No abstract

No 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.

HE hot pressing of ceramic powders can be described using the plastic flow model proposed by Mackenzie and Shuttleworth for sintering.' In this derivation the porosity of the compact was assumed to be in the form of small, isolated, spherical pores which closed by means of surface tension forces. Assuming that the material behaved as a simple Bingham solid, the energy dissipated during viscous flow was equated to the work done in closing the pore. The resulting differential equation gave the rate of densification during sintering in terms of a viscosity and a yield point.In the present derivation it is assumed that the principal driving force for the closure of the pores is the applied hydrostatic pressure rather than the surface tension of the pore. The pressure effective in closing the pores depends on the density of the compact, and rather simple considerations suggest a correction termwhere PA is the applied pressure and D is the relative density. When this pressure term is substituted for the surface tension term in the Mackenzie-Shuttleworth expression, the differential equation for densification during hot pressing is found to be T K = x = D = 9 = t = P = 7 = CD = K X (-) 1 + a l n x dt

No abstract