Study on humidity-thermo-force coupling of anisotropic modified couple stress Mindlin laminates on the mesoscale

Considering the anisotropic characteristics of carbon fiber reinforced composites, the couple stress theory was modified, and the loading model of microscale Mindlin laminates in a hygrothermal environment was established. The material scale parameters affected by the environment were introduced, and the governing equations and boundary conditions were solved by using the principle of virtual work. Taking the four-sided simply supported square laminate by the orthogonal layer as an example, the displacement function of the Navier solution method was set to calculate the critical loads of the Mindlin laminates in a hygrothermal environment. The results show that the critical loads of Mindlin micro-laminate are greater than those of classical macro-theory under unidirectional axial compressive loads. The scale effect strengthens with the increase of material scale parameters, and the scale effect becomes more obvious with an increase in temperature change and hygroscopic concentration. The scale effect gradually disappears with the increase of the geometric parameters of the laminate, and the model degenerates into a macroscopic model.