Abstract
Solar arrays provide electricity to spacecraft by converting energy from the sun. Generally, solar arrays are made by adhering multiple solar cells to a substrate, usually with silicone based adhesives. They may be prone to disbond failures at the cell interface due to mismatch of the coefficients of thermal expansion. Manufacturing errors like voids in the adhesive layer can also occur. If disbonds are not detected and repaired, the electrical interconnects can fail due to cyclic thermal loads in space. This is significant because the failure of even one interconnect can cause power loss to a number of cells. This paper aims to evaluate the feasibility and sensitivity of inspecting bonded joints in solar arrays in space. One potential nondestructive evaluation technique relies on Lamb waves. These waves have been used for disbond detection in layered media. In this work, this methodology is extended to detecting disbonds between layers of different materials and sizes as in the case of a solar cell bonded to a larger substrate. Transient structural finite element analyses are conducted using Abaqus. For simplicity, a 2D representation is modeled of an isolated silicon solar cell bonded to a larger polymer substrate panel. Disbonds of varying size and location are studied and compared to a pristine case with no disbond between the cell and substrate. Several damage indices are defined and evaluated for effectiveness in indicating specific defect characteristics. Using these damage indices, almost all of the tested disbond cases are shown to be fully characterizable according to size and location, including disbonds as small as 1 mm. The results of this study could be applicable beyond the scope of this work to any layered medium with materials of highly dissimilar stiffness.
