Study of micro-mechanical properties of sea-shell and cement paste using express nanoindentation mapping

Over the past two decades nanoindentation technique has been increasingly used to study mechanical properties of micro-structural features in many natural and engineering materials. In the case of nano-composites, such as sea shells and cement paste, mapping of mechanical properties at the micro/nano scale and the associated statistical nanoindentation technique has been developed to visualise and characterise the mechanical properties of the complex microstructural features. Mapping mechanical properties using conventional nanoindentation technique, though a proven valuable method, does have a number of limitations for studying complex, heterogeneous, nano-composite materials. One particular limitation is its relatively slow test speed: typically it takes about 8 minutes to complete one indentation test point, or more than 24 hours continuous testing to cover 200 test points. As a result, insufficient number of test points often leads to poor quality (e.g. low resolution and unrepresentative) of the mechanical properties map generated and unreliable or erroneous results obtained from the statistical analysis.

This paper reports recent studies carried out using the new Express nanoindentation mapping technique developed by Keysight technologies, which offers test speed up to 500 times faster than the conventional method. High resolution mechanical properties mapping (with nearly 10000 test points) of a sea shell specimen reveals that the marine organisms exert exquisite control on mineral formation by tuning structural and material properties to meet functional requirements. Significantly increased number of test points can also benefit characterisation of cement paste specimens using the statistical analysis.