Research On The Fatigue Life Of The Astronautic Structures Under Random Vibration Environment

In astronautic engineering,the structure under the harsh vibration environment is very vulnerable to fatigue damage.As a result,vibration fatigue is a common cause of astronautic structures failure,which could lead to a state of abnormal operation and even cause serious accidents.Since the cumulative process of vibration fatigue damage is irreversible,fatigue damage will not be eliminated once it exists.At the same time,there is no obvious plastic deformation on astronautic structures before their fatigue failure happened,so the fatigue damage on the astronautic structures is not easy to be found.Therefore,once the fatigue damage occurs in astronautic engineering,it will result in serious influence or fatal accident.Thus,it is of great engineering value to predict the vibration fatigue life of astronautic structures.In this paper,taking the astronautic structures as the engineering application background,the random vibration fatigue life prediction methods and random vibration fatigue tests and simulation analysis methods conducted in-depth study.The main works finished in this paper are as follows.(1)The related theories of vibration fatigue are summarized,including the fatigue characteristics of materials,the theories of cumulative fatigue damage,and the characteristics of random vibration are summed up.In addition,several time-domain and frequency-domain methods for stochastic vibration fatigue life prediction of structures are elaborated in this paper.(2)Random vibration fatigue life tests for typical cantilever structure with notches have been designed and finished.Using the time corresponding to the 5% drop in natural frequency as the random vibration fatigue life of the structure,we obtained the life of the specimens under three-axial random vibration environment from these tests results.The possible factors affecting the test results during the test are also discussed.(3)In this paper,a method is proposed to predict the fatigue life of astronautic structures under random vibration,which is based on finite element dynamic simulation and fatigue life estimation theories.Taking the cantilever beam and the typical of astronautic support structure as examples,firstly,finite element modelling,the modal analysis,frequency response analysis and random vibration analysis of the structure were conducted using computer aided design and finite element analysis commercial software MSC.Patran&Nastran respectively,then calculate the random vibration fatigue life of the structure with MATLAB software program.The fatigue life estimation is compared with the experimental values to verify the applicability of the fatigue life prediction method used in this paper.