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Aging was carried out by introducing the materials into a climatic chamber under appropriate conditions of temperature, humidity and time. The materials are made of two types of weaving (2/2 Twill, 8H Satin) glass fibre, and (8H Satin) carbon fibre. The matrix was polyetherimide(PEI). In order to characterize the interlaminar fracture a mechanical test was carried out using the mode I Double Cantilever Beam (DCB) and mode II End Notched Fixed (ENF) tests. The analysis consists of knowing the different failure mechanisms which have generated the hygrothermal aging.En este trabajo se realiza un estudio sobre la influencia del envejecimiento higrotérmico en el comportamiento a fractura interlaminar de tres tipos de compuestos, dos de ellos reforzados con tejido de fibra de vidrio(2/2 Twill, y 8H Satin) y otro con fibra de carbono (8H Satin) . El envejecimiento se realizó manteniendo, durante diferentes periodos de tiempo, probetas en una cámara climática bajo unas determinadas condiciones de temperatura y humedad relativa. La determinación de la tenacidad a fractura interlaminar se realizó utilizando probetas de modos I (DCB) y II (ENF). El análisis realizado consistió en poner de manifiesto los diferentes mecanismos de rotura a fractura que se generan tras someter las probetas a la exposición higrotérmica. De los resultados de los ensayos se concluye un diferente comportamiento a fractura según el refuerzo existente y también a igual refuerzo, según la trama del tejido.

The mechanical behavior of a composite with thermoplastic matrix and glass fiber reinforcement has been studied. It has been tested to constant stresses of a value equivalent to tensile strength divided by three to 50, 100 and 150 ºC, during periods of time between 250 and 3000 minutes. A decrement of the tensile strength and deformation can be observed in the three temperatures. Also a group of specimens have been exposed to accelerated aging in an environmental chamber to 70 ºC and 95% RH, during 30 days; and after they have been tested. In that case a decrement of the strength and deformation after 250 minutes has been observed, but in larger time of exposure these properties suffered an increment.Se ha estudiado el comportamiento mecánico de un compuesto fabricado con un termoplástico PEI (polieterimida) reforzado con tejido de fibra de vidrio, frente a ensayos en los que se mantienen tensiones iguales a un tercio de su resistencia a tracción a 50, 100 y 150 ºC, durante periodos comprendidos entre 250 y 3000 minutos. En los resultados se observa una disminución de la resistencia y de la deformación en las tres temperaturas, con un mantenimiento de sus valores hasta las ensayadas a 3000 minutos. Además fueron expuestas un grupo de probetas del material, a envejecimiento acelerado en cámara higrotérmica a 70 ºC y a un 95% de H.R., durante 30 días; para luego someterlas a los ensayos antes descritos. Para esas probetas se obtuvieron pequeñas fluctuaciones de la resistencia y deformación con el tiempo, sin observarse una influencia significativa de la temperatura a la que se hicieron los ensayos termomecánicos.

The strain energy rate of three woven fabric reinforced thermoplastic composites is presented. The delamination energy of the two materials, glass fiber weave (2/2 Twill, 8H Satin) and a carbon fiber (8H Satin), is compared to study the effect of weave and reinforcement on mechanical properties.

Natural continuous natural fibres (hemp, flax, etc.) are gaining popularity in composite materials because they can advantageously replace glass fibers. It is found that intrinsic properties of unidirectional (UD) composites are almost equivalent to those of unidirectional glass fiber composites. Unfortunately it is difficult to get repeatable results because of the inherent variability in the properties of natural fibers compared to glass fibers. Their quality is largely affected by the weather conditions, the extraction location along the plant and the techniques used to extract them (retting, bleaching, etc.). The present paper proposes a strength reliability model for unidirectional composites with natural fibers in a hexagonal array. The model assumes that, a central core of broken fibers flanked by unbroken fibers which are subject to stress concentrations from the broken natural fibers. Thermal and hygroscopic residual stresses are neglected because they haven't more effect when the composite was subjected to tensile than transverse loading. The approach of the model consists of using a modified shear lag model to calculate the ineffective lengths and stress concentrations around the broken fibers. In this paper, we attempt to incorporate in the proposed model the unidirectional composite property variation with temperature and moisture in order to predict even composite strength degradation. Strength degradation is often seen as a result of changes in ineffective lengths at natural fiber breaks and the corresponding stress concentrations in intact neighboring fibers. [ABSTRACT FROM AUTHOR]

This article addresses the experimental characterization of the abrasive wear of two woven fabric carbon fiber and glass fiber composite materials, taking into account the effect of moisture absorption. The composite materials were tested to three level loadings and two sliding speeds. The abrasive used was dry sand of size 0.6 µm, and the time of wear testing was 10 min. In order to study the effects of moisture on wear behavior, another series of samples was introduced into the tank of water during a period of 40 days at ambient temperature. The planning design experimentation approach was applied to obtain a mathematical model taking into account the influencing parameters on the wear behavior of the composites. The wear results have shown that for a higher turn speed and a load, the loss of matter increases. In the case of samples exposed to water absorption, the wear rate increases more than the dry samples. The micrographs of the surface of the samples tested were taken in order to characterize the wear mechanism. [ABSTRACT FROM PUBLISHER]

Composite materials posses better characteristics and properties and therefore have wider application in industry. However, their development relies on a better understanding of their mechanical behavior. The aim of this article is to investigate the behavior of a thermoplastic material matrix composite reinforced by glass fabric type RT270 to break under temperature variation. Resilience tests were applied on standard notched specimens (cuts made in two directions over the layers, and mutually perpendicular) precracked from notch depth, with fibers direction being 0°/90° and +45°/-45°. Different temperatures have been used for each type (-30°, 0°, 30°C). These tests were developed following a designed experience of type 23.31, requiring 24 experiments performed in triplicate. Through regression analysis, a mathematical model describing the tensile strength according to the influential parameters is obtained, and the results of the tests allow calculating the strength (energy). From the results obtained, it was observed that energy is also important in the case of an edge notch in the front side and that the fibers direction and temperature variation have a great influence on the impact resistance and sensitivity of composite material. [ABSTRACT FROM AUTHOR]

This article addresses the experimental characterization of the mechanical properties of three types of woven fabric composites taking into account the effects of hygrothermal and hygrothermomechanical aging. Characterization was carried out using the mode I, double cantilever beam (DCB) and the mode II, end notched flexural (ENF) interlaminar fracture tests in order to determine the loss in crack propagation resistance. The materials used were two types of woven (2/2 Twill, 8-Harness Satin) glass fiber, and 8-Harness Satin carbon fiber. The matrix was polyetherimide (PEI). The critical values of the energy release rate in mode I and mode II were calculated using the corrected beam theory. The material reinforced with 8-Harness Satin glass fiber presented the best behavior in mode I and mode II. The decrease in fracture strength is more important in the material reinforced with carbon fiber. [ABSTRACT FROM AUTHOR]

This work presents an analytical model to predict the strength of the unidirectional carbon epoxy composite using micromechanical techniques. This model supposes that a group of broken fibres surrounded by a number of intact fibres with hexagonal arrangement. The mathematical developments used are presented to justify the distribution form of the stresses around broken fibre and adjacent intact fibres. To follow the evolution of the damage in regions of debonding and local plasticity; we proceeded to a progressive increase in the fiber volume fraction and tensile external load. This, procedure enable us to evaluate the extension of the region locally plasticized, the ineffective region, the stress concentration and the longitudinal displacement of broken and intact fibres, in function of broken fibres number and specimen length. As fiber breaks are intrinsically random, the variability of input data allows us to describe the probabilistic model by using the Monte-Carlo method. The sensitivities of the mechanical response are evaluated regarding the uncertainties in design variables such as Young’s modulus of fibers and matrix, fiber reference strength, shear yield stress, fiber volume fraction and shear parameter defining the shear stress in the inelastic region.