Permeability Characterisation of
Continuous Filament Mats for Resin Transfer Moulding

EPSRC Industrial CASE studentship
in partnership with Plastech TT Limited (2004-2007)

This research sought to examine both permeability measurement and material characterisation of Continuous Filament Mat (CFM) glass fibre reinforcements. As an alternative to fabrics, which generally provide higher in-plane properties, CFMs are often employed as low cost, "lofty" (high uncompressed thickness, and therefore good specific flexural stiffness), easy to process reinforcements for Resin Transfer Moulded (RTM) parts.

Within this project, investigation of permeability measurement has involved the development of two (radial and linear) liquid flow permeability techniques to provide a reliable and robust data set for a specific CFM (Unifilo U813-300). Then two novel (radial and linear) airflow techniques were developed for the measurement of CFMs, these providing comparative results with the liquid flow measurements. The benefits of airflow versus liquid flow include cleaner, lower pressured flow using a fluid that may be produced by compressor rather than stored, therefore having significant benefits for both laboratory and industrial measurements of permeability.

Material characterisation is necessary to analytically investigate reinforcement materials, as permeability has a non-linear relationship with overall porosity. Permeability is therefore considered as a function of pore distribution, which encompasses the two scales of intra and inter fibre-bundle flow. Two areas have been investigated, these involving permeability measurement and microstructure characterisation. Comparative permeability measurements of a second CFM (Unifilo U850-300), consisting of a different arrangement of fibre bundle sizes, were undertaken using the 1D airflow method, and inter-laminar flow was investigated using the radial airflow method. These resulted in a permeability ratio of between 0.54 and 0.64 (U813/U850) across a 0.1 to 0.3 fibre volume fraction range for the two CFMs, and no significant inter-laminar pore space effect.

Microstructural characterisation initiated with image analysis of electron micrographs, providing measurement of fibre diameters and intra-bundle porosity. Kozeny-Carman modelling then showed the permeability of intra-bundle areas to be insignificant resulting in a focus on inter-bundle flow. Although limited by assumptions made for various material parameters, semi-empirical models to provide inter-bundle porosity and fibre bundle geometries were developed. Relation with permeability was then achieved through calculating hydraulic radius and mean hydraulic radius and provision of a range of Kozeny constants (0.55 to 6.17) and coefficients to replace the Kozeny constant, which provide upper and lower bounds for the remaining factors of permeability.

The overall future industrial benefits for material engineers rely on the addressing of these limitations for quantifying geometries, so as to provide clarity of the relationship between controllable material parameters and permeability. Towards this goal, suggestions of further work here investigate employing micro-CT imaging and the use of 3D modelling that have the potential to use real-world images rather than idealised geometrical models.

Researcher = Ross Pomeroy

After 10 years of working for HM Customs and Excise, Ross entered HE at the University of Plymouth. Ross first completed a year-zero in ‘Extended Science’ and then progressed to achieve (2004) 1st class honours from the infamous BSc (hons) Surf Science and Technology degree. Directly from this BSc, he progressed to a PhD in the field of composite materials engineering.

During his full time PhD studies Ross undertook an increasing lecturing load, and successfully obtained a full time lecturing post, for the marine sports programmes at the University of Plymouth, at the end of his third year (2007). Two years later (2009) Ross was promoted, on a 5 year secondment, to the academic senior management position of ‘Subject Forum Chair for Science and Technology’ for the University of Plymouth Colleges faculty (UPC). This role involves both quality assurance and academic development from the position as chair of a forum of programmes delivered in partnership between the University and (currently) thirteen of the University’s partners, the majority of which are colleges of further education, although these also include commercial and governmental training providers.

The current post is not research focused.  However, Ross remains active where possible. He is currently: awaiting feedback on a submitted pedagogic paper on the use of GoogleDocs for level-4 assessments involving the collaborative writing of tensile testing laboratory reports; in the process of writing up further papers from his PhD thesis; currently heading a research team for a University of Plymouth Teaching Fellowship Award, involving the use of XING/FLUX as an induction tool; and is 3rd supervisor for a PhD student who started at the University in January 2011".

Publications arising from this research:

  • R Pomeroy, S Grove, J Summerscales, Y Wang and A Harper, Measurement of permeability of continuous filament mat glass fibre reinforcements by saturated radial airflow, Composites Part A: Applied Science and Manufacturing, 2007, A38(.), 1439–1443.
  • R Pomeroy, S Grove, J Summerscales, Y Wang and A Harper, Measurement of permeability of continuous filament mat glass fibre reinforcements by saturated radial airflow, 8th International Conference on Flow Processes in Composite Materials (FPCM8), Douai - France, 11-13 July 2006.
  • R Pomeroy, Preform Characterisation for Resin Transfer Moulding, BAMPE/BCS Annual Student Seminar, London, 22 November 2005.

Electron micrograph

Binarised electron micrograph

Electron microscopy image of U813-300:
original image (above) and manipulated image
where tows have been solidified (below)