The Woodruff School

SUMMARY

Flexible electronics is increasingly used in wearable devices, displays, solar cells, and other applications. Printed flexible electronics, an important part of 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. Therefore, it is essential to characterize and understand the electromechanical behavior of flexible electronic components under various mechanical deformations. This work aims to study the mechanical and electrical behavior of printed silver conductors under a wide range of bending modalities, using conductors printed on polyimide (PI), polyethylene terephthalate (PET), and thermoplastic polyurethane (TPU). These samples have been subjected to mandrel bend test, varying-gap adaptive flexure test, as well as reciprocating adaptive flexure test. In all the tests, the resistance of the printed conductor was monitored continuously by a 4-wire method. In the mandrel bend test, the strain is uniform so that the relationship between the resistance and the bending strain can be obtained. These results can be further used to understand the resistance change of the printed conductor in the varying-gap and reciprocating adaptive curvature flexure tests, where the strain distribution along conductor length is non-uniform unlike mandrel bend test or stretch tests. By performing these three bend tests under cyclic conditions, the resistance change with loading cycles has been investigated and related to the microstructure changes through SEM imaging. Besides, analytical formulations of the various bending configurations and finite-element simulations have been performed to get a comprehensive understanding of the stress and strain distribution in the conductor and to determine damage accumulation in the printed conductors. With adaptive curvature and mandrel bend tests, predictive models for damage evolution with strain amplitude have also been explored. BlueJeans link: https://bluejeans.com/567011348/2837?src=calendarLink

SUBJECT:	Ph.D. Dissertation Defense

BY:	Rui Chen

TIME:	Tuesday, November 17, 2020, 12:00 p.m.

PLACE:	BlueJeans, Online

TITLE:	Damage Evolution and Failure Mechanism in Flexible, Printed Conductors under Monotonic and Cyclic Bending

COMMITTEE:	Dr. Suresh K. Sitaraman, Chair (ME) Dr. Karl I. Jacob (ME) Dr. Yuhang Hu (ME) Dr. Ben Wang (ISYE) Dr. Emmanouil M Tentzeris (ECE)

SUMMARY Flexible electronics is increasingly used in wearable devices, displays, solar cells, and other applications. Printed flexible electronics, an important part of 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. Therefore, it is essential to characterize and understand the electromechanical behavior of flexible electronic components under various mechanical deformations. This work aims to study the mechanical and electrical behavior of printed silver conductors under a wide range of bending modalities, using conductors printed on polyimide (PI), polyethylene terephthalate (PET), and thermoplastic polyurethane (TPU). These samples have been subjected to mandrel bend test, varying-gap adaptive flexure test, as well as reciprocating adaptive flexure test. In all the tests, the resistance of the printed conductor was monitored continuously by a 4-wire method. In the mandrel bend test, the strain is uniform so that the relationship between the resistance and the bending strain can be obtained. These results can be further used to understand the resistance change of the printed conductor in the varying-gap and reciprocating adaptive curvature flexure tests, where the strain distribution along conductor length is non-uniform unlike mandrel bend test or stretch tests. By performing these three bend tests under cyclic conditions, the resistance change with loading cycles has been investigated and related to the microstructure changes through SEM imaging. Besides, analytical formulations of the various bending configurations and finite-element simulations have been performed to get a comprehensive understanding of the stress and strain distribution in the conductor and to determine damage accumulation in the printed conductors. With adaptive curvature and mandrel bend tests, predictive models for damage evolution with strain amplitude have also been explored. BlueJeans link: https://bluejeans.com/567011348/2837?src=calendarLink