Residual Strength Analysis Of Structures With Multiple Site Damage Based On Crack Tip Opening Angel Criterion

The design and evaluation technology of damage tolerance have been widely used in the structure design of aircraft to make sure the using safety of aircrafts. But the current damage tolerance is designed according to the traditional damage tolerance which takes no account of multiple site damage (MSD). In fact, the structures of aging aircrafts can be often characterized as MSD, which reduce residual strength, critical crack length, the capability of damage tolerance and increase the rate of crack propagation. MSD has badly threatened the structures integrity of aircraft.This thesis consists of two parts. The first part focuses on the experimental analysis of compact tension (C(T)) specimen, middle tension (M(T)) specimen and multiple cracks specimen. The experimental results of C(T) specimen and M(T) specimen have shown that ASTM standard E-2472 is effective to study the crack stable growth behavior of aluminum alloy sheet with 1mm thickness, the crack tip opening angle is nearly a constant value of 6 degree after about 2mm of stable tearing. This value is independent on specimen geometry and initial crack length. It is also found that the constant crack tip opening angle and residual strength obtained from machined and fatigue cracked specimens are nearly the same. The residual strength and the process of fracture of the panel containing single crack and multiple cracks are studied. The experimental results of the panel with MSD have shown that the propagation of multiple cracks undergo stable tearing, linking, unstable tearing and fracture. At the same time, results show that the distribution of multiple cracks effects the residual strength of structures.The second part focuses on the finite element analysis of the panel containing single crack and multiple cracks based on crack tip opening angel criterion. The finite element models which are C(T) specimen, M(T) specimen, MSD specimen, were built using the finite element software ABAQUS. The crack tip opening angel criterion is used to predict the propagation of crack and residual strength. Comparison between the result of experiment and finite element analysis shows that the two results are fitting well. The study results verify that crack tip opening angel criterion can be used to simulate the crack stable tearing process of panels with MSD and predict the residual strength.