薄弱环节有望解决复合材料结构耐撞性设计

复合材料具有比强度高、比刚度大、比吸能能力强及可设计性等优点,目前已在国防工业和民用工业,特别是航空航天领域得到了越来越多的应用。近年来,由于复合材料结构耐撞性的重要性和复杂性,所以,复合材料结构耐撞性是工程力学领域的一个研究的热点。本文采用试验和数值模拟相结合的方法,对典型复合材料结构元件的耐撞性进行了系统的研究,还对影响复合材料结构耐撞性的关键问题——薄弱环节进行了比较深入的探讨。论文首先介绍典型复合材料结构元件与结构件(波纹梁、圆柱壳、“T”字形元件、“十”字形元件、“L”字形元件和波纹梁盒段)的准静态轴向压溃试验,给出了其载荷-位移曲线和典型的破坏模式和吸能机理。试验结果表明,设计合理的复合材料结构元件与结构的确具有较好的比吸能能力。建立了运用大型商用有限元软件(MSC/DYTRAN)模拟复合材料结构耐撞性的策略与方法,包括采用等效材料模型和有效的薄弱环节处理的方法。然后,对各种复合材料结构元件的轴向压缩吸能能力进行了数值模拟。数值模拟的结果与试验结果吻合得比较好说明了所建立的模拟复合材料结构耐撞性的策略与方法是可行的。另外,还采用所建立的数值模拟的方法进一步研究了不同薄弱环节设置对复合材料波纹梁元件耐撞性的影响。提出了基于形状记忆合金(SMA)丝可控薄弱环节的概念并采用试验进行了验证。将有预变形的SMA丝埋入或者缠绕于复合材料圆柱壳结构中形成一种新的薄弱环节。温度升到相变温度后,有预变形的形状记忆合金丝将回复到原先的长度,造成结构的局部变形或者引起局部损伤,从而形成可控薄弱环节。该薄弱环节有望解决复合材料结构耐撞性设计中静强度(刚度)与耐撞性之间的矛盾问题。自制了一些试验件并对其进行了试验,初步试验结果表明的确可以形成可控薄弱环节,并可以改善复合材料结构的耐撞性能。最后对全文的研究成果进行了总结,并展望了今后需要进一步开展的研究工作。
逆变焊机
Advanced composite materials are widely used in the industry of national defense and civil, especially in the areas of aeronautics and astronautics, due to their superior property of high specific strength and stiffness, high specific energy absorption, and designable capability. The crashworthiness of composite structures has become a hot research topic in recent years because of its importance and complicated nature. In this thesis, the crashworthiness of typical composite components and structure is explored systemically by using numerical simulations together with the experimental research. Special attention has also been paid on the trigger mechanism, an important issue affecting the energy absorption capability of composite structures.The energy-absorbing capability of typical composite structural elements, such as waved beam, cylindrical shell,“T”shape element,“十”shape element,“L”shape element and corrugated board boxes, under quasi-static axial loading is experimentally investigated first. The load-displacements and typical damage patterns and mechanisms of composite structural elements are obtained. Experimental results demonstrate that well-designed composite structural elements do have a good specific energy-absorption capability.A FEM-based numerical strategy and means is proposed to simulate the crashworthiness of composite structures by using the MSC/DYTRAN FE software, including adopting the equivalent material models and using a simple way to model the trigger mechanism. The energy absorption ability of various composite structural elements under axial compressive loads is then simulated. Numerical results are compared well with experimental results, thus the established FEM-based numerical strategy and means is verified. In addition, the effect of different settings of trigger mechanism on the crashworthiness of waved beams is numerically investigated.The SMA (Shape Memory Alloy) -based controllable trigger mechanism is proposed and experimentally verified. Pre-strained SMA wires are embedded into or winded up onto the composite cylinders to form a new kind of trigger mechanism. The pre-strained SMA wire will shrink back to its original length when it is heated to the transformation temperature, consequently will cause the local deformation, thus a controllable trigger mechanism is formed. This controllable trigger mechanism could solve the contradicted requirements between the structural strength (stiffness) and the crashworthiness. Specimens have been made in the Lab and tested. Preliminary test results show that a controllable trigger mechanism does formed and could improve the crashworthiness of composite structures.The dissertation is ended with the summary remarks and the future research topics in this field.