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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.10, #6)
Selection of Optical Fibers Paths and Sensor Locations for Monitoring the Integrity of Composite Patching by George J. Tsamasphyros; George N. Kanderakis; Nikos K. Furnarakis; Zaira P. Marioli-Riga; Roland Chemama; Rene Bartolo (pp. 331-338).
In order to select appropriate optical fiber paths and locations for Bragg Grating sensors, the research group has studied a classically cracked metallic structure repaired with a ‘smart’ bonded composite patch using finite element analysis. The patch was bonded over a cracked aluminum plate by means of a thin adhesive layer. The primary loading axis of the metal was assumed parallel to the direction of the optical fibers used. A variety of optical fiber paths and sensor positions was considered, along with their ability to measure the developed strain field and to trace the position of the crack tip. It was concluded that a fiber optics network is indeed capable of tracing effectively the critical parameters required for the monitoring of structural integrity of the composite patch-reinforced structures (i.e. strains developed at the patch and at the tip of the crack). It was found that at least two Bragg Grating sensors should be used at each side of the crack per optical fiber, in order to enable adequate monitoring of the strain field and the position of the crack tip. Different locations should be chosen according to the configuration of the patch (one or two-sided).
Ellipticity Ratio Effects in the Energy Absorption of Axially Crushed Composite Tubes by O. M. S. Alkoles; E. Mahdi; A. M. S. Hamouda; B. B. Sahari (pp. 339-363).
In this paper, the influence of ellipticity ratio on energy absorption capability and load-carrying capacity of woven roving wrapped composite elliptical tubes has been investigated both experimentally and numerically. A series of experiments was conducted for composite elliptical tubes with ellipticity ratios (a/b) ranging from 1 to 2. Typical failure histories of their failure mechanism are presented and discussed. The experimental data are correlated with predictions from a finite element model. Load-deformation curves and deformation histories of typical specimens are presented and discussed. For all specimens considered, classical axial collapse eigenvalues were computed. The results showed that the ellipticity ratio significantly influenced the energy absorption capabilities as well as the load-carrying capacity. Tubes with ellipticity ratios of a/b 1.25 and 2.0 displayed the highest normalised specific energy absorption capability. A reasonable agreement between the experimental and computational results was obtained for the critical crush load.
Keywords: composite tubes; ellipticity ratio; energy absorption capability; load-carrying capacity; failure mechanism
Wood Fibre Reinforced Polypropylene Composites: Effect of Fibre Geometry and Coupling Agent on Physico-Mechanical Properties by Andrzej K. Bledzki; Omar Faruk (pp. 365-379).
Wood fibre reinforced polypropylene composites at fibre content 50% by weight have been prepared and different types of wood fibres (hard wood fibre, soft wood fibre, long wood fibre and wood chips) were treated with coupling agent (MAH-PP) to increase the interfacial adhesion with the matrix to improve the dispersion of the particles and to decrease the water sorption properties of the final composite.The present study investigated the tensile, flexural, charpy impact and impact properties of wood fibre reinforced polypropylene composites as a function of coupling agent and fibre length and structure.From the results it is observed that wood chips-PP composites showed better tensile and flexural properties comparative with the other wood fibre-PP composites with the addition of 5%MAH-PP, which is around 65% and 50% for tensile strength and flexural strength respectively. Hard wood fibre-PP composites showed better impact characteristic values comparative to other wood fibre-PP composites with the addition of 5%MAH-PP and damping index decreased about to 60%. Charpy impact strength also increased up to 60% with the addition of 5%MAH-PP for long wood fibre-PP composites. Water absorption and scanning electron microscopy of the composites are also investigated.
Keywords: wood fibre-polypropylene composites; maleated polypropylene; fibre length and geometry; mechanical properties; water absorption