Bending analysis of bi-directional functionally graded Euler-Bernoulli nano-beams using integral form of Eringen\'s non-local elasticity theory

The main aim of this paper is to investigate the bending of Euler-Bernouilli nano-beams made of bi-directional functionally graded materials (BDFGMs) using Eringen\'s non-local elasticity theory in the integral form with compare the differential form. To the best of the researchers\' knowledge, in the literature, there is no study carried out into integral form of Eringen\'s non-local elasticity theory for bending analysis of BDFGM Euler-Bernoulli nano-beams with arbitrary functions. Material properties of nano-beam are assumed to change along the thickness and length directions according to arbitrary function. The approximate analytical solutions to the bending analysis of the BDFG nano-beam are derived by using the Rayleigh-Ritz method. The differential form of Eringen\'s non-local elasticity theory reveals with increasing size effect parameter, the flexibility of the nano-beam decreases, that this is unreasonable. This problem has been resolved in the integral form of the Eringen\'s model. For all boundary conditions, it is clearly seen that the integral form of Eringen\'s model predicts the softening effect of the non-local parameter as expected. Finally, the effects of changes of some important parameters such as material length scale, BDFG index on the values of deflection of nano-beam are studied.