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Abstract:
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The research presented in this thesis focuses on the modeling , design , and experimentation of systems containing negative stiffness mechanisms for both vibration and shock isolation . The negative stiffness element studied in this research is an axially compressed beam . If a beam is axially compressed past a critical value , it becomes bistable with a region of negative stiffness in the transverse direction . By constraining a buckled beam in its metastable position through attaching a stiff linear spring in mechanical parallel , the resulting system can reach a low level of dynamic stiffness and therefore provide vibration isolation at low frequencies , while also maintaining a high load -carrying capacity . In previous research , a system containing an axially compressed beam was modeled and tested for vibration isolation [7] . In the current research , variations of this model were studied and tested for both vibration and shock isolation . Furthermore , the mathematical model used to represent the compressed beam in [7] was improved and expanded in current research . Specifically , the behavior exhibited by buckled beams of transitioning into higher -mode shapes when placed under transverse displacement was incorporated into the model of the beam . The piecewise , nonlinear transverse behavior exhibited by a first -mode buckled beam with a higher -mode transition provides the ability of a system to mimic an ideal constant -force shock isolator .
Prototypes manufactured through Selective Laser Sintering were dynamically tested using a shaker table . Vibration testing confirmed the ability of a system containing a constrained negative stiffness element to provide enhanced vibration isolation results with increasing axial compression on a beam . However , the results were limited by the high sensitivity of buckled beam behavior to geometrical and boundary condition imperfections . Shock testing confirmed the ability of a system containing a buckled beam with a higher -mode transition to mimic the theoretically ideal constant -force shock isolator . |