Improved high order analysis of sandwich beams by considering a bilinear elasto-plastic behavior of core: An analytical and experimental investigation

• Initial plastic regions are detected accurately.
• The plastic regions based on combined bilinear constitutive relations of normal and shear stresses analysis of the core spread.
• The displacement components increase as the plastic modules decreases.
• The absolute value of transverse normal and shear stresses decrease in the plastic zones.

Nonlinear material response of a sandwich beam with bilinear elasto-plastic constitutive relations for the transverse normal and shear stresses of the core is studied based on a proposed improved high order sandwich panel theory (IHSAPT). In this theory the face sheets follow the first order shear deformation theory (FSDT). Besides, the two dimensional elasticity is used for the core. In this work, the behavior of the faces follows the linear elastic assumption. The field equations are derived via the Ritz based solution which is suitable for any essential boundary condition. The influences of boundary conditions on bilinear material response of the sandwich panel are investigated. In each type of boundary condition the effects of plastic modulus of the core on transverse normal stress distribution within the core, transverse shear stress, and displacement components through the thickness of the core as well as the force and moment resultants and transverse displacements in the face sheets are studied in detail. Finally, some experiments have been carried out under conditions of three point bending on sandwich beams. Load–midspan displacement predicted by analytical model based on assumed bilinear material behavior of the core is in good agreement with that obtained by experimental result. Besides, for the case study of the three point bending, the results of the constitutive model are compared with finite element simulation.