Development of a shape memory polymer fastening system

Abstract

Traditional fastening systems exhibit various limitations that a next-generation shape memory polymer (SMP) system can overcome. Bolts and screws provide high-strength attachment but require permanent modification to the system and are typically visible, depending on the configuration. Adhesive bonding can provide high-strength attachment and low visibility, but it is irreversible. Hook and loop fasteners offer reversibility, but the fastened strength and the removal force are similar, limiting the applications. The unique properties of SMP enable a fastening system that offers advantages not currently available in any one fastening system, including reversibility, low visibility, and high-strength attachment. Cornerstone Research Group (CRG) designed a fastener system that consists of an array of SMP heads and stems that interlock. The high modulus of the SMP at room temperature provides rigid attachment, keeping the system interlocked. When activated above the glass transition temperature (T_g), the heads and stems become soft and flexible, reducing the force required during attachment and detachment of the system. The shape memory property of the SMP ensures all heads and stems return to their original position to allow proper alignment. The developed system provides shear and tensile strength in excess of 300 psi with tensile detachment requiring only 2 psi. The material selection, design, testing, and optimization of the SMP fastening system are discussed.