Hysteresis of soft joints embedded with fluid-filled microchannels

Abstract

Many arthropods are known to achieve dynamic stability during rapid locomotion on rough terrains despite the absence of an elaborate nervous system. While muscle viscoelasticity and its inherent friction have been thought to cause this passive absorption of energy, the role of embedded microstructures in muscles and muscle joints has not yet been investigated. Inspired by the soft and flexible hinge joints present in many of these animals, we have carried out displacement-controlled bending of thin elastic slabs embedded with fluid-filled microchannels. During loading, the slab bends uniformly to a critical curvature, beyond which the skin covering the channel buckles with a catastrophic decrease in load. In the reverse cycle, the buckled skin straightens out but at a significantly lower load. In such a loading-unloading cycle, this localized buckling phenomenon results in a dynamic change in the geometry of the joint, which leads to a significant hysteresis in elastic energy. The hysteresis varies nonlinearly with channel diameters and thicknesses of the slab, which is captured by a simple scaling analysis of the phenomenon.

Bioinspired Design of a Hierarchically Structured Adhesive

“…Here, we have amplified this effect by incorporating several planar microchannels and stacking them along the thickness of the adhesive. These internal microstructures alter the local compliance and effective modulus of the adhesive and alter them even dynamically via change in geometry during cyclic loading and unloading . Consequently, indentation results in a non-monotonic load versus displacement plot; Figure b shows that the scaled data do not follow the JKR eq as evident from the inset of the graph which shows the existence of a loop corresponding to adhesion and debonding of the inner walls of the microchannel as shown in the magnified graph 3b.…”

Highly sensitive flexible capacitive pressure sensor with structured elastomeric dielectric layers

“…Hysteresis, however, could result from the sliding of the free end of the micro-pillars on the paper electrode or could be due to an instability observed earlier with the Euler Buckling phenomenon [63]. Ruth et al also noted large hysteresis for a single-sided laminated pressure sensor due to poor adhesion of dielectric microstructure with electrodes [38,64].…”

Microchannel Embedded Elastomeric Layers for Impact Damping

“…In essence, these layers are similar to those that have been used for generating adhesives with embedded microchannels [19,20]. Similar elastic layers have been used also for designing soft joints [21]. In all these examples, the embedded channels play multiple roles, for example, the network of microchannels alters the local modulus of the elastomeric film, so that at the vicinity of the channels the elastic layer becomes more compliant [18].…”