Impingement of blast or shock waves on structures is characterized by a substantial transient aerodynamic load that develops over the short time associated with the shock reflection time scale. This mutual interaction between the shock wave and the structure can cause significant deformation of the structure and high strain rates within the material resulting in damage. An experimental investigation was carried out to determine the aeroelastic response of thin flat plates of composite materials during face-on impact with planar shock waves. The experiments were performed in a large-scale shock tube research facility, which had a working section of 12 inches in diameter and a length of 80 ft.
Phenolic composite S2-HJ1 plates of 1/8 inch nominal thickness consisting of 12 layers of fibers and epoxy composite S2 plates of 1/8 inch nominal thickness consisting of 10 layers of fibers were tested in the present investigation. Miniature semi-conductor strain-gauges of high frequency response, high speed photography and Digital Image Correlation techniques were employed to measure locally the strain on the exterior side of the plates and high frequency response pressure transducers were used to measure time-dependent wall and total pressure. In order to provide comparison with the response of monolithic material to similar compressive loadings, aluminum and stainless steel plates were also tested under the same conditions. The application of shock loading on the specimen causes significant permanent deformation on the plates which has been measured immediately after the experiment while the specimen is still mounted on the end flange of the shock tube. These experimental data obtained in the present experiments include the measured displacement of the external surface of the plates from their original position in the normal to the plate direction along the radius of the specimen. This displacement is highest at the center of the plate and zero at the location of clamping. The results show that the deformations of the thicker plates are still considerably lower than those obtained in the steel and thinner composite plates although the loading pressure is more than triple in magnitude and the corresponding impulse is about 2.3 times higher. Composite plates were found to suppress several of the modes of the wave patterns while metallic ones demonstrate a rich variety of interacting modes. The frequency content of the strain signals on the surface of composite plates was not always the same with the content of the surface acceleration measured in free vibration experiments.