Fatigue Behavior of Short Glass Fiber Reinforced Polyamide 66: Experimental Study and Fatigue Damage Modelling

Abstract

The aim of the present paper is to study and model the fatigue behavior of short glass fibers reinforced polyamide-66. The effect of fiber content on the fatigue and static behavior of this composite is investigated. In such composites fatigue damage growth exhibits three stages. A continuum damage based model is presented to predict damage evolution during these three stages. Experimental results show that increasing the fiber content increases the elastic modulus and the tensile strength of the studied materials under tensile tests. However, the rupture behavior changes from ductile to brittle. Moreover increasing the fiber percentage changes the S-N curves slope and decreases the fatigue life. Analytical results predicted by the proposed model, compared to experimental ones shows good agreement and the developed model predicted fatigue damage growth in its three stages of evolution with good performance. IntroductionThe use of short fibre reinforced thermoplastic composites is rapidly growing, because of their high specific properties. Their good mechanical and chemical properties, low weight and ease of processing in complex forms would make them a reliable substitute for metallic materials. Moreover, fibre composite materials are used in automotive applications, under the hood where environmental conditions are very severe.Large number of mechanical components are subjected to cyclic loading in their real operating conditions, which may causes fatigue failure even for loading levels below the elastic limit of the material. Therefore, the knowledge of the fatigue behaviour and mechanical properties of composite materials is vital, to optimize the design, to ensure the reliability and to guarantee the safe service use of components made of these materials. However, short glass fibre reinforced polyamide (PA-GFs) are very inhomogeneous since their mechanical properties result from the combination of the matrix, the glass fibres and of the interface (matrix/glass fibre) properties. Consequently, the mechanical behaviour of PA-GFs is a quite complex phenomenon since it is influenced by a large number of loading and structural parameter. Their mechanical properties are governed by the diameter, the length, the orientation and the quantity of fibres [1,2]. Also processing conditions: speed and pressure of injection and temperature of the mould may affect the behaviour of composite material [3]. Experimental variables (deformation speed, test temperature, frequency, etc.) have an important influence on the fatigue behaviour of these materials [4][5][6][7]. Environmental conditions such, as temperatures and humidity are very important consideration. In the open literature, the effect of several parameters on the fatigue behaviour of PA-GFs was studied.Several early studies have dealt with the influence of ambient temperature on the fatigue behaviour of PA66-GFs. It was shown that ambient temperature effect is related to the glass transition temperature (Tg) of the studied material. Handa et al. [8], demonstrated that...

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