The influence of variation in process parameters on the manufacturing of advanced fibre composites

Abstract

The high speci c and tailorable properties, and high corrosion resistance of composite materials, make them a desirable material choice in a wide range of industries. To date, composite materials have typically been manufactured in low production quantities, using primarily manual manufacturing methods. This lack of automation of the manufacturing process, gives the potential for variations in process parameters to have a signi cant e ect on the morphology and mechanical performance of the produced laminate. This research focuses on the in uence of ambient temperature variations on wet hand layup with vacuum consolidation and resin infusion, and the pre-cure air removal process for out-of-autoclave prepreg. Such variations in these processes are commonplace in the marine composites manufacturing industry, which is the focus of this work. Ambient temperature has a strong e ect on the processing properties of liquid epoxy resins, in particular the evolution of cure and viscosity. The in uence of temperature on these parameters for two epoxy resin systems was quanti ed using di erential scanning calorimetry and rheometry, and a cure and viscosity model was developed that enabled the prediction of cure and viscosity for any time-temperature history. In order to assess the in uence of these variations in processing parameters on actual laminate manufacture, panels were manufactured on an instrumented mould surface, under controlled environmental conditions. This showed that both processes were surprisingly robust to variations in processing parameters, due to the high resin bleed restriction imposed by typical consumable layouts. In order to quantify the critical process parameters of out-of-autoclave prepreg materials, and improve the understanding of their air removal behaviour, a novel characterisation method was developed and applied to two prepreg bre architectures; cloth and unidirectional. The prepreg bre and resin content, and open and closed cell porosity in the uncured state were quanti ed using a novel gas pycnometry technique. The compaction response and in-plane and through-thickness air permeability were measured independently, allowing the decoupling of the compaction and permeability behaviour of each material. Based on the permeability behaviour, it was found that air removal occurs primarily through-thickness for the cloth material and in-plane for the unidirectional material, for typical laminate geometries. The compaction and permeability models were implemented into a one-dimensional air removal model, which showed that for typical laminate geometries, the air removal from the cloth happened nearly instantaneously, whereas the air removal from the unidirectional was signi cantly slower, and would require accurate process speci cation to ensure all air was removed before the cure cycle began.