Role of the inter-ply microstructure in the consolidation quality of high-performance thermoplastic composites

Abstract

Consolidation of Carbon Fiber (CF)/high-performance thermoplastic composites is much less understood than the one of their thermoset counterparts. It is usually assumed that the consolidation quality is directly linked to the removal of voids within the sample during consolidation, leading to mechanical properties suitable for aerospace applications. A systematic study of the temporal evolution of CF/polyetherketoneketone (PEKK) samples' microstructure consolidated under low pressure in a rheometer is related to the increase in inter-laminar shear strength. The results show that despite similar void contents well-below 1 vol%, samples can present significant differences in ILSS values, from 80 to 95 MPa for cross-ply samples, and from 98 to 112 MPa for unidirectional (UD) ones. A microstructural analysis shows that, for these materials, consolidation quality is rather related to a reorganization of the inter-ply, a resin-rich (~70 vol%) region of typical thickness 10 μm which is slowly repopulated in fibers during consolidation. Highlights: Microstructure of CF/PEKK composites is characterized over consolidation time Contrary to thermosets void content cannot be used to predict mechanical properties ILSS increase over consolidation time is related to inter-ply reorganization Inter-ply microstructure and ILSS have a direct correlation The repopulation in fibers of the resin-rich inter-ply is a slow process.