Glass shear effects

Mechanical cell disruption techniques are based on high shear effects as fluid is forced through a narrow orifice, or a chamber containing rotating disks and glass beads to break up the cellular material. Both techniques enable some control over the extent of cell disruption. 

We have already discussed confinement effects in the channel flow of colloidal glasses. Such effects are also seen in hard-sphere colloidal crystals sheared between parallel plates. Cohen et al. [103] found that when the plate separation was smaller than 11 particle diameters, commensurability effects became dominant, with the emergence of new crystalline orderings. In particular, the colloids organise into z-buckled" layers which show up in xy slices as one, two or three particle strips separated by fluid bands see Fig. 15. By comparing osmotic pressure and viscous stresses in the different particle configurations, tlie cross-over from buckled to non-buckled states could be accurately predicted. 

Fig. 2. Effect of temperature on the shear modulus of dry nylon-6,6 (—) and nylon-6,6 plus 30% glass fiber (-). To covert MPa to psi, multiply by 145.

Net-tension failures can be avoided or delayed by increased joint flexibility to spread the load transfer over several lines of bolts. Composite materials are generally more brittle than conventional metals, so loads are not easily redistributed around a stress concentration such as a bolt hole. Simultaneously, shear-lag effects caused by discontinuous fibers lead to difficult design problems around bolt holes. A possible solution is to put a relatively ductile composite material such as S-glass-epoxy in a strip of several times the bolt diameter in line with the bolt rows. This approach is called the softening-strip concept, and was addressed in Section 6.4. 

Prati, C., Nucci, C. Montanari, G. (1989). Effects of acid and cleansing agents on shear bond strength and marginal microleakage of glass-ionomer cements. Dental Materials, 5, 260-5. 

In the above, the variable R is the radius between center to center fiber spacing, while r is the fiber radius. The shear modulus (Gm) can be approximated as Em/3. The matrix modulus is effected by the level of crystallinity and it is important that the samples are fully crystallized to ensure reproducibility. The value of (> for 30wt% glass-fiber-reinforced PET has been calculated as 3.15 x 104. Using the mathematical analysis shown above, the orientation function of the glass fiber... 

Barsoum, M. and Tung, F.C. (1991). Effect of oxidation on single fiber interfacial shear stresses in a SiC--borosilicate glass system. J. Am. Ceram. Soc. 74, 2693-2696. 

Cheng, T.H., Jones, F.R. and Wang, D. (1993). Effect of fiber conditioning on the intcrfacial shear strength of glass-fiber composites. Composites Sci. Technoi. 48, 89 96. 

Fig. 6.12. Toughness maps depicting contours of predicted fracture toughness (solid lines in kJ/m ) for (a) glass-epoxy composites as a function of fiber strength, Uf, and frictional shear stress, tf and (b) Kevlar-cpoxy composites as a function of at and clastic modulus of fiber, Ef. The dashed line and arrows in (a) indicate a change in dominant failure mechanisms from post-debonding friction, Rif, to interfacial debonding, Sj, and the effect of moisture on the changes of Of and Tf, respectively. Bundle debond length...

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