Wind turbine blades continue to be the target of technological improvements by the use of better designs, materials, manufacturing, analysis and testing. As the size of turbines has grown over the past decade, designers have restrained the associated growth in blade weight to less than would have been possible through simple scaling-up of past approaches. These past improvements are briefly summarized. Manufacturing trends and design drivers are presented, as are the ways these design drivers have changed. Issues related to blade material choices are described, first for the currently dominant glass fibre technology and then for the potential use of carbon fibres. Some possible directions for future blade design options are presented, namely new planforms, aerofoils and aeroelastic tailoring. The significant improvement in sophistication of stress analysis and full-scale blade testing are also discussed.
This paper presents a study about the influence of through-thickness tufted fibres on compression and bending properties of sandwich structures. The tufting process aims to avoid the delamination between the skin and core in order to improve the performance of sandwich structures, increase the interlaminar strength and damage tolerance of sandwich structures.
To evaluate the effect of tufting in sandwich structures, an experimental study was developed which included edgewise compression and 3-P bending tests of tufted and nontufted sandwich panels made of carbon/epoxy and E-glass/epoxy face sheets, PVC and PUR foam cores and E-glass and aramid through-thickness fibres with different tufting densities.Conclusions about the efficiency of the insertion of through-thickness fibres on compression and bending properties are drawn.
The interlaminar tensile strength of carbon/epoxy laminated curved beams with variable thicknesses is experimentally studied by means of a four-point-bending test. Firstly, the relationships between the used formulae and the results obtained are analyzed on the curved beams with different thicknesses and tested in compliance with ASTM D6415 standard. Secondly, both the interlaminar tensile stresses and the post-failure behavior are determined. Finally, the critical area, where delamination begins, is reinforced through-the-thickness by means of tufting technology with different densities. The influence on the maximum interlaminar tensile stress as well as delamination evolution of the carbon/epoxy laminated curved beams are analyzed. These results play an important role in the prediction of interlaminar tensile strength and post failure behaviour of laminated curved beams.
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