Effect of interlaminar flaw on composite panel behaviour under acoustic loading

A design of airframe structures has to be accompanied by material properties testing. Special focus has to be laid on high frequency fatigue behaviour. The acoustic fatigue test equipment for grazing wave’s incidence was designed based on the FE analyses. Flat composite panels were designed and manufactured using the Hexply 8552/AGP193-PW prepreg with different fiber lay-ups and with simulation of production imperfections or operational damage. Dynamic behaviour of panels was tested using three regimes of acoustic loading: white noise spectrum, engine noise spectrum and discrete harmonic frequencies loading. Rayleigh damping coefficients were evaluated for later use in FE models. Panel health was checked periodically through a power spectral density response on white noise signal. The ultrasonic NDT instruments were used for monitoring of relevant delamination increment. No increments of delamination were detected. The available acoustic power was below the fatigue limit of the tested structure.

Study on the Mechanism of Fatigue Failure at Branch Connections Caused by Shell Mode Vibration

Acoustically induced vibration (AIV) is a vibration of piping systems caused by the acoustic loading generated mainly from pressure reducing devices. Recently, the capacities of the pressure reducing systems have been increased and some of the piping systems which are susceptible to acoustic fatigue, such as in flare and depressuring system. Demands on the development of reasonable design method for AIV is increasing. In this paper, the mechanisms of the fatigue failure of branch connection due to AIV were intensively studied. Firstly, the mechanism of the stress concentration was discussed. branch vibration caused by the shell mode vibration was assessed using several branch connection models, massless rigid model, fixed rigid model, and beam model. Next, the relationship between shell-vibration and stress concentrations is studied and re-organized based on acoustic vibration theories. Finally, the risk of the fatigue failure of the branch connection due to acoustic loading was discussed.