SearcharxivSearch

arXiv subjects

David Dykstra

Publications and source records attributed to David Dykstra.

2 recordsLinked to original sources

Leveraging yield buckling to achieve ideal shock absorbers

The ideal shock absorber combines high stiffness with high energy absorption whilst retaining structural integrity after impact and is scalable for industrial production. So far no structure meets all of these criteria. Here, we introduce a special occurrence of plastic buckling as a design concept for mechanical metamaterials that combine all the elements required of an ideal shock absorber. By striking a balance between plastic deformation and buckling, which we term yield buckling, these metamaterials exhibit sequential, maximally dissipative collapse combined with high strength and the preservation of structural integrity. Unlike existing structures, this design paradigm is applicable to all elastoplastic materials at any length scale and hence will lead to a new generation of shock absorbers with enhanced safety and sustainabilty in a myriad of high-tech applications.

cond-mat.soft

Inverted and programmable Poynting effects in metamaterials

The Poynting effect generically manifests itself as the extension of the material in the direction perpendicular to an applied shear deformation (torsion) and is a material parameter hard to design. Unlike isotropic solids, in designed structures, peculiar couplings between shear and normal deformations can be achieved and exploited for practical applications. Here, we engineer a metamaterial that can be programmed to contract or extend under torsion and undergo nonlinear twist under compression. First, we show that our system exhibits a novel type of inverted Poynting effect, where axial compression induces a nonlinear torsion. Then the Poynting modulus of the structure is programmed from initial negative values to zero and positive values via a pre-compression applied prior to torsion. Our work opens avenues for programming nonlinear elastic moduli of materials and tuning the couplings between shear and normal responses by rational design. Obtaining inverted and programmable Poynting effects in metamaterials inspires diverse applications from designing machine materials, soft robots and actuators to engineering biological tissues, implants and prosthetic devices functioning under compression and torsion.

cond-mat.soft