Thermal-mechanical coupling buckling analysis of porous functionally graded sandwich beams based on physical neutral plane

Porosity of functionally graded materials (FGMs) is usually aroused by fabrication defects. It had been proven that the porosity has a significant influence on the static responses of their structures, but the effects of porosity on buckling behaviors are still worth investigating. To reveal these effects, the thermal-mechanical coupling buckling issue of a clamped-clamped porous FGM sandwich beam is investigated in this paper by employing the high-order sinusoidal shear deformation theory. The modified Voigt mixture rule is used to approximate the temperature-dependent material properties of porous FGMs. The physical neutral plane of FGM sandwich beams is taken into account to reflect the actual condition of the structures and simplify the calculation. The thermal environments are considered as uniform, linear and nonlinear temperature rises, and both the temperature independent and temperature-dependent material properties are discussed in order to justify the importance of the thermal-mechanical coupling effect. An iterative algorithm is used to solve the thermal-mechanical coupling critical buckling temperature. The present theoretical results are verified by comparing with the literature and ABAQUS results, and the effects of porosity, the physical neutral plane, gradient index, material temperature dependence, sandwich structural parameters are discussed. Results show that for buckling issue excluding the pre-buckling deformation effect, considering either the physical neutral plane or the geometrical middle plane of FGM beams would produce alike critical buckling temperatures. With the rise of porosity, the critical temperature increases greatly, which is quite different from the changing rule observed in the buckling issue of inplane-loaded porous FGM plates in literature. The beam with a smaller face-to-core ratio is more sensitive to the change in porosity. Moreover, to improve the thermal buckling load of FGM beams, ceramic constituents with the lower thermal expansion coefficient would be preferred.