of CF/PEKK can be up to ~ 50 N higher than CF/epoxy. This could be the result of the presence of softened and continuous CF/PEKK chips, which are hard to evacuate, hence induced additional resistance at the tool/workpiece interface during drilling [33].…”

“…This difference can be attributed to the different delamination damage mechanisms of CF/PEKK and CF/epoxy. Delamination damage of CF/PEKK shows typical thermal-mechanical interaction characteristics [33] and the fact that its high drilling temperature approaching / exceeding the Tg can soften the thermoplastic PEKK matrix and weaken its resistance against deformation. Therefore, under low feed rate (Ff ≤ 0.05 mm/rev), even the thrust force is quite low, the high drilling temperature (see Fig.…”