Theoretical analyses and numerical simulations on the mechanical strength of multilayers subjected to ring-on-ring tests

Biaxial flexure tests have been applied widely to measure the strength of monolithic linear elastic materials. In spite of the increasing applications of multilayered composite materials, the theoretical description on their strengths using biaxial flexure tests seems very difficult and the relative fracture load-biaxial strength relationship for multilayered discs subjected to biaxial moment is still unavailable. In this paper, the advanced solutions for the elastic stress distribution in thin multilayered discs subjected to biaxial bending moment have been derived. We find the convertible relationship between monolayered and multilayered discs subjected to ring-on-ring tests. To evaluate the accuracy of the solutions, finite element analyses (FEA) are further performed on monolayered, bilayered with different thickness ratios and trilayered discs, respectively. In stress distribution results, we present stress gradient existing at the interface, which can harmonize the bilayered systems in our model. The present simple closed-form solutions can allow the biaxial strength of multilayered systems to be evaluated.