Mechanical methods to determine layer compliances within multilayered composites

Abstract

A comparison of bending and compressive/tensile loading cases of multilayered composites is given. Bending perpendicular to the layer interfaces is suggested as a sensitive and experimentally convenient method for determining the elastic modulus of compliant isotropic layers within a multilayered composite. Different approaches to analyze the strain and compliance behavior of the composite and individual layers are derived. Ranking of the relevant equations with respect to strain sensitivity is made, which favors the bending test perpendicular to the layer interfaces. The derived relationships permit a prediction of the bending behavior and the flexural rigidity of the composite. Furthermore, the properties of a layer within the structure can be determined. Limitations that exist for the bending perpendicular to the layer interfaces in the case of low stiffness of the layers can be overcome using either a compressive or a tensile loading mode. Application of the formulas to buckling and interfacial delamination is considered. Materials, such as plasma-sprayed thermal barrier coatings, that are supposed to behave elastically different in tension and compression are given special consideration. Although determination of elastic moduli is the main interest, in the case of known elastic moduli, the formulas can be used to determine the thickness of individual layers within a composite structure.