Hygrothermal behavior of electro-active paper actuator

Mechanical properties of the electro-active paper (EAPap) actuator were tested to investigate its hygrothermal behavior. Tensile creep behavior was studied with constant load at 30–70% relative humidity ranges and 25–40°C temperature. Creep deformation showed typical trend of abrupt strain increase in a short period followed by steady increase of strain, which resulted from the breakdown of cellulose microfibrils. Dependence on the material orientation of EAPap was observed in the creep tests. As changing the orientation of EAPap samples, the creep resistances were varied. Creep strains and creep strain rates were increased as increasing the relative humidity level at 25°C. However, at the elevated temperature of 40°C, the creep strain rate at secondary creep was not significantly raised under increased relative humidity level from 30% to 50%. The hygrothermal effect by increasing the relative humidity level and temperature on the creep rate was reduced due to the saturated moisture at a higher temperature even with lower humidity level. The activation energy levels for creep were around 607–658 kJ/mol for 30% relative humidity level and 623–671 kJ/mol for 50% relative humidity level depending on the material orientation. Understanding of hygrothermal effect in conjunction with the humidity and temperature provides useful information for the potential nano-bio applications of the EAPap actuator. This paper was recommended for publication in revised form by Associate Editor Chongdu Cho Heung Soo Kim received his B.S. and M.S. degrees in the Department of Aerospace Engineering from Inha University, Korea in 1997 and 1999, respectively. He got his Ph. D degree in the Department of Mechanical and Aerospace Engineering from Arizona State University in 2003. He is now working as an assistant professor in the School of Mechanical and Automotive Engineering, Catholic University of Daegu. His main research interests are in biomimetic actuators and sensors, structural health monitoring, smart materials and structures as applied to aerospace structures and vehicles. Chulho Yang received his B.S. and M.S. degree in Mechanical Engineering from Inha University in 1991 and 1993, respectively. He also obtained M.S. and Ph. D degree in Mechanical Engineering from University of Florida in 1995, and 1997, respectively. In March 2003, he joined the School of Mechanical Engineering at Andong National University, Korea, where he is now an Associate Professor. His main research interests are mechanical behavior of materials including smart materials both experimentally and computationally. Jaehwan Kim received his B.S. degree in Mechanical Engineering from Inha University, in 1985. He received his M.S. degree from KAIST in 1987 and his Ph.D. degree from The Pennsylvania State University in 1995. Dr. Kim is currently a Professor of Dept. of Mechanical Engineering at Inha University, Inchoen, Korea. He serves as an Associate Editor of Smart Materials and Structures. He is the director of Creative Research Center for EAPap Actuator supported by KOSEF. Dr. Kim’s research interests are smart materials such as piezoelectric materials, electro-active polymers and their applications including sensors, actuators, motors and MEMS devices.