Determination of the interfacial properties of carbon fiber reinforced polymers using nanoindentation

The mechanical properties of the interphase play a key role in determining the overall performance of carbon fiber reinforced polymer (CFRP) composite materials. For this reason, it is important to develop a method to easily and precisely investigate the mechanical performance of the interphase of CFRP materials. In this work, the surface topography of the CFRP material was examined using scanning probe microscopy (SPM), which revealed the polished flat sample can meet the requirements of the nanoindentation testing. The local mechanical performance of the interphase of the CFRP was determined using nanoindentation based on the continuous stiffness measurement (CSM) method. The results show that the size of the interphase between the carbon fiber and the matrix is about 1.5 μm, and the corresponding modulus and hardness values were estimated to be 5–11 and 0.4–3.3 GPa, respectively, considering the fiber-bias effects. Mapping of the local mechanical properties of a selected area revealed that nanoindentation reproduced excellently the surface topography and characterized precisely the properties of the interphase between the carbon fibers and the matrix.