Stress glasses

Stress birefringence The presence of stress in glass articles may be monitored readily since stressed glass is birefringent. Standard methods exist for these measurements. 

Elastic modulus Up to the fracture stress, glass behaves, for most practical purposes, as an elastic solid at ordinary temperatures. Most silicate-based commercial glasses display an elastic modulus of about 70GNm", i.e. about 1/3 the value for steel. If stress is applied at temperatures near the annealing range, then delayed elastic effects will be observed and viscous flow may lead to permanent deformation. 

Prince Rupert s drops provide an interesting and easily made example of the effects of stressing glass. 

Unfilled polypropylene generally is not recommended for use in load-bearing applications, because the plastic creeps rapidly even under moderate stresses. Glass-reinforced grades, however, can be used in high-load applications. Polypropylene also has good unnotched and excellent notched impact strength. Polypropylene s heat resistance is much superior to that of polyethylene. 

Figure 1 Schematic representation of the preparation of pressure densified and stressed glasses.

Plastics Type Unfilled Safe Stress Glass-filled ... 

To obtain further information about the stability of these stressed glasses, we will describe their dynamical properties in the last section. We will show that low frequency vibrational modes dominate the Sb-Te vibrational spectrum in agreement with its extremely easy recrystallisation under ambient conditions. This observation will be used to provide a way to improve the stability of the amorphous Ge-Te system by introducing high frequency modes and lowering the density of low frequency, floppy , modes thanks to proper doping. 

Type of stress Glass contraction greater than metal Glass contraction less than metal... 

Under ordinary application of a tensile stress, glass acts like a brittle solid. There is no observable plasticity unless the stress is highly concentrated in a localized region, such as when a microindenter is used. It may be shown that the strength brittle solid, i.e., the tensile stress required to separate two atoms a distance a apart initially, is given by... 

In a simple polariscope setup, light rays from a lamp are first allowed to pass through a polarizer whose sole function is to allow vibrations along only one plane. When an analyzer is oriented such that its plane of allowed vibrations is at 90° to that of the polarizer, all of the light intensity is cut off, leading to a field of view that is dark (i.e., the analyzer is crossed with respect to the polarizer to achieve extinction). A stressed glass specimen... 

Young s modulus Tensile fracture stress Shear fracture stress Glass transition temperature Ea = 3.05GPa (Taf = 82 MPa Taf = 58 MPa Tg = 120 °C... 

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