Glassy fracture

Bodies in which the physical properties are identical in all directions e.g., glass, air, water. This class of bodies includes all gases, most liquids, and the so - called amorphous solids such as glasses (that is, solids showing no external crystalline form, and breaking with a glassy fracture). Bodies of this type are called Isotropic Bodies. 

Effect of Structure on the Glassy Fracture of Highly Crosslinked Epoxies... 

The authors studied the glassy fracture behavior of the homologous series of DGEBA/DDS networks listed in Table 2. The fracture specimen employed was the double torsion test piece. Fracture data were collected over the temperature range Tg — 120 to Tg — 20 K, and all testing was performed at a single slow crosshead rate of 0.05 cm/min. This test rate was chosen because it minimized hysteretic effects and made all the networks fracture unstably over most of the temperatures investigated. 

Fig. 14. Stoichiometric DGEBA/DDS network fracture energy versus reduced test temperature, T, — T. Both rubbery and glassy fracture behavior are illustrated. Individual data points for glassy behavior are not plotted because of overlap. Rubbery fracture energies are from Fig 6, and glassy fracture energies are from Fig. 12 via Eq. (13) Epon 828/DDS O Epon lOOlF/DDS Epon 1(X)2F/DDS A Epon 1004F/DDS O Epon 1007F/DDS. (After LeMay >)...

To the authors knowledge, there have been no reports in the literature quantifying an dependence of the glassy fracture energy of thermosets. In fact, a number of studies indicate that such a simple dependence does not exist For example, epoxy networks with nearly equivalent M, have... 

The observed M dependence of arrest glassy fracture energies is curious because this is the same dependence predicted by Lake and Thomas for the threshold tearing of elastomers. It was previously shown that this dependence is exhibited by the rubber tear of the DGEBA/DDS epoxies over a wide range of temperatures, even though they were far removed from the threshold region. 

Glassy fracture coal, usually cubical in form. 

Glassy fracture energies of both network series showed an dependence when ductile yielding of the crack tip preceded crack propagation. Studies on the second series suggest that glassy fracture energies are closely proportional to Mci. 

Glassy fracture energies were measured using single edge notch (sen) and double torsion (DT) specimens (Figure 3). Rubbery fracture measurements above Tg en5)loyed only the SEN specimen. 

Figures 5 and 6 show the rubbery fracture energies of the two network series (Tg-T tesf O) The fractiu e energies increase with Mq throughout the range of temperatxires investigated. Apparently the topology differences in the Epon 828/MDA networks do not greatly affect the rubbery fracture. The glassy fracture energies (Tg-T test O) oT these networks, however, do not order with Mq.

Figure 5 Smooth (glassy) fracture surface of a brittle urea-formaldehyde adhesive layer fractured by stress developed in the adhesive layer as it cured. Note the tensile rupture of the cells at the wood surface (arrow) caused by the cure-shrinkage crack in the adhesive. 

All the SiC fibres are circular in cross-section with diameters of 15 p,m or less. The earliest SiC fibres, the Nicalon 100 series, showed all the fracture characteristics of a glassy structure, although TEM studies showed the presence of very small SiC grains of less than 2 nm as well as even smaller free carbon particles. The Nicalon 200 series became the standard fibre used for most ceramic matrix composites. The fibre has a diameter of 15 p.m and also shows a glassy fracture morphology, as Fig. 2 reveals. 

Cristobalite (alpha) [14464-46-1] [Named after Cerro San Cristdbal near Pachuca, Mexico] (ICSD 47219 and PDF 39-1425) SiO, M = 60.0843 46.74 wt.% Si 53.26 wt.%0 (Tectosilicates, framework) Coordinence Si (4) Tetragonal as 497.1 pm cs 691.8pm (Zs4) P.G. 422 S.G. P4,2,2 Uniaxial (-) e= 1.482 0)= 1.489 S= 0.007 6-7 2330 Habit coarse aggregate. Color colorless. Streak white. Diaphaneity transparent to translucent. Luster vitreous( Le., glassy). Fracture conchoidaL Twinning (III). Oiemical resistant to Strong mineral acids, attacked by HF and molten alkali-metal hydroxides. Mdting point 1713 C... 

Those ceramics that have been fired at a higher temperature fuse completely into a solid impervious mass having a glass-like surface and showing the same glassy fracture when broken. Only those adhesives capable of forming a chemical bond with these surfaces... 

---