Characterization of variable stiffness joints for adaptive structures

This paper presents a new strategy to control the structure dynamic response via a shift of the natural frequencies obtained through using variable stiffness joints. The joints are made of shape memory pol-ymers and are fabricated through 3D printing. Stiffness variation is activated through resistive heating which causes a phase change from a glassy to a rubbery state in order to switch the joint between a ‘locked’ (e.g. a moment connection) and a ‘released’ (e.g. pin) state. This work comprises an experimental and a numerical part: 1) dynamic mechanical thermal analysis (DMTA) has been carried out to characterize the viscoelastic behavior of a 3D printed SMP specimen; 2) the dynamic response of a 2-floor planar frame equipped with four variable stiffness SMP joints is simulated through transient analysis. Numerical results show that through joint stiffness control, the fundamental frequency shifts up to 19% causing a drastic reduction of the dynamic re-sponse under resonance loading. A comparison between variable stiffness joints with viscoelastic and only-elastic behavior shows that viscoelasticity increases mechanical damping up to 4.7 times during the transition phase.