Most thermally triggered reconfigurable mesostructures with shape memory polymers (SMPs) require direct mechanical training at high temperatures. In this work, we suggest a method to generate reconfiguration of mesostructures using preload and reverse stiffness combined with shape memory effects, producing programmable deformations at high temperatures. We analyze the transformation mechanism of the reconfigurable structures, providing a design guideline on the thermomechanical deformation for preloading and geometric conditions of multi-materials. Applying preload to a mechanical assembly, we demonstrate a temperature-triggered shape-change of mesostructures using a reverse stiffness effect at a temperature above its glass transition, followed by recovery with a shape memory effect. Using an analytical model verified by experiments and finite element (FE)-based simulations, we demonstrate the unconventional thermal transformation with recovery for three patterns: circle-tria ngle, circle-square, and circle-hexagon. This work shows that the strain energy conversion by reverse stiffness of two materials, which are designed with prestressing and triggered by temperature, can open a new field of the design of reconfigurable metamaterials.
Jaehyung Ju is an Associate Professor at the University of Michigan - Shanghai Jiao Tong University (UM-SJTU) Joint Institute at Shanghai Jiao Tong University since Fall 2016. He is the recipient of the 2015 Orr Best Paper Award of ASME Journal of Engineering Materials and Technology and 2012 Young Engineer of the Year Award from ASME North Texas Section. His current research interests are in the mechanics and design of mechanical metamaterials with programmable functions. Advanced manufacturing methods, e.g., 3D/4D Printing technologies, have been used for supporting fundamental and applied research. After receiving Ph.D., Dr. Ju had worked in the U.S. academic positions for 11 years including five years at the rank of Assistant Professor at the University of North Texas (UNT), one year at Visiting Assistant Professorship at Texas A&M UniversityKingsville, five years as a postdoctoral scholar at Clemson University and Texas A&M University-College Satiation. He received a Ph.D. degree from the Department of Mechanical Engineering at Texas A&M University-College Station in 2005. He had worked in the CAD/CAM research center at the Korea Institute of Science and Technology (KIST) (1996-2000) as a Research Scientist and Dongyang Technical University (1999-2000) as a Lecturer.