Mechanical properties of long-fibre thermoplastic composites with laser drilled microperforations 1. Effect of perforations in consolidated material

A study is presented concerning a novel technique for enhancing the formabi lity of long-fibre thermoplastic composites. A laser beam has been used to drill arrays of holes into PEEK/AS-4 and PPS/AS-4 carbon-fibre composite pr e-preg. These arrays were designed to cut all the fibres to pre-determined lengths. Holes were of the order of 150 mu m in diameter, with average fibr e length reduced to either 20, 50 or 100 mm. Once perforated, the pre-preg material was consolidated into laminates in an autoclave. Tensile testing h as been used to evaluate the effects of the laser drilling. Experimental da ta show that the perforation process does not affect the stiffness, but str ength is reduced somewhat. This reduction is dependent on the distribution of holes and the nature of the laminate. The strength of notched laminates was found to be unaffected by perforation. Off-axis testing has been used t o evaluate the transverse and shear strength of both PEEK- and PPS-based co mposites, and this has been linked to observed failure mechanisms. Finite e lement modelling has been used to confirm that shear failure parallel to th e fibres is initiated by the stress concentrating effect of the perforation s. (C) British Crown Copyright 1999, DERA. Published by Elsevier Science Lt d with permission.