| The fatigue fracture methodology widely used now is built on two-dimensional (2D) theory, but three-dimensional (3D) effect plays an important role in real structures. The research on the strength theory should be developed from the planar to the 3D theory. Therefore, it has very important actual significances to investigate 3D distributions of stresses and fracture parameters at the crack border and stress concentration factors (SCF) at the roots of holes. Following this direction, the 3D I-II mixed mode fracture theory has been successfully used to predict the residual strength of the aircraft component. Meanwhile the 3D stress concentrations at the roots of the hole in the T type structure are also investigated. The following results are achieved:1. The 3D distributions of stresses and fracture parameters at the crack border in the aircraft component are analyzed, the results reveal that the mixed-mode 3D nature of the crack border field scales prevail in the J-dominant zone in the situation of this mixed-mode load, the distribution of the parameter Tz is different from that in the pure I-mode load.2. The residual strength of the aircraft component has been predicted successfully by use of the 3Dâ… -â…¡mixed mode fracture theory; the predicted results have a good direction effect on the experiment processes. When a/B=3.5 and a/B=4.5, the wrong result obtained based on the 2D theory is that the component has been broken, but the result obtained based on the 3D theory reveals that the component is still in a safe state.3. We investigate 3D stress concentration at the roots of the hole in the T type dual-hole structure; it is found that the SCFs distributions along the two sides of the holes are completely different. We find that the plate thickness has pronounced effects on the SCFs especially for the plates with intermediate thickness. The value of Kt on the middle plane of the web is about 25% larger than the results which are obtained on the two free surface of it.
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