Glass internal stresses

Theory of the fictitious temperature field allows us to analyze the problems of residual stresses in glass using the mathematical apparatus of thermoelasticity. In this part we formulate the boundary-value problem for determining the internal stresses. We will Lheretore start from the Duhamel-Neuinan relations... 

Corrosion attack on the polymer is influenced by permeation rate, as weU as internal stresses or fatigue, that distorts or fractures the resin glass fiber... 

Two other temperatures are important in the working of glass. At the annealing point (p = 10 poise) there is still enough fluidity to relax internal stresses in about... 

Glass transition temperature (Tg), measured by means of dynamic mechanical analysis (DMA) of E-plastomers has been measured in binary blends of iPP and E-plastomer. These studies indicate some depression in the Tg in the binary, but incompatible, blends compared to the Tg of the corresponding neat E-plastomer. This is attributed to thermally induced internal stress resulting from differential volume contraction of the two phases during cooling from the melt. The temperature dependence of the specific volume of the blend components was determined by PVT measurement of temperatures between 30°C and 270°C and extrapolated to the elastomer Tg at —50°C. 

Strain point Highest temperature from which the glass can be rapidly cooled without serious internal stress 1014 5 820 470... 

Rice R. W., 1979, Internal stress dependence of the hardness of crystallized glasses, J. Mater. Sci., 14, 2768-2772. 

Glasses, like most ceramics, are susceptible to fracturing under stresses caused by temperature gradients. Internal stresses in a material arise when there are different temperature changes in adjacent regions. In the absence of stress, a temperature change causes afractional dimensional change, AL/L = e = a AT. Under stress, the total strain is... 

Flexibilizers generally cannot be used to counteract internal stress in high temperature adhesive because of their relatively low glass transition temperature and thermal endurance properties. However, most high-temperature adhesive systems incorporate metallic fillers (generally aluminum powder) to reduce the coefficient of thermal expansion and degree of shrinkage. 

Metal fillers for high-temperature adhesives must be carefully selected because of their possible effect on oxidation, as indicated in the previous section. Carrier films, such as glass cloth, are generally used to facilitate the application of the adhesive, but they also provide a degree of reinforcement and lowering of the coefficient of thermal expansion. Thus, they reduce the degree of internal stress experienced at the joint s interface. 

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