Take a thin cylindrical shell and twist it; it will buckle immediately. Such unavoidable torsional buckling can lead to systemic failure, for example by disrupting the blood flow through arteries. In this study, we prevent this torsional buckling instability using a combination of auxeticity and orthotropy in cylindrical metamaterial shells with a holey pattern. When the principal axes of the orthotropic meta-shell are relatively aligned with that of the compressive component of the applied stress during twisting, the meta-shell uniformly shrinks in the radial direction as a result of a local buckling instability. This shrinkage coincides with a softening-stiffening transition that leads to ordered stacking of unit cells along the compressive component of the applied stress. These transitions due to local instabilities circumvent the usual torsional instability even under a large twist angle. This study highlights the potential of tailoring anisotropy and programming instabilities in metamaterials, with potential applications in designing mechanical elements for soft robotics, biomechanics or fluidics. As an example of such applications, we demonstrate soft torsional compressor for generating pulsatile flows through a torsion release mechanism.

@en

After decades of coal exploitation during the early 20th century in Limburg, lagging aftereffects at the surface, such as sinkholes, are still experienced today. InSAR time-series have shown to contain information on accelerating surface deformation prior to sinkhole formation. In principle this information may be used as an early warning system. However, the signature for sinkhole deformation are often single point-scatterers which are difficult to identify due to the large surface area of the former mining concessions. Here we exploit georeferenced historical mining maps, an upward drilling data set and building locations to significantly reduce the search space for identifiers of future sinkholes. @en