Constitutive Model And Vibration Analysis Of Ceramic Matrix Composites

Ceramic Matrix Composites(CMCs)show a good prospect in the field of aerospace,because of its excellent high temperature performance.The CMCs used in engineering usually consist of complex preforms and burden dynamic loads.As a result,the composites present very different damage modes and behavior.If not designed properly,the CMCs structures may be damaged due to resonance.To avoid such situation,the present study will focus on the dynamic properties of the CMCs.The mechanical testing of 2D needled C/SiC composites has been performed.The properties of the composites under loading-unloading have been achieved.A stiffness degradation behavior was found in 2D needled C/SiC composites,and the effects of stress level was studied.Besides,the frequency-sweep tests of a 2D needle C/SiC composites beam under base excitation was conducted.A natural frequency shifting behavior was found and the effect of the load level on the natural frequency,amplitude and damping was discussed.A polynomial fitting method was adopted to describe the stress-strain hysteresis loops and then an empir ical constitutive model was developed.Besides,a multi-scale model was adopted to describe the constitutive model of the composites.The representative volume element(RVE)of the composite was chosen through X-ray CT technology.The property of the basic component of the RVE,the unidirectional layer,was described by the shear lag model.Accordingly,the stress-strain curve of the 2D needled C/SiC composites was simulated using finite element method.Employing the empirical constitutive model and the central difference method,the displacement response of the composites beam under vibration load was calculated in the time domain,and the frequency-amplitude curves were obtained.Through replacing the vibration mode with the static deflection,the damage state of the composites beam was simulated with the multi-scale model.With the stiffness degradation,the modal model was analyzed in the frequency domain and the natural frequency was obtained.