Evaluation of Negative Stiffness Elements for Enhanced Material Damping Capacity

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Title: Evaluation of Negative Stiffness Elements for Enhanced Material Damping Capacity
Author: Kashdan, Lia Beatrix
Abstract: Constrained negative stiffness elements in volume concentrations (1 % to 2 % ) embedded within viscoelastic materials have been shown to provide greater energy absorption than conventional materials [Lakes et al . , Nature (London ) 410 , 565–567 (2001 )] . This class of composite materials , called meta -materials , could be utilized in a variety of applications including noise reduction , anechoic coatings and transducer backings . The mechanism underlying the meta -material's behavior relies on the ability of the negative stiffness element to locally deform the viscoelastic material , dissipating energy in the process . The work presented here focuses specifically on the design of the negative stiffness elements , which take the form of buckled beams . By constraining the beam in an unstable , S -shaped configuration , the strain energy density of the beam will be at a maximum and the beam will accordingly display negative stiffness . To date , physical realization of these structures has been limited due to geometries that are difficult to construct and refine with conventional manufacturing materials and methods . By utilizing the geometric freedoms allowed by the Selective Laser Sintering (SLS ) machines , these structures can be built and tuned for specific dynamic properties . The objective of this research was to investigate the dynamic behavior of SLS -constructed meso -scale negative stiffness elements with the future intention of miniaturizing the elements to create highly absorptive meta -materials . This objective was accomplished first through the development and analysis of a mathematical model of the buckled beam system . A characterization of the Nylon 11 material was performed to obtain the material properties for the parts that were created using SLS . Applying the mathematical model and material properties , a tuned meso -scale negative stiffness structure was fabricated . Transmissibility tests of the meso -scale structure revealed that the constrained negative stiffness system was able to achieve overall higher damping and vibration isolation than an unconstrained system . Quasistatic behavior of the system indicated that these elements would be ideal for implementation within meta -materials . Based on the results of the meso -scale system , a method to test a representative volume element for a negative stiffness meta -material was developed for future completion .
URI: http : / /hdl .handle .net /2152 /ETD -UT -2010 -05 -1301
Date: 2010-10-29


Evaluation of Negative Stiffness Elements for Enhanced Material Damping Capacity. Master's thesis, University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /ETD -UT -2010 -05 -1301 .

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