Experimental methodologies for CFRP characterisation and compression moulding process optimisation

This doctoral research was carried out in collaboration with C.P.C. S.r.l. (Modena, Italy) and aimed at the characterisation of composite materials. The work focused on thermosetting carbon-fibre-reinforced polymer (CFRP) for compression moulding, developing experimental methodologies to describe how material behaviour evolves along the processing chain, from neat resin state to moulded parts. A central part of the study addressed the rheological and calorimetric characterisation of three epoxy resin systems used as matrices for prepreg compression moulding (PCM). Viscosity measurements were performed to evaluate flowability and gelation points, while DSC analyses were used to investigate curing behaviour and reaction kinetics. This evaluation enabled the construction of time–temperature–degree of cure maps, which served as a basis for selecting curing temperatures and times for compression moulding trials. The resulting laminates were characterised by DMA to verify the consistency between DSC-based predictions and the network development achieved during processing. The second contribution addressed the quantitative characterisation of prepreg tack for PCM applications through the development and application of a probe-tack methodology adapted to carbon-fibre epoxy prepregs. Specific testing parameters were defined to objectify a property typically assessed qualitatively in industrial practice. Two measurable indicators were introduced: the maximum tack stress (σmax) and the work of adhesion (Wadh). The results showed how freezer ageing and out-life exposure modify the viscoelastic response of the matrix. The third part addressed the fibre-to-matrix ratio in CF-SMC plates. Two complementary thermo-analytical methodologies were developed and validated on specimens extracted from SMC moulded plates: a controlled muffle-furnace cycle for bulk samples and a TGA-based protocol for small-scale analyses, both based on the selective oxidative thermal degradation of the thermoset matrix. The TGA method was also verified on uncured PCM prepreg. The combined approach provided a reproducible framework for accurate determination of local fibre/matrix content in CF-SMC moulded plates.