Enhanced core rigidity classifier method (RJS 2.0): A comprehensive approach to properly measure elastic properties of sandwich structures

The primary RJS Method consists of a suggestive criterion for the qualitative and quantitative classification of the core rigidity relevance in sandwich panels based on the structure's ability to achieve pure bending behaviour. It also includes a set of assumptions that address the influence of the dimensions of the specimen on the elastic properties measured by three-point bending tests. The method allows for characterising the flexural modulus of sandwich panels through a homogenisation concept and comparing theoretical and experimental values to assess the amount of shear deformations occurring. Some limitations of the method were reported, such as the restriction to three-point bending tests and symmetrical sandwich structures (those composed of faces of the same thickness and composition). Additionally, the possible contribution of the rigidity of the face-to-core adhesives was not addressed when estimating the overall rigidity of a sandwich panel. Moreover, a direct link between the qualitative and quantitative classifications of core rigidity relevance was not achieved. In this new enhancement approach, called the RJS Method 2.0, not only are faces of different thicknesses and compositions addressed, but also the mechanical contribution of the face-to-core bonding when adhesives with relative thickness and rigidity are used. The new equations also cover four-point bending tests and clarify a direct association between the qualitative and quantitative classifications of core rigidity relevance. To facilitate the theoretical calculation of all equations, a MATLAB script is proposed. The outputs of the script are thoroughly compared to numerical results and data available in the literature, demonstrating the proper accuracy of the RJS Method 2.0 in predicting the elastic properties of sandwich structures under bending.