Effect of Hygrothermal Ageing on the Monotonic and Cyclic Loading of Glass Fiber Reinforced Polyamide Nader Haddar, 1 Imen Ksouri, 1 Tasnim Kallel, 2 Nizar Mnif 2 1 Laboratoire g  enie des mat  eriaux et environnement (LGME), ENIS, BP 1173-3038, Universit  e de sfax, Tunisia 2 Laboratoire Eau Energie et Environnement (L3E), ENIS, Universit  e de Sfax, Tunisia The properties of short glass fiber reinforced thermo- plastic based on polyamide 6 in humid environment are studied. Conditioning was conducted at 90  C. The combined action of water and heat (90  C) affects pro- gressively the mechanical properties. When the injec- tion molded samples were subjected to moisture, decrease in tensile strength and elastic modulus was observed whatever in distilled water or in salt solution. However, there is an enhancement of elongation at break with increasing exposure to humidity. After immersion in water, the fatigue life time is drastically reduced. Scanning electron microscope (SEM) was used in order to examine the fractured samples fea- ture. Results show that water diffuses into the polymer leading to a reduction of the interfacial stress trans- missibility. The major contributor of the stiffness loss is the adhesion loss between the fibers and the polymer. POLYM. COMPOS., 35:501–508, 2014. V C 2013 Society of Plastics Engineers INTRODUCTION Nowadays composite materials based on glass fiber are widely used. Owing to their particular properties (stiff- ness, toughness and resistance to dynamic fatigue), poly- amide composites are used in many fields especially in automotive industry such as interior accessories and under hood applications. Thus, the prediction of the durability of such materials is a very important issue for designers and users. It sustains several loads and different types of environmental conditions that attribute to its ageing in its particular environment. According to the severity of these conditions (high and/or low temperatures, water attack, UV exposure, saline atmosphere), different mechanisms may occur sepa- rately or simultaneously and decrease the performance and durability of composite materials. The presence of water in composite materials affects their physical, mor- phological, and mechanical properties and consequently their efficiency. Recently there has been a spate of inter- est in hygrothermal ageing on the mechanical behavior of composites materials. It has been shown that the moisture absorption rate depends on the matrix [1], fiber surface treatment [2], the nature of liquid that samples are put on [3] and temperature of conditioning [1, 4, 5]. In their study of thermoplastic composites, Bergeret et al. [1], revealed that sorption mechanism vary with the polymer matrix. They noted that the higher water uptake values were obtained for polyethylene terephtalate (PET) composites in comparison with polybutylene terephtalate (PBT) composite at the same temperature. When we talk about the effect of hygrothermal ageing we should not neglect the extent of fiber surface treat- ment. This fact was established by Bergeret et al. [2]. They found that using a specific treatment increases the water resistance of composites conditioned in aggressive environment. Nevertheless, absorption rate depends also on the nature of liquid that samples are put on. It has been shown that sorption behavior is not the same for samples placed in different fluids. Liao et al. [3] found that the mass increase in the materials depends on the type of fluid (water, 5% salt solution or 10% salt solution). Otherwise, temperature of conditioning has a crucial effect on the absorption mechanism. Thus, Bergeret et al. [1] showed that the diffusivity of water within the poly- mer matrix is easier and faster at high temperature. Like- wise, in a comparison of the diffusion coefficient at 20  C and 70  C, Vlasveld et al. [4] found a difference of roughly 17 times smaller at 20  C than at 70  C. In order to highlight the temperature effect during moisture age- ing, Ray [5] denoted that temperature acts like an activa- tor of the diffusion of the water molecules through the composite. Plasticization and hydrolysis are the adverse conse- quence of water absorption [5]. Polyamide 6 is known to be hygroscopic. Placed in humid condition, water can interpenetrate between amine and carbonyl as explained by Regrain [6]. Vlasveld et al. [4] found also that water Correspondence to: Imen Ksouri; e-mail: imen.ksouri@gmail.com DOI 10.1002/pc.22688 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2013 Society of Plastics Engineers POLYMER COMPOSITES—2014