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710 results on '"Howell, Larry L."'

222. A Pseudo-Rigid-Body Model for Large Deflections of Fixed-Clamped Carbon Nanotubes

Author

Massachusetts Institute of Technology. Department of Mechanical Engineering, Di Biasio, Christopher M, Cullinan, Michael Arthur, Panas, Robert M, Culpepper, Martin, Howell, Larry L., Massachusetts Institute of Technology. Department of Mechanical Engineering, Di Biasio, Christopher M, Cullinan, Michael Arthur, Panas, Robert M, Culpepper, Martin, and Howell, Larry L.

Abstract

Carbon nanotubes (CNTs) may be used to create nanoscale compliant mechanisms that possess large ranges of motion relative to their device size. Many macroscale compliant mechanisms contain compliant elements that are subjected to fixed-clamped boundary conditions, indicating that they may be of value in nanoscale design. The combination of boundary conditions and large strains yield deformations at the tube ends and strain stiffening along the length of the tube, which are not observed in macroscale analogs. The large-deflection behavior of a fixedclamped CNT is not well-predicted by macroscale large-deflection beam bending models or truss models. Herein, we show that a pseudo-rigid-body model may be adapted to capture the strain stiffening behavior and, thereby, predict a CNT's fixed-clamped behavior with less than 3% error from molecular simulations. The resulting pseudo-rigid-body model may be used to set initial design parameters for CNT-based compliant mechanisms. This removes the need for iterative, time-intensive molecular simulations during initial design phases. Keywords: compliant mechanism; pseudo-rigid-body; flexure; carbon nanotube; molecular simulations; nanomechanical; nanoelectromechanical

Published
2018

232. The Mixed-Body Model: A Method for Predicting Large Deflections in Stepped Cantilever Beams

Author

Sargent, Brandon, Ynchausti, Collin, Nelson, Todd G, and Howell, Larry L

Abstract

This paper presents a method for predicting endpoint coordinates, stress, and force to deflect stepped cantilever beams under large deflections. This method, the Mixed-Body Model or MBM, combines small deflection theory and the Pseudo-Rigid-Body Model for large deflections. To analyze the efficacy of the model, the MBM is compared to a model that assumes the first step in the beam to be rigid, to finite element analysis, and to the numerical boundary value solution over a large sample set of loading conditions, geometries, and material properties. The model was also compared to physical prototypes. In all cases, the MBM agrees well with expected values. Optimization of the MBM parameters yielded increased agreement, leading to average errors of <0.01 to 3%. The model provides a simple, quick solution with minimal error that can be particularly helpful in design.

Published
2021
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233. A Pseudo-Rigid-Body Model for Initially-Curved Pinned-Pinned Segments Used in Compliant Mechanisms

Author

Edwards, Brian T., Jensen, Brian D., and Howell, Larry L.

Subjects
Machinery, Kinematics of -- Research, Engineering and manufacturing industries, Science and technology
Abstract

The pseudo-rigid-body model concept allows compliant mechanisms to be analyzed using well-known rigid-body kinematics. This paper presents a pseudo-rigid-body model for initially curved pinned-pinned segments that undergo large, nonlinear deflections. The model approximates the segment as three rigid members joined by pin joints. Torsional springs placed at the joints model the segment's stiffness. This model has been validated by fabricating several such segments from a variety of different materials. Testing of the force-deflection behavior of these segments verified the accuracy of the model.

Published
2001

241. Embedded Linear-Motion Developable Mechanisms on Cylindrical Surfaces

Author

Sheffield, Jacob L., Sargent, Brandon, and Howell, Larry L.

Abstract

This study introduces methods for developing embedded straight-line and linear-motion mechanisms on right circular cylinders. Developable surfaces, particularly right circular cylinders, are the manufactured embodiment of many products. Functional linkages are traditionally not geometrically constrained to a body and often dictate the final shape of the housing they reside. This work explores mapping straight-line and linear-motion mechanisms onto cylinders for practical design. Potential applications for when an embedded cylindrical developable mechanism capable of deployment and generation of linear motion would be useful are discussed. An in vivo wiper mechanism to clean obstructed laparoscope lenses during surgery is investigated to physically demonstrate the concepts introduced in the article and to illustrate an example application.

Published
2024
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