| Turbofan engine intermediate casing is an important load-bearing component to withstand the aerodynamic loads and the complex maneuvering loads from aircraft. Intermediate casing of the advanced engine is made of by casting, and in the manufacturing process it is unavoidable to introduce a variety of casting defects. To ensure the safety and durability, it is necessary to conduct damage tolerance design and analysis. One of the key technology is fatigue crack growth analysis under multiaxial loading.The numerical simulation methods of mixed mode center through crack in plate under constant amplitude fatigue loads are studied. A numerical simulation process and method based on the commercial finite element code is proposed. The calculation methods of stress intensity factor and the selection of crack growth step are studied and evaluated. The result shows that using singular element method, a better accuracy can be abtained with coarse mesh and the ratio of singular element feature length to crack size should be controlled at 1/10 or less. It also shows that for the mixed mode crack, when crack propagation step is between 100 and 500, it has no significant effect on numerical simulated crack path.The crack growth process of a rectangular plate with a center crack of 2024-T3 aluminum alloy and a Compact-Tension specimen of 6082-T6 aluminum alloy is simulated by the method metioned above. The results show that the difference between the crack open angle predicted by the maximum tangential stress criterion and the minimum strain energy density criterion is little. There has no evident difference between the crack path simulated by the crack growth models evaluated, but has some distinction with the observed crack path in fatigue test. The crack growth life predicted by effective stress intensity factor crack growth rate model is less than by the strain energy density factor crack growth rate model. |
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