Effect of Material Attenuation on Lamb Wave Propagation in a Solar Cell Array

Abstract

Satellites and other spacecraft rely on solar arrays for power. However, solar arrays are prone to a number of defects which are necessary to detect and repair. For example, bond line defects such as voids in the adhesive may be created during assembly, and disbonds may be caused by a mismatch in the coefficients of thermal expansion and cyclic thermal conditions in space. Lamb waves are a type of ultrasonic guided wave that have been used for nondestructive defect detection in laminates. In this work, they are used to evaluate disbonds at the adhesive interface. One feature of these waves that can be used for detecting and characterizing defects is the peak amplitude. However, material damping may have a significant effect on the amplitude of propagating Lamb waves, especially in polymeric materials. In this study, a single solar cell is modeled using a thermoplastic polymer for the substrate of the array, polycrystalline silicon for the solar cell, and a silicone-based adhesive. The material properties of the substrate, including material damping, are experimentally determined. Then transient structural finite element analyses are conducted on a 2 D model of a solar cell laminate with and without material damping effects included. The results of this study are intended to inform future in-space experiment design, but can also be applied to other layered media containing polymeric materials.