Analytical modelling for sheet thermoforming of knitted fabric reinforced PMC

Abstract

Knitted fabrics are known for their excellent stretching and draping properties due to their curved fabric architecture. In recent years knitted fabrics have been used as reinforcement network for polymer sheet thermo-processing. This paper describes a method for evaluating the product height, product profile and strain distribution of a flat polymer matrix sheet, reinforced with knitted fabric, undergoing the sheet thermoforming process. The availability of a knitted fabric reinforced PMC to stretch is proposed to be equal to the least ratio of curved loop length to its projected length. The product profile is then obtained from the availability of the material to stretch and the tool geometry involved. Finally a mapping scheme is proposed to evaluate the severity of deformation in terms of strain distribution. A reasonably good agreement is observed between the model and experimental results. An understanding of the severity of deformation distribution would shed light on the location of highest degree of deformation as well as its magnitude and should therefore assist the product designer in dealing with the thermoforming process of this new material.