Folding of Continuous Fibre Thermoplastic Composites

Thermoplastic composites with continuous fibres are attractive construction materials because of their good specific mechanical properties and their possibility to be processed very rapidly. An extremely fast processing method is folding of sheet material. Folding can be performed by local heating of a sheet along a line. Heating is done to a temperature, well above the softening or melting point of the thermoplastic polymer. Subsequent folding along the heated line requires very low forces. The folded geometry becomes permanent after cooling below the softening point of the polymer. Unfortunately, folding causes microbuckling of the reinforcing fibres at the compression side of the fold causing a severe reduction in the local strength. The present report describes a method for the folding of thermoplastic composites, which controls the direction of fibre microbuckling. The method results in a smaller strength reduction. The folding equipment is designed in such a way that microbuckling of the fibres occurs in a direction in the local plane of the sheet rather than being perpendicular to that plane. The result is a folded sheet with a reduction of about half of the original strength, as compared to a strength of only 15% of the original strength, which is typical for folds produced with more conventional means. In other words, the remaining strength is more then doubled using the new folding technology.