Analysis of Failure Mechanisms and Hybrid Effects in Carbon Fibre Reinforced Thermoplastic Composites

摘要

First part of this thesis studies tensile failure mechanisms of unidirectional laminates made of carbon fibre reinforced thermoplastic composites. Global mechanical properties (such as 0° and 90° tensile strength), and microscopic mechanical properties (such as work of adhesion, matrix modulus, matrix residual stress, interfacial shear strength and interlaminar fracture toughness in mode II) are experimentally evaluated. Comparison of various prepreg systems using the same carbon fibre illustrates the characteristics of semi-crystalline polymer matrices including polypropylene, polyamide 6 and polyphenylene sulfide and their interfaces with carbon fibre. In addition, the impact of process conditions related to matrix crystallinity on each mechanical property is evaluated. Constitutive models, which describe the failure mechanisms of unidirectional laminates, are constructed using existent techniques, and contributions of fibre and matrix/interface related parameters are clarified. In addition, explanations to fill the gap between experiment and prediction of tensile strength are presented. They are comprised of a revised carbon fibre strength distribution in the range of small fibre length, the decrease of the matrix shear yield stress under tension and the generation of splitting prior to final failure.Second part of this thesis studies hybrid designs using the carbon fibre reinforced polypropylene and self-reinforced polypropylene. The hybrids achieve simultaneously high modulus/strength and excellent energy absorption under static tension. A synergy effect is observed in the initial modulus increase of self-reinforced polypropylene, which is induced by the suppression of its Poisson contraction by the carbon fibres. Furthermore, improvement of the Izod impact strength is achieved by changing the amount of tough self-reinforced polypropylene in the hybrids and with a modification of the interlayer.