A study of the deformation of weft-knit preforms for advanced composite structures Part 1: Dry preform properties

Abstract

A weft-knit preform has the potential for its mechanical properties to be tailored, by virtue of the 3-D path of the yarns, in a variety of knitted constructions. The exceptional formability properties (i.e. the ability of a textile preform structure to conform to a 3-D shape) that weft-knit preforms have enable the fabrication of 3-D composite structures by means of resin transfer moulding (RTM). This paper is part one of a two-part series, in which the deformation of weft-knit preforms by the use of a modified California bearing-ratio (CBR) test method is examined. This paper reports the relationship between the physical, mechanical and simulated formability properties of weft-knit glass-fibre preforms. The results for the full milano structure showed that the plain loop length and tensile properties enabled a good prediction of simulated formability. It also investigates the effects of different knit structures on the deformation of weft-knit preforms. The other structures examined include the alternating half milano, full milano, French double piqué and full cardigan. The results in this section indicate that irrespective of structure, the loop length and tensile properties determine the simulated formability of weft-knit preforms. The second paper provides a composite case study for the formability of weft-knit reinforced composites.