13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Impact Fatigue Life Prediction of the Wind Tunnel Balance CHEN Ding*, Bu JunHui, SHEN FengJing LIU Peng, ZHANG Yan China Academy of Aerospace Aerodynamics, 100074, Beijing, China * Corresponding author: ringing282@163.com Abstract Impact fatigue damage is the main factor which influenced the life of a wind tunnel balance. It is necessary to predict impact fatigue life of a balance especially in the key points of a balance after static analysis. It is unpractical to implement the impact fatigue experiment in the laboratory while wind tunnel balance is a special transducer which would not be manufactured in batches. Generally, balance designers didn’t do this analysis for its special use. In fact, accidents of this sort which is in the testing are happening with increasing frequency. This paper provided a method to predict impact fatigue life of a balance which based on the finite element analysis. We used finite element analysis tools to modeling the wind tunnel balance, and then we meshed the whole model as fine as possible. After that, stress of the wind tunnel balance under static loading was figured out, as well as the key points of the balance. The fatigue analysis tools were used to estimate the stress of the balance which was bearing the impact loading. These analysis results would much valuable to the wind tunnel testing. Keywords wind tunnel balance, fatigue damage, finite element analysis 1. Introduction Wind tunnel balance is used in the wind tunnel widely by the enlargement of the wind tunnel testing, thus the performance of the balance is more attractive to the researchers. These researchers focused on the failure and accident of the wind tunnel balance, because they doubt that the fatigue of the balance is the main factor of these accidents. But what is the fatigue? Maybe this is the first thing which the wind tunnel balance researchers want to know eagerly. Here quote a definition of ASTM E206-72: The process of progressive localized permanent structural change occurring in a material subjected to conditions which produce fluctuating stresses and strains at some point or points and which may culminate in crack or complete fracture after a sufficient number of fluctuations. The actual mechanization of the material fatigue and its scientific describe are not reported at present. Analysis method of fatigue life prediction is the main aspect of fatigue, and this content was concluded throughout of the history of fatigue. For the cost of the fatigue testing is so large that most researchers tend to using finite element analysis to acquire the data of the material which they concerned. Finite element analysis is the most important method for the researcher to develop a new balance for the wind tunnel balance is special research equipment which is unpractical to proceed the fatigue testing. The purpose of a wind tunnel balance is to measure the aerodynamic forces and moments, which load a model during wind tunnel tests. The balance measures the aerodynamic forces and moments by the wheatstone bridge which consist of strain gauges adhere to the sensitive elements. The sensitive elements suffered pull、torsion、torsion and bend，and even the combination of them. A slot partition a balance into two parts, the axial force elements combined these as a parallelogram. The forces and moments will transfer from model to the balance. The balance used in the airplane was show in figure1.
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