Anti-Fatigue Analysis And Detail Optimization For Undercarriage Bay Of Aircraft

The performances of an aircraft are directly involved by its weight, at the same time the fatigue life has also become a significant objective in structural optimization. These are important problems needed to be settled, such as extending its application range, enhancing its efficiency and quality, and making the optimization depending on the variable and target numbers as little as possible. Fatigue reliability analyses based on DFR method and anti-fatigue optimization of detail structures are presented in this paper.Firstly, based on original research a new method to calculate the nominal stress is raised. In order to get the true nominal stress, the loads of the nodes around the pin node are transformed into the local coordinate whose X-direction is the direction of pin-load. Then coupling VC++ with MATLAB, setting an interface with NASTRAN, a fatigue reliability calculating software, which termed FEM-DFR by author, is given. It can automatically search the load distribution around the pin, calculate the nominal stress, and analyze the fatigue reliability.Secondly, the nose undercarriage bay is analyzed, including selecting analysis load spectrum, establishing an FEM model to analyze general stress, though the result selecting critical dangerous detail and analyzing it, at last, solving fatigue reliability at FEM-DFR. According to the result, the anti-fatigue design of undercarriage bay of an aircraft is appropriate, but tending to conservative. Thirdly, a platform named AFOP is settled, integrating PATRAN/NASTRAN, FEM-DFR and iSIGHT. There are 9 data interfaces to transform the data among the software, which improve the optimization efficient, cut down the repeated work, to make the software efficient and convenient.At last, a multi-objective optimization including structural mass, maximum Von Mises stress and fatigue life is presented for the detail bracket of actuator cylinder, including its sensitivity. The optimization result indicates that in the situation that Von Mises stress keeps a constant, the optimum of the bracket reinforced by a plate makes the mass reduce 20.17%, while the one without the plate can reduce the mass 22.2%.