考虑蠕变的变后掠翼柔性蒙皮光滑特性分析

Analysis of smooth characteristics of flexible skin for variable-sweep wing considering creep

关键词:  变后掠翼  柔性蒙皮  橡胶蠕变  硅橡胶表层  临界剪切角

Key words:  variable-sweep wing  flexible skin  rubber creep  silicone rubber surface layer  critical shear angle

摘要:

为满足剪切式变后掠翼在变形过程中的光滑连续性需求,提出了一种表层采用预拉伸硅橡胶作为维形层的柔性蒙皮结构。为保证该蒙皮在机翼后掠角变化范围内保持光滑连续,开展该蒙皮光滑褶皱临界剪切角研究。首先,基于表征蠕变行为的三参数固体模型及量纲归一化的分析方法,建立硅橡胶表层的黏弹性预测模型。其次,依据最小应力准则,建立了考虑硅橡胶表层黏弹性的临界模型,完成预拉伸柔性蒙皮临界剪切角的求解,并提出求解临界剪切角的经验公式。最后,采用有限元方法对不同预拉伸量的蒙皮临界剪切角进行了仿真分析,通过沿x方向和y方向施加位移产生拉伸变形,沿对角线方向施加旋转和位移产生剪切变形。研究结果表明,在大拉伸应变范围内,硅橡胶表层的黏弹性模型能够准确地描述硅橡胶静态蠕变行为,考虑硅橡胶表层黏弹性的预拉伸柔性蒙皮光滑性临界剪切角模型具有较高的精度；预拉伸量与硅橡胶表层的蠕变特性对临界剪切角具有显著影响,双向拉伸有利于提高蒙皮的抗褶皱能力,从而在变后掠过程中保持表面光滑性。理论预测结果与仿真结果、实验结果吻合良好,对剪切式变形后掠翼的工程应用具有较大价值。

Abstract:

To meet the requirement of smooth continuity during the deformation process of the shear-type variable-sweep wing, this paper proposed a flexible skin structure using pre-stretched silicone rubber as the shape-maintaining surface layer. To ensure that the skin maintains smooth continuity within the variation range of the wing sweep angle, this paper investigated the critical shear angle for skin smoothness and wrinkling. First, based on a three-parameter solid model characterizing creep behavior and a dimensionless normalization analysis method, this paper established a viscoelasticity prediction model of the silicone rubber surface layer. Second, according to the minimum stress criterion, this paper established a critical model considering the viscoelasticity of the silicone rubber surface layer, completed the calculation of the critical shear angle of the pre-stretched flexible skin, and proposed an empirical formula for solving the critical shear angle. Finally, this paper simulated and analyzed the critical shear angles of skins with different pre-stretching amounts using the finite element method, generated tensile deformation by applying displacements along the x and y directions, and generated shear deformation by applying rotation and displacement along the diagonal direction. The results indicate that within a large tensile strain range, the viscoelastic model of the silicone rubber surface layer can accurately describe the static creep behavior of the silicone rubber, and the critical shear angle model for the smoothness of the pre-stretched flexible skin considering the viscoelasticity of the silicone rubber surface layer has high accuracy; the pre-stretching amount and the creep characteristics of the silicone rubber surface layer have a significant impact on the critical shear angle, and biaxial stretching is beneficial to improve the anti-wrinkling ability of the skin, thereby maintaining surface smoothness during the variable-sweep process. The theoretical prediction results agree well with the simulation results and experimental results, which has great value for the engineering application of the shear-type variable-sweep wing.