AUTEX Research Journal, Vol. 7, No3, September 2007 © AUTEX http://www.autexrj.org/No3-2007/0252.pdf 166 COMPRESSIVE PROPERTIES OF STRETCH-BROKEN CARBON FIBRE (SBCF)/POLYAMIDE 12 COMMINGLED UNIDIRECTIONAL COMPOSITES Dr. Eng. Hisham A. Azzam Visiting Scientist, Concordia Center of Composite Material (CONCOM) Mechanical and Industrial Engineering Department, Concordia University, Montréal, Canada. e-mail: hishamiec@yahoo.com Abstract The present work investigates the compressive properties of SBCF/PA12 commingled unidirectional composites manufactured by the hot compression moulding technique. Different forms of failure mechanism have been observed microscopically for different laminate thicknesses (6, 8, 10, and 12 layers). In addition, fibre-length distribution curves have been developed at failure points. Thus, failure explanations for the SBCF/PA 12 composite during the compression test could be developed, depending upon microscopic observations. Moreover, the effect of laminate thicknesses on compressive behaviour; stress, strain and modulus has been analysed. It was found that by increasing laminate thickness the compressive stress is decreased, the strain is increased and the modulus is decreased significantly. Key words: thermoplastic, unidirectional reinforcement, compressive, CF/PA 12, stretch-broken filament. 1. Introduction Thermoplastic composite materials have received much interest for structural applications over the last 40 years, particularly in the aerospace field. Advanced thermoplastic composites (ATC) have recently been introduced as structural composite materials for high-performance aerospace applications [1]. Among the available thermoplastic polymers, polyamide (PA) is considered a good candidate as a thermoplastic composite matrix, mainly due to its low cost and easy handling [2]. Nowadays, efforts have been made to improve the knowledge related to the main factors that affect the interface properties and allow the intrinsic weakness of the polymeric composites to be overcome, namely interlaminar crack propagation. Concerning the particular case of standard carbon fibre/epoxy composite, it has been verified that its major weakness is related to poor resistance to delamination, due to the brittle nature of the thermoset matrix. As a consequence of such behaviour, studies in composite science have been carried out aimed at producing composite systems for which the matrix phase presents higher toughness values. These studies have been directed towards modifying thermoset matrices or developing tougher and more ductile matrices, most notably by using thermoplastic materials [3,4,5]. This complex compressive behaviour is very characteristic for fabric reinforced composites, and may have its origins in the initial material deformation (yarn crimp) caused before material impregnation and consolidation. Initial yarn crimp combined with manufacture-induced deformation as fibre misalignment in interlaced layers may lead to instantaneous and catastrophic compressive failure [4,5]. Thus, the nature and sequence of failure mechanisms occurring in textile composites during compressive loading is difficult to observe, and it has not so far been fully elucidated [6]. Lightweight, polymer matrix composites (PMCs) are enabling materials for aircraft which provide a combination of high stiffness-to-weight ratio, as well as improved corrosion and fatigue resistance. However, PMCs are expensive to manufacture. Considerable savings could be achieved by using lower cost composite forming, compression moulding, or other automated fabrication processes. The