Analytical and experimental studies of composite isogrid structures with integral passive damping

Composite isogrid structure are currently in use in a number of aerospace applications where the control of structural vibration response is an important design consideration. In this paper, a recent investigation of the modal vibration characteristics of composite isogrid structures with embedded viscoelastic damping layers will be summarized. Analysis was done by means of the finite-element-based modal strain energy method, while experiments were done by using an impulse-frequency response technique. Composite isogrid test panels were fabricated by a fast and inexpensive thermoplastic stamping process using co-mingled glass/polypropylene. The viscoelastic layer damping materials were embedded at the interface between the ribs and the skin, where the shear deformations are greatest in order to significantly improve the damping properties of the structures. Good agreement between measured and predicted modal frequencies and damping factors was found in the cases where degradation of the damping layer during the thermoplastic stamping process was avoided by using a secondary bonding process. It was also found that the required amount of damping material could be reduced significantly if it is optimally placed.