Browsing by Author "Sapsathiarn, Y"

Filter results by typing the first few letters
Now showing 1 - 3 of 3
  • Thumbnail Image
    PublicationEmbargo
    Mechanistic models for nanobeams with surface stress effects
    (American Society of Civil Engineers, 2018-11-01) Sapsathiarn, Y; Rajapakse, R. K. N. D
    In this paper, a mechanistic model for nanobeams with surface energy effects is developed by using a variational formulation. Thiswork is motivated by the unusual response of nanocantilevers predicted by models based on the Young-Laplace equation for surface stress.The governing equation and boundary conditions derived from the variational methods are compared with the governing equations andboundary conditions used in the Young-Laplace models and other formulations. A key difference in the shear force boundary condition isnoted. Analytical solutions for simply supported, cantilevered, and fixed-fixed beams are reexamined. It is shown that the unusual behavior ofnanocantilevers predicted by the Young-Laplace models is due to the shear force boundary condition used. The current formulation leads toconsistent solutions for beams under different boundary conditions.DOI:10.1061/(ASCE)EM.1943-7889.0001520.© 2018 AmericanSociety of Civil Engineers
  • Thumbnail Image
    PublicationOpen Access
    Numerical modelling of piezoelectric actuators exposed to hydrogen
    (Springer Vienna, 2014-10) Sapsathiarn, Y; Singh, Y; Rajapakse, R. K. N. D
    Modern fuel injectors have been developed based on piezoelectric stack actuators. Performance and durability of actuators in a hydrogen environment are important considerations in the development of hydrogen injectors. 2D plane stress and 3D models for analysis of coupled diffusion and thermo-electromechanical response of actuators are presented. Chemical potential, electric field and temperature gradients are taken as driving forces for hydrogen transport. The explicit Euler finite difference method is used to solve the nonlinear diffusion governing equation. The finite element method is used for time-dependent analysis of fully coupled mechanical, electric and thermal fields. The diffusion process and thermo-electromechanical deformations are coupled through the dependence of piezoelectric properties on hydrogen concentration. Experimental results for the piezoelectric coefficient d 33 of PZT ceramics exposed to different hydrogen concentrations are used. A comparison of a fully coupled 2D model with 2D and 3D models with reduced coupling is made to examine the significance of coupling and computational efficiency. Selected numerical results are presented for time histories of hydrogen concentration, temperature and stroke of an idealized actuator unit cell to obtain a preliminary understanding of the performance of actuators exposed to hydrogen.
  • Thumbnail Image
    PublicationEmbargo
    Static and dynamic analyses of nanoscale rectangular plates incorporating surface energy
    (Springer Vienna, 2017-08) Sapsathiarn, Y; Rajapakse, R. K. N. D
    In this paper, the Gurtin–Murdoch continuum theory is applied to develop a new continuum mechanics model for static and dynamic analyses of nanoscale rectangular plates. The relevant governing equations are established from basic principles. Analytical solutions for static and free vibration of nanoscale rectangular plates are presented for selected boundary conditions. A finite element method for the analysis of rectangular nanoplates is also developed to solve general cases that cannot be solved analytically. Expressions for stiffness and mass matrices and the load vector are derived by using a weighted residual formulation. A selected set of numerical results is presented to investigate the size-dependent static and free vibration response of plates and the influence of surface material properties and boundary conditions.