THE CREATION OF DUCTILE, COMPOSITE PREPREGS, WITH CLOSE TO UD PROPERTIES

摘要

The vast majority of structural composite parts are nearly two-dimensional and can be tape laid (ATL) at moderate speed. More complex parts can be laid using Automated Fibre Placement (AFP) but at much reduce speed and hence increased cost. One current solution is to use an ATL to make a flat laminate and then to form the part by drape or press forming. The complexity of the parts that can be made in this way is constrained by the lack of ductility in a continuous fibre prepreg. To introduce ductility into UD prepregs it is necessary to convert the continuous fibre to discontinuous form. Previous attempts using chopped or stretch-broken fibres for this purpose, which have met with limited success, will be briefly discussed and compared with the use of laser micro-perforation to convert existing qualified UD prepregs to discontinuous form, thereby retaining much of the mechanical performance of highly aligned continuous reinforced systems. The Perform laser process modifies the UD pre-preg by using highly focused laser pulses to cut the fibres into a series of 'fibre-domains' that undergo rearrangement whilst the part is being formed. The significance of the resulting 'fibre-domain' structure, with regard to the moderate "tensile knock-downs" and the low peak yield stresses observed during the drawing of these laser treated materials, will be explained. Data comparing the tensile and drawing properties of treated and untreated thermoplastic and thermoset systems will be presented. The results of limited forming trials using these ductile materials are also reported.