In situ study of fracture mechanisms in advanced ceramics using fluorescence and Raman microprobe spectroscopy

Abstract

A procedure is described for the evaluation of the fracture behaviour of polycyrstalline ceramics using an in-situ stress analysis involving either fluorescence or Raman microprobe spectroscopy. The full details of the experimental set-up, calibration procedures and stress calculations are shown, and their reliability discussed in some detail. Stress maps were obtained along the wake of cracks stably propagated in six selected polycrystalline ceramics with representative microstructures. A conventional fracture mechanics assessment was concurrently performed to relate microscopic stress data to the macroscopic fracture resistance of the materials. It is demonstrated that the most effective toughening mechanism in polycrystalline ceramics takes place in the crack wake and arises from both elastic and frictional shielding tractions operated by crystallites which are left unfractured behind the crack tip.

Raman Microprobe Evaluation of Bridging Stresses in Highly Anisotropic Silicon Nitride

“…The Raman spectroscopic apparatus (ISA, T64000 Jovin-Yvon) was used for measuring microscopic stress fields as detected from the Raman bands of silicon nitrides. The experimental procedure of the in situ Raman experiments on the crack profile have been reported in detail in two previous reports, 9,20 but are briefly described here. An Ar-ion laser operating at a wavelength of 488 nm, with a power of 300 mW, was used as the excitation source for the Raman experiments.…”

“…For the calibration, unnotched Si 3 N 4 bars were mounted on a four-point bending jig manually loaded through a load cell, which was in turn placed into the Raman microprobe device (a complete draft of the calibration setup has been given in Ref. 20). As far as the ceramic bar can be considered to deform in elastic fashion, applied stresses along the bar thickness can be regarded as uniaxial and linearly changing from compression to tension, with the zero stress placed at the center of the bar.…”

Raman Spectroscopic Analysis of Advanced Ceramic Composite for Hip Prosthesis

“…Raman and fluorescence spectroscopies are versatile and rapid methods for analyzing the presence of different polymorphs and residual mechanical stress in bulk ceramic materials with a high spatial resolution. 7,8 The Raman method is noncontact, non-destructive, and requires no special preparation or manipulation of the sample, all these being useful characteristics for application to the characterization of hip joints. Modern Raman spectrometers may achieve a micrometer-scale spatial (lateral) resolution because they utilize a conventional metallurgical (optical) microscope to guide the exciting laser beam onto the sample and subsequently to collect the Raman (or fluorescence) scatter.…”

Raman piezospectroscopic evaluation of intergrowth ferroelectric polycrystalline ceramic in biaxial bending configuration

“…17,18 The origin of the PS effect is the change of the energy of the electron or phonon transition state in the solid due to the applied stress. 19 From a theoretical viewpoint, the relationship between the spectral shift and the stress can be described by a Taylor's series expansion, as follows:…”