A novel trench fibre push-out method to evaluate interfacial failure in long fibre composites

Published in the Journal of Materials Research by the OMG group.  Traditional fibre push-outs for the evaluation of interfacial properties in long fibre ceramic matrix composites present their limitations; solutions for which are addressed in this work by introducing the novel trench push-out test. 

The trench push-out makes se of a FIB milling system and an SEM in-situ nanoindenter to probe a fibre pushed into a trench underneath, allowing in-situ observations to be directly correlated with micromechanical events.

SiCf/BN/SiC composites - candidate materials for turbine engines - were used as model materials in this work.  Different fibre types (Hi-Nicalon and Tyranno type SA3) were coated with BN interphases, presenting mean interfacial shear stresses of  14 + 7 MPa and 20 + 2 MPa, respectively, during fibre sliding.

The micromechanical technique enabled visualisation of how defects in the interphase (voids, inclusions and milled notches) or in the fibre (surface asperities, non-uniform coatings) affected the variability of interfacial property measurement.