基于稳定理论的剪切薄膜褶皱发展过程及其动力特性研究

发布时间：2018-06-07 23:09

本文选题：薄膜结构 + 褶皱　；参考：《北京交通大学》2013年博士论文

【摘要】：随着薄膜结构在建筑结构领域和航天器方面的大量应用,褶皱问题所带来的不利影响逐渐引起了人们的广泛关注。褶皱的出现不仅会影响到结构的表面精度,而且会改变结构的应力分布状况,影响结构的振动特性,并对风荷载作用下的气动特性产生不利影响。因此,必须对褶皱的形成特点和发展过程进行深入研究,从而掌握褶皱发展机理,及褶皱对薄膜力学性能的影响规律,以有助于对褶皱现象进行有效控制。虽然实际工程中薄膜结构的几何形状复杂多变,而平面张拉薄膜是一种形式最简单的薄膜结构,但通过对平面张拉薄膜的研究可以忽略次要因素,深入分析从薄膜结构中抽象出来的共性问题,揭示出在褶皱产生和发展过程中,结构力学性能的变化规律。因此,本文将以平面薄膜为研究对象,分析褶皱的产生和发展规律,以及对结构静力特性和动力性能的影响。本文在薄膜结构褶皱问题方面的研究工作,可以分为计算理论与数值分析两个方面： (1)计算理论方面：基于稳定理论,提出了考虑沿褶皱方向张拉应力的影响时,临界压应力的计算方法,并得到了波长和幅值等构形参数的表达式。通过与已有文献的试验结果和数值分析结果的比较,表明所得计算公式是合理有效的,并具有良好的精度。 (2)数值分析方面的研究工作,主要分为以下几个部分： a.提出并验证了将褶皱的产生和发展过程进行三阶段划分的思想。通过对褶皱产生和发展过程的研究发现：褶皱首先发生在压应力最早出现的部位,然后向中间部位扩展,最后达到稳定。因此,该过程表现为：初始阶段、扩展阶段和稳定阶段三个典型阶段,并对每一阶段的褶皱特点进行研究。通过对褶皱产生和发展过程的研究,可以认识褶皱机理,掌握褶皱对薄膜结构力学特性的影响规律。同时通过这种划分,能够有效地衡量褶皱发展程度,并方便地对处于特定状态的褶皱性状进行研究和描述。 b.提出并验证了褶皱控制临界值的思想,为防止结构因面外变形和褶皱数量的迅速增大(多)而失效提供量化依据。对剪切矩形薄膜进行仿真试验研究发现,当薄膜的面外位移达到膜材厚度的1%时,就必须对褶皱进行控制,否则结构的面外变形会迅速增大,而导致结构失效。 c.以薄膜厚度、张拉预应力、初始缺陷为关键参数,对其在褶皱产生和发展过程中的影响进行了研究。结果表明：随着薄膜厚度的增加,褶皱数量减少,幅值和波长变大,但面外位移与厚度的比值减小,因此厚度越小,褶皱对结构的不利影响越大；增大张拉预应力,可以延迟褶皱的出现,增强结构的面外稳定性,但是材料的强度安全储备会减少,因此应合理控制张拉预应力;初始缺陷主要影响到褶皱的位置,尤其是褶皱最先出现的位置,而对褶皱数量、波长、幅值等的影响不明显。 d.对褶皱发展不同阶段的结构动力特性进行了研究。结果表明：频率随剪切位移角的变化,也表现出三个典型阶段：初始阶段(频率下降),扩展阶段(频率波动上升)和稳定阶段(频率缓慢下降)。在稳定阶段,由于结构会发生二次屈曲,频率可能出现小幅波动。振型的变化与频率相比较为复杂,但总体趋势表现为与褶皱方向一致的振型增多。
[Abstract]:With the large number of applications of the film structure in the field of architecture and spacecraft, the adverse effects of the fold problem have gradually aroused widespread concern. The emergence of folds not only affects the surface accuracy of the structure, but also changes the stress distribution of the structure, the vibration characteristics of the structure and the wind load. The aerodynamic characteristics have adverse effects. Therefore, it is necessary to study the formation characteristics and development process of folds, so as to grasp the development mechanism of folds and the influence of folds on the mechanical properties of the thin films, so as to help control the folds effectively. Although the geometric shape of the thin film structure is complex and changeable in the actual project, the plane tension is made. Thin film is the simplest form of thin film structure, but by studying the plane tensioning film, the secondary factors can be ignored. The general problem abstracted from the thin film structure is deeply analyzed, and the change law of structural mechanical properties is revealed in the process of formation and development of folds. Therefore, this paper will take the plane film as the research object. The law of generation and development of folds, and its effects on static and dynamic properties of structures are also analyzed.
In this paper, the research work on membrane structure folds can be divided into two aspects: computational theory and numerical analysis.
(1) the calculation theory: Based on the stability theory, the calculation method of critical pressure stress is put forward in consideration of the influence of tensile stress along the fold direction, and the expressions of the parameters of the wavelength and amplitude are obtained. By comparing with the experimental results and the numerical analysis results of the existing literature, it is shown that the calculated formula is reasonable and effective. It has good precision.
(2) the research work in numerical analysis is mainly divided into the following parts:
A. puts forward and verifies the thought of dividing the formation and development of folds in three stages. Through the study of the process of formation and development of folds, it is found that the folds first occur at the earliest stage of compressive stress and then expand to the middle part, and finally reach stability. Therefore, the process is manifested in the initial stage, the expansion stage and the stability. In the three typical stages, the fold characteristics of each stage are studied. Through the study of the formation and development of folds, the mechanism of folds can be understood and the influence of folds on the mechanical properties of the membrane structures can be grasps. At the same time, the development degree of folds can be measured effectively and it is convenient to be in a specific state. The characters of folds are studied and described.
B. puts forward and validates the thought of the critical value of the fold control, which provides a quantitative basis for preventing the structure from increasing rapidly (more) and increasing the number of out of plane deformation and folds. A simulation test of the shear rectangular film shows that the fold must be controlled when the surface displacement of the film reaches 1% of the thickness of the film, otherwise the structure is outside the surface. The deformation will increase rapidly, which leads to the failure of the structure.
The influence of C. film thickness, tensioning prestress and initial defect as the key parameters on the formation and development of folds was studied. The results showed that the number of folds decreased, the amplitude and wavelength increased with the increase of film thickness, but the ratio of the displacement to thickness decreased, so the smaller the thickness, the adverse effects of folds on the structure. The larger the tensioning prestress can delay the emergence of folds and enhance the external stability of the structure, but the safety of the material will be reduced, so the tensile prestress should be controlled reasonably; the initial defects mainly affect the position of the fold, especially the first position of the fold, and the influence on the number of folds, wavelengths and amplitude, and so on. Obviously.
D. has studied the dynamic characteristics of the structure at different stages of the fold development. The results show that the frequency with the change of the shear displacement angle also shows three typical stages: the initial stage (frequency decrease), the expansion phase (frequency fluctuation) and the stable stage (the slow decline in frequency). In the stable stage, because the structure will be two times flexion, frequency There may be slight fluctuations. The change of mode shapes is more complicated than that of frequency, but the general trend is the increase of vibration modes consistent with the direction of fold.
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU311.3;TU383

【参考文献】