Ceramics material removal mechanisms

It is well known that the material removal mechanism in the grinding of ceramics is mainly a brittle fracturing process and grinding induced damage in terms of microcracks has been observed in various ceramics. Ceramic materials are very sensitive to cracks due to their low fracture toughness. The principal induced crack systems are the lateral cracks and the median cracks. The lateral cracks are parallel to the ground surface, and the median... 

Material Removal Mechanisms in Grinding of Ceramics and Glasses... 

Zhang, B. and Howes, T.D., Material-removal mechanisms in grinding ceramics. Annals ofCIRP, Vol. 43, no. 1,1994, pp. 305-308. 

A new model for material removal mechanism was proposed based on the experimental evidences. The "Double Fracture Model" was proved in the stock removal mechanism of ceramics lapping. 

However, suitable honing parameters and optimization approaches determined for metallic materials cannot be applied to the honing of ceramic materials caused by different material removal mechanisms specific for ceramics. Therefore, to supply the fundamental connections required for process optimization, the influence of honing conditions on the course and the result of the honing process must be defined for the various ceramic materials. 

Powder blasting, or abrasive jet machining, is a technique in which a particle jet (typically A1203 particles of 3-30 lm) is directed towards a target for mechanical material removal. It is a fast (typically, 500 pm depth in 20 minutes), inexpensive, and accurate directional etch technique for brittle materials like glass, silicon, and ceramics. For complex and small structures a mask can be used. 

The shapes depicted in Fig. 5.8a-c are typical for microholes obtained by drilling at high depth or, more generally, when melting is the dominant mechanism for material removal. These effects are not restricted to glass but are also observed in other materials such as ceramics [104]. 

Materials implanted into bone are modified by degradation and the action of different cell types. Degradation occurs by dissolution and the action of osteoclasts. Osteoclasts are very effective in material removal and provide a material resorption mechanism at the surface of the ceramic and particulate removal by phagacytosis (Heymann et al. 2001). Degradation of calcium phosphates as obtained from in vitro studies employing cells or animal studies has been discussed in several reviews (Frayssinet et al. 1993, Le Geros 1993, Heymann et al. 1999). 

The indentation fracture mechanics approach likens abrasive-workpiece interactions for grinding of ceramics to small-scale indentation events. The deformation and fracture patterns observed for normal contact with a Vickers pyramidal indentor under an applied load P are illustrated in Figure 3.1. A zone of plastic deformation is foimd directly imder the indentor. Two principal crack systems emanate from the plastic zone med-ian/radial and lateral cracks. Median/radial cracks are usually associated with strength degradation and lateral cracks with material removal. 

Most past research on grinding mechanisms for ceramics has followed either the indentation fracture mechanics" approach or machining" approach. The indentation fracture mechanics approach would seem to offer the possibility of describing both the material removal process and its influence on strength degradation in terms of the force or depth of cut at an... 

Kirchner, H.P. and Conway, J.C., 1985, Mechanisms of material removal and damage penetration during single point grinding of ceramics. Machining of Ceramic Materials and Components, ASME, New York, Vol. 17, pp. 53-61. 

These are some hypotheses combined with some evidences regarding this. More detailed research is necessary to elucidate the stock removal mechanism of brittle materials particularly in the case of different types of ceramics. 

The mechanism of material removal in abrasive machining of brittle ceramics has been well documented by Evans and Marshall who developed the lateral-crack chipping model. They demonstrated that material removal rate, AT caused by a passage of each grinding particle is related to the peak normal penetration forces, Fn, Vicker s hardness and fracture resistance as follows, ... 

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