Narayanan Kidambi

Adaptation of Energy Dissipation in a Mechanical Metastable Module Excited Near Resonance

Recent studies have demonstrated that the energetic vibrations of strategically designed negative stiffness inclusions may lead to large and adaptable damping in structural/material systems. Many researchers examine these features using models of bistable elements. From the viewpoint of system integration, bistable, negative stiffness elements often interface with positive stiffness elastic members. Under such conditions, the structural/material system may exhibit coexisting metastable states. In other words, the macroscopic displacement/strain remains fixed while the reaction force may vary due to internal change, similar to a phase transition. This coexistence of metastable states is not manifested in an individual (stand-alone) bistable element. Although the static and low frequency linear dynamics of structural/material systems possessing coexisting metastable states have been explored, much remains to be understood regarding the dynamics and energy dissipation characteristics of such systems when excited near resonance, where nonlinear dynamics are more easily activated and damping design is of greater importance. Thus, to effectively elucidate the enhanced versatility of damping properties afforded by exploiting negative stiffness inclusions in structural/material systems, this research investigates a mechanical module which leverages a coexistence of metastable states: an archetypal building block for system assembly. The studies employ analytical, numerical, and experimental findings to probe how near-resonant excitation can trigger multiple dynamic states, each resulting in distinct energy dissipation features. It is shown that, for lightly damped metastable mechanical modules, the effective energy dissipation may be varied across orders of magnitude via tailoring design and excitation parameters. [DOI: 10.1115/1.4031411]

Energy release for the actuation and deployment of muscle-inspired asymmetrically multistable chains

Animal locomotion and movement requires energy, and the elastic potential energy stored in skeletal muscle can facilitate movements that are otherwise energetically infeasible. A significant proportion of this energy is captured and stored in the micro- and nano-scale constituents of muscle near the point of instability between asymmetric equilibrium states. This energy may be quickly released to enable explosive macroscopic motions or to reduce the metabolic cost of cyclic movements. Inspired by these behaviors, this research explores modular metastructures of bistable element chains and develops methods to release the energy stored in higher-potential system configurations. Quasi-static investigations reveal the role of state-transition pathways on the overall efficiency of the deployment event. It is shown that sequential, local release of energy from the bistable elements is more efficient than concurrent energy release achieved by applying a force at the free end of the structure. From dynamic analyses and experiments, it is shown that that the energy released from one bistable element can be used to activate the release of energy from subsequent links, reducing the actuation energy required to extend or deploy the chain below that required for quasi-static deployment. This phenomenon is influenced by the level of asymmetry in the bistable constituents and the location of the impulse that initiates the deployment of the structure. The results provide insight into the design and behavior of asymmetrically multistable chains that can leverage stored potential energy to enable efficient and effective system deployment and length change.

Multistability inspired by the oblique, pennate architectures of skeletal muscle

Skeletal muscle mechanics exhibit a range of noteworthy characteristics, providing great inspiration for the development of advanced structural and material systems. These characteristics arise from the synergies demonstrated between muscle’s constituents across the various length scales. From the macroscale oblique orientation of muscle fibers to the microscale lattice spacing of sarcomeres, muscle takes advantage of geometries and multidimensionality for force generation or length change along a desired axis. Inspired by these behaviors, this research investigates how the incorporation of multidimensionality afforded by oblique, pennate architectures can uncover novel mechanics in structures exhibiting multistability. Experimental investigation of these mechanics is undertaken using specimens of molded silicone rubber with patterned voids, and results reveal tailorable mono-, bi-, and multi-stability under axial displacements by modulation of transverse confinement. If the specimen is considered as an architected material, these results show its ability to generate intriguing, non-monotonic shear stresses. The outcomes would foster the development of novel, advanced mechanical metamaterials that exploit pennation and multidimensionality.

Energy dissipation characteristics of a mechanical metastable module excited near resonance

Recent studies have demonstrated that the energetic vibrations of strategically designed negative stiffness inclusions may lead to large and adaptable damping in structural/material systems. Many researchers examine these features using models of bistable elements. From the viewpoint of system integration, bistable, negative stiffness elements often interface with positive stiffness elastic members. Under such conditions, the structural/material system may exhibit coexisting metastable states. In other words, the macroscopic displacement/strain remains fixed while the reaction force statically and/or dynamically varies due to internal change similar to a phase transition. This coexistence of metastable states is not manifested in an individual (stand-alone) bistable element. Although the static and low frequency dynamics of structural/material systems possessing coexisting metastable states have been explored, much remains to be understood regarding the dynamics and energy dissipation characteristics of such systems when excited near resonance, where nonlinear dynamics may be more easily activated and damping design is of great importance. Thus, to effectively elucidate the enhanced versatility of damping properties afforded by exploiting negative stiffness inclusions in structural/material systems, this research investigates a mechanical module which leverages a coexistence of metastable states: an archetypal building block for system assembly. The studies employ analytical, numerical, and experimental findings to probe how near-resonant excitation can trigger multiple dynamic states, each resulting in distinct energy dissipation features. It is shown that, for lightly damped metastable mechanical modules, the effective energy dissipation may be varied across orders of magnitude via tailoring design and excitation parameters. Potential applications and prototype systems are discussed to bridge the discoveries to future practice.Copyright