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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.10, #1)
Simplified Method for Prediction of Transient Hygroscopic Stresses in Polymer Matrix Composites with Symmetric Environmental Conditions by A. Tounsi; E. A. Adda-Bedia (pp. 1-18).
The purpose of this paper is to develop a direct and sufficiently exact method, which is much simpler than a numerical method, for computing of transient hygroscopic stresses in composite laminated plates. In references it has been shown that the calculation of moisture concentration inside laminated plates is necessary to compute the transient hygroscopic stresses and consequently we are bound to proceed calculating them each time in order to analyse these stresses. The developed method in this paper permits us to determine directly the values of such stresses without the calculation of the moisture concentration through laminated plates. In fact the series expressed by Equations (16) and (17) show that we are not in need of knowing the distribution of moisture concentration through laminates. Several examples are presented to demonstrate the assessment and performance in this method where we verified its accuracy by obtaining results for some laminates and comparing them with results from classical methods. Some stacking sequences exhibit important stresses within the plies which have to be taken into account in the design of composite structures submitted to a moist environment.
Keywords: polymer matrix composites; moisture concentration; transient hygroscopic stresses; composite laminated plates
E-Glass/Vinylester Composites in Aqueous Environments – I: Experimental Results by V. M. Karbhari; S. Zhang (pp. 19-48).
2- and 4-layered specimens of E-Glass/Vinylester fabricated from uniaxial, biaxial, and triaxial, non-woven fabrics processed using the resin infusion process are immersed in deionized water at 23 °C (73 °F) and 60 °C (140 °F), and a potassium based pH 10 buffer at 73 °F, for a period of 57 weeks in order to investigate durability in aqueous environments. It is shown that the coefficients of apparent diffusion and levels of moisture gain are the highest for the deionized water immersed samples at 60 °C (140 °F), and this results in the highest levels of tensile strength and modulus degradation. Tensile tests show the presence of an aqueous medium based post-cure that competes with the conventionally recognized mechanisms of deterioration in the resin, at the level of the fiber-matrix interface, and in the fiber, resulting in a retardation of absolute level of effects. It is also shown that effects of the immersion are different in the warp and fill directions and can in fact be affected by intricacies of the fabric architecture and thickness. It is shown that damage takes place through interface debonding and degradation as well as fiber pitting, and cracking, each of which serve as the means for renewed absorption of water resulting in moisture uptake at levels above the initial plateau. Effects of immersion on short-beam-shear strength and glass transition temperature are also elucidated.
Keywords: E-glass; vinylester; fabric architecture; resin infusion; fiber cracking; interphase degradation; pitting
Studies of Scale Effects for Crash on Laminated Structures by D. Dormegnie; D. Coutellier; D. Delsart; E. Deletombe (pp. 49-61).
This work proposes the study of the influence of scaled down ply layout techniques applied in a laminated composite structure submitted to fast dynamics. By its wide-ranging advantages, scale reduction represents a significant stake for engineers. An experimental campaign is carried out on an omega-shaped structure. The energies absorbed, as well as the efforts applied in the composite structure are then compared between the scale 1 prototype with the various models established (scales 1/2 and 1/4). The conclusions generated are numerous. Firstly, in this geometrical configuration, dynamic loading does not have the same effects on the results and, secondly, the relations of similitude used seem to be able to give some solutions, if the same ruin damage modes appear.
Keywords: composite material; dynamic; scale reduction; experimental campaign