Community Research and Development Information Service - CORDIS

Development of knitted fabrics for industrialization of high performance composites

The aim of this Craft project was to develop the RTM process for composites based on knitted fabrics. To this end, the properties of knitted fabrics, in both processing and mechanical aspect, were investigated. Comparison was made with conventional woven and braided fabrics as well. Furthermore, parts were designed and manufactured in view of the real applications.

With fabric compression tests, the relationship between fibre volume fraction and compression pressure was established for different types of preforms. Except for the knitted fabrics, significant relaxation behaviour was observed. By a simple method, the compressibility of Multimat (a combination of knits and mats) is related with its components, mat and knit.

Permeability measurements revealed that knitted fabrics are much more permeable than the woven fabrics in the practical range of fibre volume fraction (defined as the fibre volume fraction achievable in the pressure range of the RTM equipment).

The tensile modulus of the knitted fabric composites is comparable with the woven fabric composites. The knitted fabric composites show the additional advantage of a high capability of energy absorption and a high damage tolerance during impact. However, the tensile strength of the knitted fabric composites is much lower, limiting its use in engineering applications.

The problem of low strength was solved with the introduction of Multimat. Its composites show considerably higher strength than the knitted fabric composites. The flexural properties are even better because of its sandwich structure. Furthermore, the drapability and permeability are improved compared with the mats thanks to the knitted fabric. Good impact properties are retained at the same time.

Body panels and stiffeners for a truck were produced with Multimat. The processing time was reduced dramatically due to the high drapability of the fabric. The stiffeners were tested in 3-point bending test and the results were compared with FEM calculation.

Interrupted RTM flow was performed by using a hemispherical mould. The observation of the flow front progress was compared with simulation results. Good agreement was obtained.

Reported by

Katholieke Universiteit Leuven
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