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Design of a Flexible Skin for a Shear Morphing Wing

机译:剪力变形机翼的柔性蒙皮设计

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This article focuses on flexskins comprising of a cellular substructure and pre-tensioned facesheet for shear morphing applications. The unit cell of the substructure is a strand with some strain-relief feature, and it supports a segment of pretensioned facesheet. The function of the strain-relief feature is to reduce the peak strains in the strand and consequently the actuation work during shear morphing. Central hexagonal cells, elliptical cells, and half elliptical cells in the strand provided the sought strain relief at the edges of the strand, but the sharp corners and the proximity of these central features to those from adjacent strands during shear morphing led to a tendency for the facesheet to wrinkle. Alleviating wrinkling by increasing facesheet pretension increases the morphing actuation work requirement. Facesheet wrinkling can also be reduced by increasing strand separation, but this too requires higher prestrain in the facesheet to limit out-of-plane displacement under aerodynamic loads. The best solution was found to be the use of Gaussian- or Cosine-shaped curved strands which reduced morphing actuation force requirements by around 30% compared to straight strands used on a previous demonstration aircraft, and the peak strain levels to about 1.2% (down from 3.3% for straight strands), while avoiding facesheet wrinkling. Going from a unit cell to a finite strip accounting for boundary effects it was observed that the curved strands near the rigid boundaries of the skin panel come very close to the boundaries at high morphing angles, promoting wrinkling in the facesheet. A gradient reduction in the amplitude of the curved section along the length of a strip of flexskin approaching the problematic boundary alleviates this situation. Other approaches examined prior to the adoption of the smooth curved strands, such as selective bonding of facesheet to the strands, varying the strand thickness, or offsetting the central strain relieving feature between successive strands, were unable to eliminate face-sheet wrinkling at shear morphing angles.
机译:本文重点介绍由细胞亚结构和预张紧的面板组成的柔性皮肤,用于剪切变形应用。子结构的晶胞是具有某些应力消除特征的钢绞线,它支撑一段预张的面板。应力消除特征的功能是减少钢绞线中的峰值应变,从而减少剪切变形过程中的驱动工作。股线中的中心六角形单元,椭圆形单元和半椭圆形单元在股线的边缘提供了所需的应力释放,但是在剪切变形期间,尖角和这些中心特征与相邻股线的邻近特征导致了趋向于面板出现皱纹。通过增加面板张紧度来减轻皱纹增加了变形致动工作的需求。还可通过增加股线间距来减少面板起皱,但这也要求面板中具有更高的预应变以限制在空气动力载荷下的平面外位移。发现最好的解决方案是使用高斯形或余弦形弯曲线束,与以前的示范飞机上使用的直线束相比,变形驱动力要求降低了约30%,峰值应变水平降低到约1.2%(下从3.3%的直股),同时避免面板起皱。从一个晶胞到一个考虑边界效应的有限条带,可以观察到,在皮肤面板的刚性边界附近的弯曲股线在高变形角处非常接近边界,从而促进了面板中的起皱。沿着弯曲的带的长度接近问题边界的弯曲部分的振幅的梯度减小减轻了这种情况。在采用光滑弯曲线材之前,还检查了其他方法,例如面板与线材的选择性粘合,改变线材厚度或抵消连续线材之间的中心应变消除特征,这些方法都无法消除剪切变形时的面板皱纹。角度。

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