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

Abstract

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 use 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 material 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 & milled notches) or in the fibre (surface asperities, non-uniform coatings) affected the variability of interfacial property measurement. Graphic abstract

Methods and models for fibre–matrix interface characterisation in fibre-reinforced polymers: a review

“…Even if tested in an SEM, direct visualisation of crack propagation or the dominant failure mechanism is not possible. Additionally, traditional fibre push-out tests often yield a high degree of data variability, which can be better understood and mitigated through the use of innovative in-situ techniques [392]. Moreover, studies on the development of piezoelectric push-out devices have primarily focused on device production, with insufficient attention given to assessing the accuracy and analysing material failure.…”

Current trends in nanomechanical testing research

“…The most popular application in the focus issue is measuring the local fracture behavior of materials [17][18][19][20]. In addition to providing a desired complex microsample geometry, the FIB micromachining technique allows one to visualize the deformation field that would otherwise be concealed under the surface [21].…”

“…As evidenced by the high number of related contributions, the use of the FIB has become essential in the field of nanomechanical testing [17,18,[20][21][22]. This has inevitably raised concerns about possible measurement artifacts due to ion damage incurred during the specimen preparation [20,[23][24][25].…”

“…Their development has been a dominant trend in nanomechanical research throughout the past decade, with their application seemingly only being limited by the high costs associated with the techniques. This trend is continued in the focus issue, which features applications both inside scanning electron microscopes (SEM) [17,18,21,22] and transmission electron microscopes (TEM) [23,24].…”