Non-isothermal stamp forming of continuous tape reinforced all-polypropylene composite sheet

This paper describes the thermoforming behaviour of a self-reinforced composite based on co-extruded polypropylene (PP) tapes. In contrast to traditional continuous woven glass fabric reinforced polypropylene (GF/PP) materials, where the sole mode of deformation is either inter- or intraply shearing, all-PP composites have an additional mode of deformation as here the fibres (or in this case tapes) can still be deformed. The importance of this additional deformation mode is investigated in a range of stamping experiments in combination with 3D strain mapping experiments. Non-isothermal thermoforming experiments revealed that all-PP woven fabric laminates based on flat tapes deform in a different manner to traditional GF/PP. Although the main mode of deformation of both all-PP and GF/PP for the investigated dome parts was intraply shearing, a much lower energy was required to deform the all-PP laminate. Whenever possible, deformation of the tape by drawing should be avoided as it requires higher energy which may lead to higher residual stresses in the final part. However, tape drawing may prove an essential benefit when complex shapes are involved.