【作者】 孟令兵；

【导师】 陈普会；

【作者基本信息】 南京航空航天大学 ， 飞行器设计， 2009， 硕士

【摘要】 分层是是复合材料结构失效的主要原因之一。为了更合理有效的利用复合材料,有必要对复合材料分层机理进行研究分析。本文提出了一种基于虚拟裂纹闭合技术的界面元模型,用以模拟含初始损伤的复合材料结构的分层破坏问题。本文主要内容如下:(1)介绍了虚拟裂纹闭合技术的原理、发展历史和应用。(2)提出了一种基于虚拟裂纹闭合技术的界面元模型。该界面元被嵌入在模型分层的潜在路径上,用来计算结构的能量释放率,结合幂指数破坏准则,模拟复合材料的分层扩展。在实际模型中,由于裂尖前后单元长度的不同,会带来一定的分析误差。本文对其进行了适当的修正,以降低网格粗细变化所带来的不利影响。(3)介绍了ABAQUS中UEL模块的界面、接口和开发用户自定义单元的流程,以及调用多个子程序的方法。(4)引入双悬臂梁模型(DCB)、端边切口模型(ENF)和混合模式弯曲模型(MMB)来检验该界面元方法的可靠性。本文分别推导了DCB、ENF、MMB模型能量释放率和载荷位移关系的解析解。在有限元分析中,用界面元来模拟这三种模型的界面层。模拟结果与解析解吻合较好,证实了该方法模拟I型、II型和I、II混合型分层破坏的有效性和可靠性。(5)在上述研究的基础上,本文最后将该方法引入工程实际问题,分别对三个含有不同初始损伤的复合材料T型接头的界面拉脱分层破坏进行数值模拟,取得了令人满意的结果。更多还原

【Abstract】 One of the most common failure modes for composite structures is delamination. In order to utilizing the composite laminate more effectively, the delamination mechanics is necessary to be studied. In this thesis, an interface element model based on the virtual crack closure technique (VCCT) is introduced to study 2D delamination growth problem in composite. The main content of this thesis is summarized as follows:(1) The approach, history and applications of the virtual crack closure technique is introduced.(2) An interface element based on the virtual crack closure technique is defined in this thesis. The mechanics of the interface element is interpreted first. The interface element are embedded along the potential crack path in advance to calculate the strain energy release rate and simulate the delamination growth of composite laminates in conjunction with the power law fracture criteria. In practical models, the different length of the elements at the crack tip will induce inaccuracy in numerical modeling. Therefore, a necessary correction has been considered as a strategy to minimize the negative effect of change in mesh density on numerical results.(3) The interface keywords, strategy and regulation of the user subroutine(UEL) in ABAQUS are presented. Besides, the method how to invoke user-defined elements is also mentioned in this thesis.(4) The DCB, ENF and MMB models are taken in to validate this approach. The analytical solutions are deduced before the numerical simulation. Interface elements are employed to simulate the interface in these models. The results of the FE simulation agree well with analytical solutions. It confirms that the approach is reliable and feasible for modeling the delamination growth in composite laminates.(5) Finally, the approach is applied in engineering problems. Three composite T-joints with different flaws are numerically simulated with the interface element. An excellent agreement is found between the numerical results and the experimental data.更多还原