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Zhan F.-Y.,Northwestern Polytechnical University | Yang W.,AVIC Chengdu Aircraft Design and Research Institute | Wang S.-N.,Northwestern Polytechnical University | Wang W.,Northwestern Polytechnical University
Gongcheng Lixue/Engineering Mechanics | Year: 2014

It has been the desire of aircraft designers that the structures were devised as ideal as possible, such as lighter weight, higher strength and better durability. The sub-model analysis technology is applied to extract the region of interest from global model for detail analysis. Introducing the damage tolerance constraint conditions, muti-objective optimization for the detail design is completed. The relationships between structure life and geometrical parameters of fuselage opening are discussed. The results reveal that residual strength near the reinforcement structure may rise rather than decrease; crack life is not sensitive to fillet radius of opening; increasing the thickness of skin in a certain range can improve structure life. The solutions of proposed method have better accuracy, which provides reference and guidance for the designing, optimization and maintenance of opening structures.

Guancheng F.,Northwestern Polytechnical University | Guancheng F.,AVIC Chengdu Aircraft Design and Research Institute | Zhenzhou L.,Northwestern Polytechnical University | Wenbin R.,Northwestern Polytechnical University
Journal of Aircraft | Year: 2016

For importance analysis of structural models with correlated inputs, a new method combining support vector machine regression and the single-loop Monte Carlo technique is proposed. In this new combined method, the correlated inputs are transformed to uncorrelated ones by orthogonally independent transformation first, then support vector machine regression is employed to establish the multiple-dimensional regression models involving all inputs, on which the single-loop Monte Carlo is used to obtain the importance measures of the correlated inputs. Support vector machine regression is also used to establish the one-dimensional regression model involving one concerned input. This direct support vector machine regression is proposed as a comparative method. Profiting from the high efficiency of support vector machine regression, the combined and direct methods can get the importance analysis results of the correlated inputs more efficiently than the Monte Carlo simulation. By comparing the results of combined single-loop Monte Carlo technique and those of the direct method, it is found that the former is more efficient and robust than the latter. Several examples illustrate the efficiency and accuracy of the proposed methods. Copyright © 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Ma Y.,Northwestern Polytechnical University | Xia Z.,Northwestern Polytechnical University | Xiong X.,AVIC Chengdu Aircraft Design and Research Institute
Science China: Physics, Mechanics and Astronomy | Year: 2014

Fiber-metal laminates (FMLs) consist of three layers of aluminum alloy 2024-T3 and two layers of glass/epoxy prepreg, and it (it means FMLs) is laminated by Al alloy and fiber alternatively. Fatigue crack growth rates in notched fiber-metal laminates under constant amplitude fatigue loading were studied experimentally and numerically and were compared with them in monolithic 2024-T3 Al alloy plates. It is shown that the fatigue life of FMLs is about 17 times longer than monolithic 2024-T3 Al alloy plate; and crack growth rates in FMLs panels remain constant mostly even when the crack is long, unlike in the monolithic 2024-T3 Al alloy plates. The formula to calculate bridge stress profiles of FMLs was derived based on the fracture theory. A program by Matlab was developed to calculate the distribution of bridge stress in FMLs, and then fatigue growth lives were obtained. Finite element models of FMLs were built and meshed finely to analyze the stress distributions. Both results were compared with the experimental results. They agree well with each other. © 2013 Science China Press and Springer-Verlag Berlin Heidelberg.

Ma Y.,Northwestern Polytechnical University | Hu H.,Northwestern Polytechnical University | Xiong X.,AVIC Chengdu Aircraft Design and Research Institute
Hangkong Xuebao/Acta Aeronautica et Astronautica Sinica | Year: 2014

In order to improve the damage tolerance and anti-impact properties of aircraft structures, fiber metal laminates (FMLs) developed in Europe are successfully applied in commercial aircraft structures. In this paper, drop-weight low-velocity impact tests are performed on FMLs which consist of 2024-T3 aluminium alloy sheets bonded together by glass fiber prepreg. For comparison purposes, similar tests are conducted on monolithic 2024-T3 sheets and F300 quasi-isotropic composite panels. The penetration energy of the FMLs shows respectively about 40% and 6 times higher than that of the 2024-T3 sheets and composite panels; and the back side crack length of the FMLs is 30%-50% shorter than that in the 2024-T3 sheets at the same level of impact energy. Finite element models are developed to simulate the impact response of the FMLs. Ductile and Hashin damage initiation criteria are used to simulate the aluminium and fiber failure mechanisms respectively. The dynamic response of the laminates is analyzed and the damage mode is summarized. The simulation results agree well with the experimental findings.

Zhang S.,Nanjing University of Aeronautics and Astronautics | Shan Y.,Nanjing University of Aeronautics and Astronautics | Zhang J.,Nanjing University of Aeronautics and Astronautics | Zhang Y.,AVIC Chengdu Aircraft Design and Research Institute
Hangkong Xuebao/Acta Aeronautica et Astronautica Sinica | Year: 2012

Based on computational fluid dynamics/infrared radiation (CFD/IR) numerical calculations and validated by experiment, the effect of nozzle pressure ratio and geometry-vector angles of a single expansion ramp nozzle (SERN) on its aerodynamic and infrared radiation characteristics is studied. The results show that when the geometry-vector angle is 0° and the nozzle pressure ratio is low, the aerodynamic characteristic of the nozzle decreases significantly, largely because of over expansion. When the geometry-vector angle is negative, over expansion is more serious and aerodynamic characteristic decreases. With the increase of the absolute value of the geometry-angle, the vector thrust increases, but the thrust coefficient decreases. When the geometry-vector angle is changed from -25° to 25° and the nozzle pressure ratio is changed from 3 to 6, the smallest thrust coefficient is about 0.88 and the biggest thrust coefficient is about 0.98. When the geometry-vector angle is 5°, the infrared radiation of the plume is biggest. When the geometry-vector angle moves away from 5°, the infrared radiation of the plume becomes smaller, but its distribution is not changed. With the variation of the geometry-vector angle, the total infrared radiation of the nozzle presents a different distribution. When the geometry-vector angle is negative, the detecting angle with large infrared radiation is at the underside. When the geometry-vector angle is positive, the upside of the nozzle has large infrared radiation. These are determined by the visible area of the inner wall of the ramp and nozzle lumen.

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