Glasses brittle fracture

Fig. 13. Transition between ductile fracture and brittle fracture when Al QFe Gd metallic glass is aimealed at 170°C.

The glass-fibre nylons have a resistance to creep at least three times as great as unfilled polymers. In the case of impact strength the situation is complex since unfilled nylons tend to break showing tough fracture whereas the filled polymers break with a brittle fracture. On the other hand the glass-filled polymers are less notch sensitive and in some tests and service conditions the glass-filled nylons may prove the more satisfactory. 

Equations 8.24 and 8.25 only apply to elastically brittle solids such as glass. However, many engineering materials only break in a truly brittle manner at very low temperature and above these temperatures failures are pseudo-brittle. These have many of the features of brittle fracture but include limited ductility. This plastic work can be included in the above equations, i.e. 

McKinney, Antonucci Rupp (1987) found that the clinical wear of the glass polyalkenoate cement compared favourably with that of the composite resin, but they noted that it was prone to brittle fracture and chemical erosion. 

Styrene polymers brittle fracture of, 23 363 burning of, 23 403 extrusion of, 23 398 glass-reinforced, 23 311 tensile strengths of, 23 359 Styrene product, factors in the quality of, 23 338-339 Styrene vapors, 23 403 Styrenic block copolymers, 24 102, 703-704... 

Adsorption-induced brittle fracture. This model is based on the hypothesis that adsorption of environmental species lowers the interatomic bond strength and the stress required for cleavage. This model of chemical adsorption can explain the fact that a certain alloy is susceptible to specific ions. An important factor in support of this mechanism is the existence of a critical potential below which the SCC does not occur in some systems, and this model underlines the relation between the potential value and the capacity of adsorption of the aggressive ion. It also explains the preventive action of SCC for some systems by cathodic protection. This model may interpret the rupture of plastic materials or glass. It is referred to as the stress-sorption model, and similar mechanisms have been proposed for HE and LME. In this model, the crack should propagate in a continuous way at a rate determined by the arrival of the embrittling species at the crack tip. The model does not explain how the crack maintains a sharp tip in a normally ductile material.156... 

MD has been used very effectively to elucidate vibrational spectra. Garofalini (1982) reported vibrational modes at 400, 800 and 1100 cm in vitreous Si02 compared to 450, 800 and 1050 cm observed in Raman and 465, 800 and 1100 cm observed in IR and 350, 800 and 1080 cm observed in inelastic neutron scattering. Experimental observation such as non-Newtonian behaviour of glass forming melts (Simmons et al., 1982), brittle fracture of Si02 (Ochoa et al., 1991) are only some of the other successful simulations using this powerful technique. 

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