Generalized thermoelasticity model of nonlocal strain gradient Timoshenko nanobeams

The aim of this study is to establish a thorough model for appraisal of size-dependent thermoelastic vibrations of Timoshenko nanobeams by capturing small-scale effect on both structural and thermal fields. With the intention of incorporating size effect within motion and heat conduction equations, nonlocal strain gradient theory (NSGT) as well as nonclassical heat conduction model of Guyer and Krumhansl (GK model) are exploited. For the sake of generalization and clarifying the impact of nonclassical scale parameters on results, by introducing some nondimensional quantities, the size-dependent coupled thermoelastic equations are written in dimensionless form. By applying the Laplace transform to this system of differential equations, thermoelastic responses of a simply supported Timoshenko nanobeam under dynamic load are extracted in closed forms. In order to highlight the influence of scale parameters on thermoelastic behavior of Timoshenko nanobeams, a variety of numerical results is provided. The discrepancy between classical and nonclassical outcomes betokens the salient role of structural and thermal scale parameters in accurate analysis of nanobeams. In addition, findings reveal that utilization of NSGT gives the means to capture both stiffness softening and stiffness enhancement characteristic of small-sized structures, so that according to the relative values of two scale parameters of NSGT, the nonclassical model of Timoshenko nanobeam can exhibit either softening or hardening behavior in comparison with the classical one.