Study On Three-dimensional Damage Tolerance Of Mixed-mode Surface Crack In Some Aircraft Component

Structures and components containing initial surface cracks are used widely under mixed-mode loading conditions in aircraft and aerospace engineering. Stress field calculation near the crack border and analysis in damage tolerance are closely related to structure's safety and life designing in aircraft. At present, damage tolerance evaluations are still based on two-dimensional fracture theory in engineering. However, there are evident three-dimensional effects in real structures due to the influence from complex structure and loading conditions. In this thesis, a series of studies are carried out in the inclined semi-elliptic surface crack in elastic plate, in three-dimensional residual strength of the structure, and in predicting propagation life of the cracked structure. The main work and results are as following:1. For the inclined semi-elliptic surface crack in elastic plate, distributions of mixed-mode stress intensity factors are presented along the whole surface crack front in this paper, and the effects are considered carefully on stress intensity factors from the aspect ratio a/c, the crack length/plate thickness ratio a/t, the inclination angle of crack planeβandυ. Along the whole mixed-mode crack front, mode-I stress intensity factors are chiefly affected by a/t, and changes in mode-II stress intensity factors are mainly affected by a/c, and mode-III stress intensity factors are seldom affected by the parameter a/c and a/t. Whenβ≥45°, three-dimensional constraint factor TZ become more serious and affected by a/c, thus three effects should be stressed, and mode-II and mode-III stress intensity factors should not be neglected.2. Basing on three-dimensional elastic mechanics and fracture theory, we gave the prediction results of three-dimensional residual strength of complex structure containing surface crack by finite element method. Compared with the prediction results based on two-dimensional plane-strain fracture theory, three-dimensional fracture theory possesses more potential application prospect in engineering.3. For the actual cracked structure, fatigue crack propagation process was simulated under complex loading conditions. The simulation results can provide reference for damage tolerance designing and virtual experiment study in aircraft engineering.