Characterising the creation of defects in large scale vacuum assisted resin infusions in the marine industry

Abstract

Utilisation of the Vacuum Assisted Resin Infusion (VARI) process has increased in recent years for the manufacture of large scale components for the transport industry. Quality control and repeatability are two key areas where the VARI process requires greater understanding due to the scale of the infusions. The marine industry has a history of being at the cutting edge of large scale composite manufacturing. This research focusses on utilising the processes and knowledge at Princess Yachts International (PYI) to monitor and analyse the process variability and uncertainty for large scale VARIs.
A detailed process review was conducted at PYI to evaluate the level of process monitoring and variability as well as the defect controls that are used in industry. Core samples were extracted from infusions where surface visible defects had been recorded. The core samples were analysed using Micro Computed Tomography (µ-CT) to generate a three-dimensional reconstruction of the defects. The location and structure of the defects indicated matrix failure towards the mould surface of the component, an area which is not monitored during the VARI process.
Having identified a requirement to monitor the manufacturing process, a review of available sensors was conducted identifying Fibre Bragg Grating (FBG) fibre optics as the most suitable monitoring method. The sensors measured the residual stress development during resin curing as well as the high loads exerted on the component during demoulding which were five times larger than during the infusion and resin curing process. The measured strains were lower than the failure strain of the resin suggesting the presence of defects that result in premature matrix failure.
A novel approach to monitoring resin flow was then developed to analyse the through thickness resin flow progress using µ-CT. Both monolithic and sandwich laminates were analysed both in-situ and exsitu to evaluate the effect of variable laminate layup. The results further identified the high degree of variability during the infusion caused by changes in laminate schedule and the transition from sandwich to monolithic sections.

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ORCID for James Blake: orcid.org/0000-0001-5291-8233

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