Modal Characteristics of Carbon Fiber Reinforced Composite Structure at High Temperature

Flight vehicles that fly at high Mach speeds will be exposed to a severe aerodynamic heating problem, which leads to high surface temperatures and large temperature gradients. Thermal load will induce thermal stress, thermal deformation, and even thermal buckling. Therefore, the dynamic stiffness and the modal characteristics will be affected. In this paper, several tests are carried out for a plain woven carbon-fiber-reinforced silicon carbide (C/SiC) composite plate under elevated temperature. The plate is heated by a quartz-lamp radiation heating system. A three-dimensional digital image correlation system is first employed to obtain the relationship between displacements and temperature to get the critical buckled temperature. Then, the thermal modal tests are performed by a laser scanning vibrometer to investigate the effect of thermal loads on modal parameters: especially the effect of the critical buckled temperature. A specific fixture with water cooled is designed in order to avoid the influence of the uncertainty of the boundary condition since the modal parameters are very sensitive to the boundary condition. Finally, the numerical simulation process of the high-temperature modal tests for the buckled plate is presented to investigate the contributions from temperature-dependent material properties and thermal stresses. As the temperature increases, the modal frequencies reduce. After the critical buckled temperature, the modal frequencies increase. A parametric study is further performed using the presented numerical model to investigate the thermal modal characteristics of C/SiC composite plates with various thickness and boundary conditions.