Toughening effect of non-periodic fiber distribution on crack propagation energy of UHTC composites.

Abstract Different configurations of continuous carbon fiber-reinforced ultrahigh temperature ceramics (UHTCs), by combining coatings and matrix, were produced via electrophoretic deposition (EPD) and slurry infiltration. The toughening of non-periodic fiber distribution induced by the EPD process was investigated through work of fracture analysis. The results show that a non-periodic fiber distribution results in toughness increase from 8 MPa√m to 11 MPa√m with respect to a periodic fiber distribution. This toughness improvement does not strongly affect the flexural strength, which is mainly related to the fiber volumetric amount. It is shown that the assembling of carbon fibers into bundles (i.e. by dispersing the fibers with a non-periodic distribution) increases the crack propagation energy dissipated on the crack-wake from 0.5 kJ/m2 to 1 kJ/m2, which can be mainly ascribed to the fiber/bundle pull-out. On the other hand, the energy dissipated on the crack-tip (as fiber/matrix debonding) is fiber distribution-independent and increases from 0.3 kJ/m2 to 0.4 kJ/m2 with increasing the fiber amount from 33 vol% to 40 vol%. Finally, WoF analysis is proposed as test to evaluate pull-out toughening instead of push-in and push-out tests. Graphical abstract Image 1 Highlights • Electrophoretic deposition (EPD) of ZrB 2 and TiB 2 coating on carbon fabrics is shown. • ZrB 2 and TiB 2 coatings withstand subsequent manufacturing steps of UHTCMCs. • The EPD derived samples show a non-periodic carbon fiber distribution. • Toughness is sensitive to the degree of fiber distribution, whereas strength is not. • The crack shielding is enhanced by a non-periodic distribution of the fibers. [ABSTRACT FROM AUTHOR]