Cr3+ microspectroscopy measurements and modelling of local variations in surface grinding stresses in polycrystalline alumina

High resolution optical microprobe investigation of surface grinding stresses in Al2O3 and Al2O3/SiC nanocomposites

“…The procedure for grinding of the specimens followed our previous work [25]. Specimens were sequentially polished down to a 1 m diamond finish first to start from smooth surfaces, and they were then ground on a resin bonded alumina wheel for [12]: (i) "ground" regions, which are relatively flat and which, when examined in the scanning electron microscope (SEM), show scratches produced by plastic deformation of the surface [12] and (ii) "pullouts", where a piece of material has been removed from the surface by brittle fracture around its periphery.…”

“…In this work, confocal Cr 3+ fluorescence microscopy was used, with lateral and axial (depth) resolutions of ∼1.5 m and ∼3 m, respectively [21,22]. Previous work on alumina based materials using Cr 3+ fluorescence microscopy investigated only residual stresses induced by indentation or scratching [23,24]; in addition, it used weakly confocal microscopes with depth resolution of ∼10 m. From both TEM observations [18] and results in our previous work [25], it is known that grinding stresses are expected to be found at depths of ∼1 m for monolithic alumina. Considering the translucency of alumina materials, therefore, the conclusion in Ref.…”

“…The experimentally measured stress is actually the convolution of the real stress with the axial probe response function (PRF) [26] which describes the relative collection efficiency as a function of depth and depends on the instrument and the translucency of the material. In our previous work, on ground surfaces of alumina, residual stress distributions were estimated by modelling the plastic displacement of material resulting from grinding as an array of continuously distributed edge dislocations [21,25], and established the PRF of our instrument when used with Al 2 O 3 and Al 2 O 3 /SiC [21,22]. The convolution of the fluorescence response predicted by the model with the PRF allowed the local residual stress variation for polycrystalline alumina after grinding and polishing to be estimated by adjusting the physical parameters in the model to fit the experimental results.…”

Transient and residual stresses in a pressable glass–ceramic before and after resin–cement coating determined using profilometry

“…The grinding process was multidirectional owing to the rotational aspect of the machine during grinding, such that machining induced cracks and residual stresses are difficult to asses so that the nature of the interaction between these opposing factors is unclear in the ceramic literature. [38][39][40][41] Interestingly, for the three experimental groups of 0.61 AE 0.05, 0.84 AE 0.08, and 1.06 AE 0.07 mm no significant difference in baseline quantification of the mean of the maximum deflection between specimens groups was evident. The polishing procedure involved the mechanical grinding of one surface of the disc utilising ascending grades of silicon carbide abrasive papers facilitated by adhering the specimens with super-glue to aluminium stubs compatible with the Alpha and Beta Grinder-Polisher.…”

Transient and residual stresses induced during the sintering of two dentin ceramics

“…Therefore the authors propose that the lower reported baseline quantification range of the mean of the maximum deflection for the IPS e.max ® Press specimens was predominantly the result of specimen polishing regime inducing a tensile stress state across the surface defect integral which accounted for the observed surface convexity. The grinding process was multidirectional owing to the rotational spect of the machine during grinding, such that machining induced cracks and residual stresses are difficult to asses so that the nature of the interaction between these opposing factors is unclear in the ceramic literature [38][39][40][41].…”