Papers by Keyword: Median crack

Abstract: Surface degradation and cracking of dense hydroxyapatite were evaluated through Vickers micro indentation using indentation loads ranged from 25 gf to 2000 gf. Crack lengths, imprint diameters and the number of lateral cracks and chips were measured using SEM. The crack length-indentation load data were analyzed with regard to the specific relations of Palmqvist and fully developed radial cracks. Crack type transition load from Palmqvist to median crack was experimentally assessed through serial sectioning technique. The analytical estimated transition load, based on the theoretical relation of the indentation load and crack lengths showed a good agreement with one obtained from experimental itinerary. Palmqvist and median cracks were identified in low and medium indentation loads, respectively. High indentation load could also lead to the formation of lateral cracks and chips. The tendency for lateral cracking was evaluated taking into account the number of lateral cracks and chips. The chips were found to be appeared just after test in higher indentation load, whereas in medium loads they could be detectable only after several weeks.

Abstract: A new non-destructive method was developed to identify the grinding mode of silicon wafers, which is based on the information of subsurface cracks extracted from the surface topography of the ground silicon wafers measured with a 3D surface profiler. We examined extensive measurement data of the surface topography of silicon wafers processed by single grain grinding or real grinding operation, and our results show that the information about median cracks could be captured if the lateral sampling interval of the 3D surface profiler is small enough, even if the grain depth of cut is below 20nm. If the maximum valley of the measured surface topography is approximately equal to the grain depth of cut, surface formation will be under ductile mode, whereas, if the maximum valley is several times larger than the grain depth of cut, surface formation will be under brittle mode. According to this criterion, silicon wafers ground by ductile mode or brittle mode could be identified rapidly and conveniently. Experimental validation shows that this method is accurate.

Abstract: Four kinds of brittle materials were used to evaluate the bending strength under three-point bending and the characteristics of the elastic wave signal by Vickers indentation. The bending test was carried out under room temperature and high temperature. A crack was made at the tension side of the specimen with a Vickers indenter to investigate fracture strength. Fracture wave detector was used to evaluate characteristics of waveform and frequency of the elastic wave signal.