LAUSR

Abstract Elastic modulus of multiple layer two-dimensional (2D) materials is typically measured in indentation testing via existing indentation bending model of a beam/plate, in which the sample is assumed to be a doubly clamped beam/plate under a central point load. However, a paradox is commonly found in indentation testing of multiple layer 2D materials: the measured indentation load-displacement curve has a much longer linear regime than the corresponding theoretical counterpart; in addition, the elastic modulus determined is significantly lower than its theoretical counterpart. Based on the theoretical and numerical analyses, the above paradox can be well explained via the separation of the adhesive boundary of 2D materials in indentation tests, resulting in that the freestanding portion of sample behaves like a pure bending beam/plate, instead of a doubly clamped beam/plate subjected to a central point load. These results agree with the reported experimental results very well, and thus, the indentation response of multiple layer 2D materials should be analyzed via the pure bending model instead of the existing indentation bending model of beam/plate.