Dynamic stability analysis of porous functionally graded beams under hygro-thermal loading using nonlocal strain gradient integral model

We present a study on the dynamic stability of porous functionally graded (PFG) beams under hygro-thermal loading. The variations of the properties of the beams across the beam thicknesses are described by the power-law model. Unlike most studies on this topic, we consider both the bending deformation of the beams and the hygro-thermal load as size-dependent, simultaneously, by adopting the equivalent differential forms of the well-posed nonlocal strain gradient integral theory (NSGIT) which are strictly equipped with a set of constitutive boundary conditions (CBCs), and through which both the stiffness-hardening and stiffness-softening effects of the structures can be observed with the length-scale parameters changed. All the variables presented in the differential problem formulation are discretized. The numerical solution of the dynamic instability region (DIR) of various bounded beams is then developed via the generalized differential quadrature method (GDQM). After verifying the present formulation and results, we examine the effects of different parameters such as the nonlocal/gradient length-scale parameters, the static force factor, the functionally graded (FG) parameter, and the porosity parameter on the DIR. Furthermore, the influence of considering the size-dependent hygro-thermal load is also presented.