Three-dimensional Stress Concentrations At Holes And Fractures For Aircraft Contectors

Many widely used mechanical equipments in engineering such as aircrafts and aerospace crafts usually consist of complex components. During the service period, the damages of the components usually occur due to loads and inherent faults of the materials. The current widely used fatigue fracture methodology is mainly based on the traditional two-dimensional (2D) fracture theory. Furthermore, the strong three-dimensional (3D) effects often occur when they are appilied to complex structures. Therefore, researches on the three-dimensional damage of the complex mechanical structures have significant meanings in theory and applications. In the present thesis, we focused on the three-dimensional fracture of thin plates with cracks and the stress concentration of finite thickness plate with a pin hole. The main contents are as following:1.Under remote uniform tensile load, anisotropic thin plates with single edge through straight crack are investigated and analyzed using 3D finite element method. The relationship between the stress intensity factors and relative crack lengths is obtained.The influences of crack length and Poisson's ratio for out-of-plane constraint factor at the crack tip are detailedly studied. For convenience of engineering applications, the empirical formula is obtained.2.Through the simplification of the problem of a double-lap mechanical joint of finite thickness isotropic plates with a pin-loaded hole under tensile load at both ends, we study it as a basis problem, that is, tension is applied on one end of the finite thickness plate with a hole, and equivalent even pressure with different angles is applied on the inside of the hole to balance the tension. The relationships between the stress concentration at the hole edge and the plate thicknesses and the loading angles are investigated by use of linear elastic superposition principle and the finite elements method.3.We also study another problem of a finite thickness plate with a pin-loaded hole. In this case, tension is applied on one end of the plate, and equivalent sine compressive stress with different angles is applied on the inside of the pin-loaded hole to balance the tension. The influences of the stress concentration by the different loading angles and the plate thicknesses are discussed. It is found that the loading angles and variation of plate thicknesses obviously affect the 3D stress concentration coefficients. Therefore, we cannot obtain reasonable results using simple planar solution or surface stress concentration coefficient instead of 3D maximum stress concentration coefficient.