Actuation-softening in kagome lattice structures

Abstract

The two-dimensional kagome lattice has been shown to be a promising basis for active shape-changing structures, having both low actuation resistance and high passive stiffness. Linear actuators replace some members of the truss: activation of the actuators results in a global macroscopic shape change. The linear behaviour of the structure, and in particular the high passive stiffness, depends crucially on the straight bars running across the structure; but this straightness is destroyed when bars are actuated. The current paper investigates this behaviour by imposing large actuations to create geometrically non-linearity. A column of actuators is introduced into a kagome lattice, so that for every actuator, the actuator directly above and below is also activated; the horizontal stiffness of the system is then measured. Numerical results show that when the actuators are extended, there is a sudden drop in passive stiffness at a ‘critical’ actuation strain. This critical actuation strain depends on the stockiness of the bars of the lattice, and the stiffness of the actuator itself. For lattices with contracting actuators, the stiffness degradation is gradual, and less severe.