Use of focused ion beam (FIB) for advanced interpretation of microindentation test results applied to cementitious composites

The paper presents results of pilot trials of using the focused ion beam (F IB) technique in the framework of methods for assessment of micromechanical properties of cementitious composites. FIB is already being used in other applications, namely for the purpose of micromachining (e.g, repairs of int egrated circuits, production of diode laser mirrors etc.). Its previous use by the authors for micro-machining of diamond probes tailor-made for push- out tests of 10 mu m diameter glass fibres has been extended to include inv estigation of the microindentation test method itself. Using FIB etching, c ross-sections through indents have been produced by removal of material in the shape of a wedge from one side of the section. The plane of the vertica l "wall" of this wedge-shape recess is positioned to intersect the centre o f the indent thus revealing the hitherto unavailable direct view of the mic rostructure of material directly below and around the microindents. The cro ss-section(s) provides fundamental information about: the possible fracture modes induced by the impression of the diamond probe in the surrounding ma terial. The availability of such "third dimension" of the indentation test provides a more realistic assessment of the sub-surface "support conditions " around the points of micro-indentation and a much better interpretation o f the results derived from the displacement/load diagram monitored during t he indentation test.