On the specifics of behavior of the sandwich plate composite facing layers under local loading

The problem of a four-point bending of sandwich plates with external layers of a fiber reinforced plastic is considered, the results of numerical and experimental studies are presented. It is shown that in the vicinity of the loading roller, which exerts a local effect on the external layer, there is a strong decrease in the transverse shear secant modulus of fiber reinforced plastic with an increase in the transverse shear strains. The numerical solution of the problem of the plate bending is carried out in a physically and geometrically nonlinear formulation using various relations of the finite element method, two variants of geometrically nonlinear kinematic relations of the equations of the elasticity theory and different variants of the loading process parameter. Along with the classical nonlinear relations, the problem solutions are also constructed on the basis of consistent relations between strains and displacements, the use of which allows one to avoid the appearance occurrence of false bifurcation points. The results of the numerical calculations obtained with different methods and use of different ratios are presented, the analysis of which showed their small difference. It was revealed that the stability loss and failure of the external layers of a sandwich plate occurs due to the stability loss in the nonclassical transverse-shear mode. To determine the ultimate load, which is accompanied with a loss of strength of the external loaded layer, the Tsai-Wu criterion was used. A comparative analysis of the behavior of the plate external layers at different thicknesses and different diameters of the loading roller is carried out. It is shown that the ultimate load is practically not affected by the roller diameter, while the load at which the external layer loses its stability, is very sensitive to a change in its value.