EXTRACTING IN-SITU THE MECHANICAL PROPERTIES OF THE POLIMERIC MATRIX IN COMPOSITES THROUGH IN-SITU NANOINDENTATION TESTS.

The nanoindentation technique is a unique experimental method to extract in-situ the mechanical properties of the matrix and the matrix-fiber interface in a composite material. However, although many studies have been carried out with the objective of extracting mechanical properties through indentation in cohesive elasto-plastic materials, these studies cannot be directly extended to polymers due to their frictional behavior (hydrostatic pressure dependent plasticity). The aim of this work is to carry out a thorough numerical study by Finite Element modeling of the process of sharp indentation in cohesive frictional materials. The results show that the friction angle (hydrostatic pressure dependency) has a marked influence on the loading-unloading indentation curves and on indentation pressure, but that the inverse problem (i.e. extracting the friction angle from a single indentation) is not possible without knowledge of additional information.