SUMMARY

Flexible electronics has attracted significant amount of interest in both academia and industry. They have already been widely used in wearable devices, flexible displays, solar cells, and other areas. However, printed flexible electronics is still in its early stages of development and growth, and the performance of printed flexible electronics under various deformation conditions is not fully understood. Such deformations include both monotonic and fatigue stretching, bending, twisting, and combined deformations under practical operating conditions. Thus, compared to traditional “rigid” electronics, flexible electronics undergoes much larger deformations. Therefore, it is important to identify the electromechanical behavior of flexible electronic components under these mechanical deformations.
The objective of this research is to study and understand mechanical and electrical behavior of a printed silver conductor under various bending conditions. This work will employ conductors printed on polyimide, polyethylene terephthalate (PET), and thermoplastic polyurethane (TPU), and subject them to both adaptive flexure test with a varying radius of curvature as well as mandrel bending test with a constant radius of curvature. In the adaptive curvature flexure test, the printed conductor on a flexible substrate is bent between two rigid parallel plates so that the bending strain will be generated through the conductor and thus cause resistance change. Both tensile and compressive strains will be created in the printed conductor. During such testing, the resistance of the conductor is continuously measured by a four-wire method. Both the single load-unload step test and the cyclic tests will be performed, and the damage evolution in the conductors will be monitored through in-situ electrical resistance as well as SEM imaging. In addition, theoretical analysis and finite-element simulations are performed to get a comprehensive understanding of the stress and strain distribution in the conductor, and correlate such distribution to the damage evolution. Similarly, the mandrel bend test is also employed to get the relationship between the resistivity and bending strain, and mandrels of various diameters will be used for this test. Both compressive and tensile bending as well as cyclic bending will be employed. With adaptive curvature and mandrel bend tests, predictive models for damage evolution with strain amplitude will be explored.