Mechanical properties of long-fibre thermoplastic composites with laser drilled microperforations 2. Effect of prior plastic strain

An examination is presented of how the mechanical properties of a PPS-based carbon-fibre composite, in which an array of fine holes had been generated by laser drilling, are affected by the prior imposition of large plastic s trains. This was done in order to explore how a typical high temperature fo rming operation would be likely to change the microstructure of such microp erforated material and hence to affect its mechanical properties. Tensile s trains of up to 200% were imposed in a drawing operation, with imposed tran sverse constraint sufficient to ensure that the fibres remained within the plane of the specimen. After drawing, specimens were tested to failure in t ension at room temperature. It has been found that the strength and stiffne ss of the material remains relatively dose to the corresponding values prio r to deformation for strains of up to about 50%. Above this level, both str ength and stiffnesses were observed to decrease fairly rapidly. These resul ts have been explained in terms of the microstructural changes which accomp any the drawing process. (C) British Crown Copyright 1999, DERA. Published by Elsevier Science Ltd with permission.