INTERLAMINAR SCALE EFFECT OF MULTILAYER COMPOSITE MICROBEAMS BASED ON A NEW MODIFIED COUPLE-STRESS THEORY AND THE HU-WASHIZU VARIATIONAL THEOREM

Few studies on the interlaminar scale effect of multilayer composite beams are reported in the published literature. Thus, a refined higher-order zigzag model satisfying the transverse shear traction-free condition is proposed for analysis of the interlaminar scale effect of composite microbeams. The number of unknown parameters in the proposed model is independent of the number of layers. Moreover, there are only four displacement parameters in the displacement field. Differing from previous work, a three-dimensional equilibrium equation including the scale effect is proposed to accurately predict the interlaminar scale effect. It is significant that the higher-order derivatives of the displacement parameters are eliminated from the transverse shear stress components by using the three-field Hu-Washizu variational principle. By analyzing the bending behaviors of microscale composite beams, the effects of the microlength-scale parameter in each ply on the displacements and the stress of the multilayer composite beams have been investigated. The numerical results showed that with an increase in the material length constants, displacements, and in-plane stress gradually decrease, whereas the transverse shear stress at different layers does not completely decrease. Thus, the interlaminar scale effects of composite microbeams differ from those of displacements and in-plane stresses. With an increase in the number of layers, the effects of the microlength-scale length parameter on the displacements and interlaminar stresses gradually decrease.