In some applications it is more interesting to look at the behavior of materials under shear force rather than normal force. In this case the nanoindentation probe can be used to form
nanoscratches.
This image shows a series of nanoscratches across a region of a polished tooth section of composite structure. The scratches are more deep in the darker regions which were assumed to be softer as more material was removed from these regions upon polishing. It is thought that these harder regions might prevent fractures from propagating through the tooth region, allowing the tooth to remain functional after a crack. The lack of material piled up on the sides of the scratch indicates that the deformation if primarily fracture and not plastic in nature.
This is a very striking demonstration of nanoscratching. A single scratch was made on a polished tooth section in the region at the interface of the enamel and dentin. A very deep trough with pile-up due to plastic deformation is seen in the dentin, while there is a very shallow scratch with very little sign of plastic deformation in the enamel, consistent with fracture deformation.
Thanks to Dr. Greg Erickson, FSU Biology.
The top image is the image of a diamond nanoindentation probe. The triangular pyramid of the diamond itself is shown. A stainless steel cantilever extends to the top right of the image. The charging region towards the upper right quadrant is an epoxy used to glue the diamond to the cantilever. The bottom image shows the functional portion of the diamond indentation surface. It was inspected in SEM to ascertain whether the structures visible in optical microscopy near the probe tip were fractures or adhered material. It is clearly debris material from a previous scratch or indentation.
