Fatigue of Layered Jamming Materials

There is increasing interest in creating materials by design, like layered jamming materials, that offer enhanced or novel performance, such as the ability to vary properties in situ (i.e., programmable). Many of these materials rely on microstructural characteristics consisting of interfaces, material distributions, and geometric complexity that provide complex stress distributions that result in the desired properties. It has become increasingly apparent that these materials are exhibiting fatigue behavior that has not been observed in conventional materials. In this research effort, we describe efforts to characterize and model fatigue in layered jamming materials, where the elastic-plastic behavior is programmed via vacuum pressure. In order to understand the relationship between the interfacial structure and the subsequent fatigue behavior, we utilized low cycle fatigue experiments conducted on cantilever beams with layers composed of three different types of surfaces: (a) laminated paper, (b) sandpaper, and (c) multi-material polymer layers with 3D printed interfacial features. It was postulated that plastic deformation of surface asperities for laminated paper resulted in a slight increase in the load bearing capacity of the beam, as well as the stiffness. For sandpaper, particle interlocking and decohesion resulted in a substantially higher stiffness but a slightly lower load bearing capacity. Specimens consisting of multi-material polymer layers of rubber and hard plastic with spikes on the surface also exhibited reduction in load bearing capacity and higher stiffness but were dominated by the inherent time-dependent behavior of the layers. An elastic-plastic model we had previously developed for layered jamming materials was successfully applied to these materials. The experimental data and model can potentially be utilized by machine learning techniques to further elucidate on the relationship between the microstructure of the interfaces and the evolution of damage to optimize the macroscopic behavior of these materials by design.