More Like this

1. Experimental study of elastic constants of a dense foam with weak Cosserat coupling

   https://doi.org/10.1007/s10659-018-09714-8  

   Rueger, Z. (January 2019, Journal of elasticity)

   A dense closed cell foam is studied to determine which continuum theory of elasticity is applicable. Size effects inconsistent with classical elasticity are observed. The material exhibits a characteristic length scale considerably larger, by more than a factor 6, than the largest observable structure size. The Cosserat coupling number N is shown to be small, via measurements of size effects in square section bars, comparison with size effects in round section bars, and determination of warp of a square section bar in torsion. For this material, the couple stress theory is excluded and the modified couple stress theory is excluded. Theories that force constants to their thermodynamic limits do not apply to this foam. The role of other generalized continuum theories is considered. 

   more » « less
2. Nonclassical Thermal Twist of the Chiral Gyroid Lattice

   https://doi.org/10.1002/pssb.202200338  

   DeValk, Tyler; Hestetune, Jonah; Lakes, Roderic S. (November 2022, physica status solidi (b))

   The gyroid lattice is prepared in chiral and non‐chiral forms. The chiral gyroid lattice is observed to exhibit temperature‐induced twist with the direction of twist corresponding to the sense of chirality. This effect is a nonclassical effect that cannot occur in classical elasticity or classical thermo‐elasticity but is allowable in Cosserat solids. Poisson's ratio of the gyroid is known to be about 0.3 with minimal dependence on size. In contrast to squeeze–twist coupling in which substantial size effects occur with slender specimens twisting much more than thicker ones, thermal–twist coupling exhibits opposite and less consistent size effects of much smaller magnitude. 

   more » « less
3. Validation of an Extensible Rod Model for Soft continuum Manipulators

   https://doi.org/10.1109/ROBOSOFT.2019.8722721  

   Gilbert, Hunter B.; Godage, Isuru S. (April 2019, 2019 2nd IEEE International Conference on Soft Robotics (RoboSoft))

   Numerous soft and continuum robotic manipulators have demonstrated their potential for compliant operation in highly unstructured environments or near people. Despite their recent popularity, modeling of their smooth bending deformation remains a challenge. For soft continuum manipulators, the widespread, constant curvature approach to modeling is inadequate for modeling some deformations that occur in practice, such as combined bending and twisting deformations. In this paper, we extend the classical Cosserat rod approach to model a variable-length, pneumatic soft continuum arm. We model the deformation of a pneumatically driven soft continuum manipulator, and the model is then compared against experimental data collected from a three degree of freedom, pneumatically actuated, soft continuum manipulator. The model shows good agreement in capturing the overall behavior of the bending deformation, with mean Euclidean error at the tip of the robot of 2.48 cm for a 22 cm long robot. In addition, the model shows good numerical stability for simulating long duration computations. 

   more » « less
4. Bifurcations of an elastic disc coated with an elastic inextensible rod

   https://doi.org/10.1098/rspa.2023.0491  

   Gaibotti, M; Mogilevskaya, S G; Piccolroaz, A; Bigoni, D (January 2024, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences)

   An analytical solution is derived for the bifurcations of an elastic disc that is constrained on the boundary with an isoperimetric Cosserat coating. The latter is treated as an elastic circular rod, either perfectly or partially bonded (with a slip interface in the latter case) and is subjected to three different types of uniformly distributed radial loads (including hydrostatic pressure). The proposed solution technique employs complex potentials to treat the disc’s interior and incremental Lagrangian equations to describe the prestressed elastic rod modelling the coating. The bifurcations of the disc occur with modes characterized by different circumferential wavenumbers, ranging between ovalization and high-order waviness, as a function of the ratio between the elastic stiffness of the disc and the bending stiffness of its coating. The presented results find applications in various fields, such as coated fibres, mechanical rollers, and the growth and morphogenesis of plants and fruits. 

   more » « less
5. Intervertebral Disc Mechanics With Nucleotomy: Differences Between Simple and Dual Loading

   https://doi.org/10.1115/1.4050538  

   Yang, Bo; Klineberg, Eric; O'Connell, Grace D. (August 2021, Journal of Biomechanical Engineering)

   null (Ed.)

   Abstract Painful herniated discs are treated surgically by removing extruded nucleus pulposus (NP) material (nucleotomy). NP removal through enzymatic digestion is also commonly performed to initiate degenerative changes to study potential biological repair strategies. Experimental and computational studies have shown a decrease in disc stiffness with nucleotomy under single loading modalities, such as compression-only or bending-only loading. However, studies that apply more physiologically relevant loading conditions, such as compression in combination with bending or torsion, have shown contradicting results. We used a previously validated bone–disc–bone finite element model (Control) to create a Nucleotomy model to evaluate the effect of dual loading conditions (compression with torsion or bending) on intradiscal deformations. While disc joint stiffness decreased with nucleotomy under single loading conditions, as commonly reported in the literature, dual loading resulted in an increase in bending stiffness. More specifically, dual loading resulted in a 40% increase in bending stiffness under flexion and extension and a 25% increase in stiffness under lateral bending. The increase in bending stiffness was due to an increase and shift in compressive stress, where peak stresses migrated from the NP–annulus interface to the outer annulus. In contrast, the decrease in torsional stiffness was due to greater fiber reorientation during compression. In general, large radial strains were observed with nucleotomy, suggesting an increased risk for delamination or degenerative remodeling. In conclusion, the effect of nucleotomy on disc mechanics depends on the type and complexity of applied loads. 

   more » « less