Effects of interply damping layers on the dynamic characteristics ofcomposite plates

Abstract

Integrated damping mechanics for composite plates with constrained interlaminar layers of polymer damping materials are developed. Discrete layer damping mechanics are presented for composite laminates with damping layers, in connection with a semianalytical method for predicting the modal damping in simply supported specialty composite plates. Correlations between predicted and measured response in graphite/epox y plates illustrate the accuracy of the method. Additional application cases for graphite/epoxy plates of various laminations demonstrate the potential for higher damping than geometrically equivalent aluminum plates. The effects of aspect ratio, damping layer thickness, and fiber volume ratio on static and dynamic characteristics of the composite plate are also investigated. AMPING is a significant dynamic parameter for vibration and sound control, dynamic stability, positioning accu- racy, fatigue endurance, and impact resistance. Many current structural applications (e.g., large space structures, engine blades, and high-speed machinery) require light weight and high dynamic performance. Therefore, candidate sources of passive damping should add minimal parasitic weight and be compatible with the structural configuration. Two potential damping sources satisfying the previous re- quirements are the constrained damping layer approach and the damping capacity of composites. Constrained damping layers in isotropic metallic structures have been widely applied and investigated.1 They provide high damping, but tend to increase the structural weight and offer limited means for damping tailoring. The inherent damping capacity of compos- ite materials also seems promising. Although the damping of composite structures is not very high, it is significantly higher than that for most common metallic structures. Moreover, composites are the materials of preference in many cases, since they readily provide high specific stiffness and strength. More importantly, research on the damping mechanics of composite laminates2'4 and structures5'6 has shown that composite damp- ing is anisotropic, highly tailorable, and depends on an array of micromechanic al, laminate, and structural parameters. It has been further demonstrated that optimal tailoring may significantly improve the damped dynamic performance of composite structures.7 It seems likely that the combination of both approaches (i.e., composite structures with interlaminar damping layers) will offer the advantages of high damping, damping tailoring, good mechanical properties, and low weight addition. In addi- tion, the interlaminar damping concept is highly compatible with the laminated configuration of composite structures and their fabrication techniques. In contrast to isotropic materials, the variations in anisotropy and elastic properties of each