A novel method for measuring residual stress is proposed and analyzed in this study. The method is based on the electromechanical bifurcation response of a clamped-clamped beam. The stressed beam is subjected to a symmetric electrostatic field. The presented analysis shows that the critical voltage which induces the bifurcation response is a monotonic function of the residual stress. Furthermore, the electromechanical bifurcation occurs for both compressive and tensile residual stresses. Ensuring that the postbuckling response is non-stable facilitates the identification of the bifurcation response. To this end, geometrical conditions are derived which ensure that the postbuckling state of the system is non-stable. It is shown that a single test structure can be used to measure residual stress in a continuous wide range.

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A first-ever experimental validation of the electromechanical buckling response is presented. Electromechanical buckling is the coupling of two bifurcation responses: mechanical buckling and electromechanical bifurcation. In this paper, electromechanical buckling is demonstrated on a clamped-guided beam that is simultaneously subjected to an axial mechanical load and a symmetric, transverse, electrostatic field. Experimental measurements of the electromechanical buckling voltage are in good agreement with the theoretical prediction.[ 2006-0023]Index Terms-Electromechanical buckling, electromechanical instability.

As a member of the smart polymer material group, stimuli responsive hydrogels have achieved a wide range of applications in microfluidic devices, micro/nano bio and environmental sensors, biomechanics and drug delivery systems. To optimize the utilization of a hydrogel in various micro and nano applications it is essential to have a better understanding of its mechanical and electrical properties. This paper presents a review of the different techniques used to determine a hydrogel's mechanical properties, including tensile strength, compressive strength and shear modulus and the electrical properties including electrical conductivity and dielectric permittivity. Also explored the effect of various prototyping factors and the mechanisms by which these factors are used to alter the mechanical and electrical properties of a hydrogel. Finally, this review discusses a wide range of hydrogel fabrication techniques and methods used, to date, to actuate this family of smart polymer material.

In this work, a new test structure and method for measuring residual stress is presented. The test structure is a single clamped-clamped beam with electrodes symmetrically positioned along both sides of the beam. The electromechanical buckling response is used to measure the residual stress. It is shown that a single test structure of the proposed design may be used to measure both compressive and tensile residual stresses in a continuous wide range.