Direct measurement of fiber bridging in notched glass-ceramic-matrix composites

Abstract

A novel, high-resolution remote Raman microscope was used for the direct in situ assessment of deformation on bridging fibers in a double-edge-notched SiC-Nicalon reinforced ceramic-glass matrix composite at various stages of monotonic tensile loading. The effect of notch length on the bridging strain profiles obtained by individually probing a large number of fibers across the bridged ligament of the composite was investigated. Bridging strain measurements in the microscale are used to identify the role and sequence of the failure micromechanisms developing within the bridging zone and are compared with their macromechanically derived counterparts. The difference of 25% in failure strain between the as-received fiber and the maximum value obtained on composite-fibers through laser Raman microscopy (LRM), is attributed to the different patterns of fiber failure in composites as compared to the techniques used for fibers characterization such as monofilament and bundle testing in air. This article demonstrates how the LRM-strain data can be utilized to obtain a direct, microscale measure of the interfacial-shear strength of the composite. The obtained interfacial shear strength (ISS) value of 7 MPa compares well with the macromechanically predicted value and offers a much higher precision compared to other experimental techniques.

A geometry-invariant fracture law for ceramic matrix composites

“…The fracture behavior of the particular composite has been found to be consistent with the formation of a dominant macrocrack that starts at the notch root and propagates within the material to give rise to intefacial debonding, fiber bridging, sliding, and pullout. 14,17 The behavior was verified for the SENB geometry of the current study by post-mortem observations of the failed ligaments of the samples after three point bending tests. As seen in Figure 2, material fracture is associated with the formation of a dominant macrocrack around which energy dissipation mechanisms such as fiber bridging and pull-out evolve.…”

“…The instantaneous crack length, D, and COD at x ¼ 0 , max would be measured using an inline microscope with a known stepmotion capability. 17 Assuming a symmetric triangular bridging zone shape (isosceles triangle), slope c was calculated from the result of the division max /D.…”

Internal residual stresses in glass-ceramics: A review

“…In another study, Dassios et al [57,58] used in situ Raman spectroscopy to study the mechanical behavior of SiC fibers in a LiO 2 -MgO-Al 2 O 3 -SiO 2 glass-ceramic matrix under tensile loading. Strain profiles along individual fibers at different loading stages were measured.…”

Matrix modification of laminated SiCw/SiC ceramic composites

“…Comparing with the composites without modification (Figure 6(a)), the composites modified by PIP exhibited longer crack prorogation path and more crack deflection along with the interlaminar (Figure 6(b)). 12 The crack can be effectively deflected in the interlaminar, indicating that the interlaminar bonding strength was not increased after PIP process.…”