Mechanical characterization and acoustic emission monitoring of damage mechanisms of flax/carbon hybrid fiber composites

L'utilisation de fibres naturelles comme renfort permet d'améliorer les performances environnementales des matériaux composites ainsi que leurs propriétés d’amortissement. Néanmoins, ces composites à fibres naturelles présentent des performances mécaniques moins intéressantes que celles des composites à fibres synthétiques. Dans ce contexte, cette étude propose d'élaborer des structures composites à renfort hybrides constituées des fibres de lin et de carbone. L’objectif de cette hybridation est de trouver un compromis entre les propriétés mécaniques et dissipatives. Tout d'abord, le comportement en statique des composites à fibres de lin, fibres de carbone et fibres hybrides lin/carbone a été analysé. Les caractéristiques élastiques principales d’ un pli UD en contraintes planes sont ainsi déterminées .Par ailleurs, un suivi et une analyse des mécanismes d'endommagement ont été effectués au moyen de la technique d'émission acoustique associée à des observations microscopiques. Dans un souci de mieux répondre aux besoins industriels, le comportement des composites soumis aux essais de fatigue cyclique doit être étudié. Pour ce faire, le comportement en fatigue de ces matériaux à renforts non-hybrides et hybrides a été analysé sous sollicitations de traction et de flexion trois points. L’ influence de l’ hybridation sur la durée de vie en fatigue de ces composites a été établie. Enfin, une étude expérimentale et une modélisation par élément finis du comportement vibratoire des composites non-hybrides et hybrides ont été réalisées. Ainsi, le rôle des différentes fibres, de l’orientations des fibres, de séquences d’empilement dans l'amortissement en vibrations a été discuté.The use of natural fibers as reinforcement makes it possible to improve the environmental performance of the composite materials as well as their damping properties. Nevertheless, these natural fiber composites have lower mechanical performance than synthetic fiber composites. In this context, this study proposes to develop composite structures with hybrid reinforcement made of flax and carbon fibers. The objective of this hybridization is to find a compromise between the mechanical and dissipative properties. First, the static behavior of flax fiber, carbon fiber and flax/carbon hybrid composites was analyzed. The principal elastic characteristics of a UD ply in plane stresses are thus determined. Moreover, a monitoring and an analysis of the mechanisms of damage were carried out by means of the technique of acoustic emission associated with microscopic observations. In order to better meet industrial needs, the behavior of composites subjected to cyclic fatigue tests must be studied. In fact, the fatigue behavior of these materials with non-hybrid and hybrid reinforcements was analyzed under tensile stress and three-point bending. The influence of hybridization on the fatigue life of these composites has been established. Finally, an experimental study and a finite element modeling of the vibratory behavior of non-hybrid and hybrid composites were carried out. Thus, the role of different fibers, fiber orientations, stacking sequences in vibration damping has been discussed

Caractérisation mécanique et suivi par émission acoustique des mécanismes d’endommagement des composites à fibres hybrides lin/carbone

The use of natural fibers as reinforcement makes it possible to improve the environmental performance of the composite materials as well as their damping properties. Nevertheless, these natural fiber composites have lower mechanical performance than synthetic fiber composites. In this context, this study proposes to develop composite structures with hybrid reinforcement made of flax and carbon fibers. The objective of this hybridization is to find a compromise between the mechanical and dissipative properties. First, the static behavior of flax fiber, carbon fiber and flax/carbon hybrid composites was analyzed. The principal elastic characteristics of a UD ply in plane stresses are thus determined. Moreover, a monitoring and an analysis of the mechanisms of damage were carried out by means of the technique of acoustic emission associated with microscopic observations. In order to better meet industrial needs, the behavior of composites subjected to cyclic fatigue tests must be studied. In fact, the fatigue behavior of these materials with non-hybrid and hybrid reinforcements was analyzed under tensile stress and three-point bending. The influence of hybridization on the fatigue life of these composites has been established. Finally, an experimental study and a finite element modeling of the vibratory behavior of non-hybrid and hybrid composites were carried out. Thus, the role of different fibers, fiber orientations, stacking sequences in vibration damping has been discussed.L'utilisation de fibres naturelles comme renfort permet d'améliorer les performances environnementales des matériaux composites ainsi que leurs propriétés d’amortissement. Néanmoins, ces composites à fibres naturelles présentent des performances mécaniques moins intéressantes que celles des composites à fibres synthétiques. Dans ce contexte, cette étude propose d'élaborer des structures composites à renfort hybrides constituées des fibres de lin et de carbone. L’objectif de cette hybridation est de trouver un compromis entre les propriétés mécaniques et dissipatives. Tout d'abord, le comportement en statique des composites à fibres de lin, fibres de carbone et fibres hybrides lin/carbone a été analysé. Les caractéristiques élastiques principales d’ un pli UD en contraintes planes sont ainsi déterminées .Par ailleurs, un suivi et une analyse des mécanismes d'endommagement ont été effectués au moyen de la technique d'émission acoustique associée à des observations microscopiques. Dans un souci de mieux répondre aux besoins industriels, le comportement des composites soumis aux essais de fatigue cyclique doit être étudié. Pour ce faire, le comportement en fatigue de ces matériaux à renforts non-hybrides et hybrides a été analysé sous sollicitations de traction et de flexion trois points. L’ influence de l’ hybridation sur la durée de vie en fatigue de ces composites a été établie. Enfin, une étude expérimentale et une modélisation par élément finis du comportement vibratoire des composites non-hybrides et hybrides ont été réalisées. Ainsi, le rôle des différentes fibres, de l’orientations des fibres, de séquences d’empilement dans l'amortissement en vibrations a été discuté

A New PSO-based Algorithm for Two-Dimensional Non-Guillotine Non-Oriented Cutting Stock Problem

In this paper, a new algorithm is proposed for the two-dimensional non-guillotine non-oriented cutting stock problem. The considered problem consists of cutting small rectangular pieces of predetermined sizes from large but finite rectangular plates. The objective is to generate cutting patterns that minimize the unused area and fulfill customer orders. The proposed algorithm is a combination of a new particle swarm optimization approach with a heuristic criterion inspired from the literature. The algorithm is tested on twenty-two instances divided into two sets. Corresponding results show the algorithm efficiency in optimizing the trim loss that is comprised between 2.6% and 7.8% for all considered instances

Middle to late Holocene sedimentary filling history of the Sebkha el Melah in south-eastern Tunisia

peer reviewedThe sedimentological and geochemical properties of a 146 cm long sediment core collected from Sebkha el Melah (Ml core) in south-eastern Tunisia have been used to infer the genesis and evolution of the Sebkha el Melah over the last 5000 years. Two main sedimentary units have been defined: a huntite [Mg3Ca(CO3)4] unit at the bottom of core Ml is covered by a second unit made up of siliciclastic and evaporitic materials. The huntite level is synchronous with Holocene marine transgression, which was followed by a regression of about 5300 years bp. Geochemical data (major and trace element), magnetic analyses, grain-size distribution and microtexture of quartz grains were performed to assess the sediment provenance. The upper unit of Ml core is characterized by alternations between fluvial, aeolian and evaporite deposits. Redox proxies displaying marked Fe/Ca and Rb/S peaks, in addition to high magnetic susceptibility (MS) values, polymodal grain-size frequency curves, as well as sub-angular grains with V-shaped percussion cracks, are suggestive of palaeohydrological events. In contrast, a decreasing trend in the low MS values, bi-modal grain-size frequency curves as well as well-rounded quartz grains with crescent percussion marks would indicate enhanced aeolian sand input in the sebkah el Melah sequence. Moreover, geochemical proxies suggest formation of evaporite facies under a strongly warm climate contemporary with marine intrusion

Damage mechanisms assessment of hybrid carbon/flax fibre composites using acoustic emission

The purpose of the present experimental study is to describe the damage mechanisms occurring in epoxy matrix composites reinforced with hybrid carbon-flax fibres. The samples tested were consist of unidirectional carbon and flax fibre plies with different stacking sequences. Composite laminates were manufactured by hand lay-up process. The specimens were tested under uniaxial tensile loading. The tests carried out were monitored by the acoustic emission (AE) technique. The results obtained during the monotonic tensile tests were analyzed in order to identify the damage mechanisms evolutions. The recorded events were classified with the k-means algorithm which is a statistical multivariable analysis. In addition, it was an unsupervised classification according to temporal descriptors. The percentage of each damage mechanism to the global failure was evaluated by the hits number and the acoustic energy activity. The AE technique was correlated with scanning electron microscopy (SEM) observations to identify the typical damage mechanisms

Effet de l'hybridation sur les propriétés mécaniques et vibratoires des composites à fibres lin-carbone

International audienceIn recent days, several industries are focus on the light weight and environmentallyfriendly materials with good mechanical and damping properties.Flax fiber reinforced composites have been proven in the field of dynamics with high vibration damping performance. Nevertheless, their static mechanical and fatigue characteristics are much less important than composites made of carbon fibers.To overcome these problems, hybridization technique of flax fibers and carbon fibers is used to manufacture compositesto enhance their properties.Therefore, the objective of this study is to investigate the effect of hybridization on the mechanical and vibratory behavior of composites.Two types of non-hybrid laminates (flax / epoxy and carbon / epoxy) and different hybrid laminates (flax / carbon / epoxy) have been experimentally characterized. At first, the different composite laminates were studied using uni-axial tensile tests. In a second step, an experimental modal analysis was conducted to identify the damping coefficients experimentally.Ces derniers jours, plusieurs industries se sont concentrées sur les matériaux légers et écologiques, dotés de bonnes propriétés mécaniques et amortissantes.Les composites renforcés de fibres de lin ont fait leur preuve dans le domaine de la dynamique en présentant des performances élevées en amortissement des vibrations. Néanmoins, leurs caractéristiques mécaniques statiques et de fatigue sont nettement moins importantes que celles des composites constitués de fibres de carbone. Pour surmonter ces problèmes, la technique d'hybridation de fibres de lin et de fibres de carbone est utilisée pour fabriquer les composites afin d’améliorer leurs propriétés.De ce fait, l’objectif de la présente étude consiste à investiguer l’effet de l’hybridation sur le comportement mécanique et vibratoire des composites. Deux types de stratifiés non-hybride (lin/époxy et carbone/époxy) et différentes stratifiés hybrides (lin/carbone/époxy) ont été caractérisés expérimentalement.Dans un premier temps, les différents stratifiés composites ont été étudiés à l'aide des essais de traction uni-axiaux. Dans un deuxième temps, une analyse modale expérimentale a été menée afin d’identifier expérimentalement les coefficients d’amortissemen