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Vibration and wave number characterization in carbon-fiber sandwich composite structures

Sandwich composite structures have highly desirable properties including superior stiffness and strength-to-weight ratios. Such properties arise from combining thin, stiff materials called face sheets with a soft, thick core. Unfortunately these properties give rise to poor acoustic performance, as sandwich structures efficiently radiate noise at low vibrational frequencies. Therefore much consideration has been given to improve acoustic performance with small sacrifices in key mechanical performances, such as bending stiffness and weight. This study focuses on sandwich composite structures with both high noise mitigation and passive structural dampening. Specifically, it is sought to understand how the vibrational responses of carbon-fiber face sheet sandwich composite beams are affected by the core's thickness, as well as its properties. Here, it is shown that the relationship between bending stiffness and coincidence frequency (a metric of acoustic performance) is non-linear. By reducing the core thickness from 10.7mm to 8.4mm, approximately 120% improvement is seen in acoustic performance. Also, the core materials' specific shear modulus is inversely proportional to acoustic performance. Finally, superior damping performance can lead to substantial noise mitigation in low vibrational frequencies. Thus coupling these concepts will provide vastly improved acoustic performance with minimal sacrifices in mechanical performance or weight.