Permanent stress

In reality, around an inclusion embedded in a matrix a rather complex situation develops, consisting of areas of imperfect bonding, permanent stresses due to shrinkage, high stress-gradients or even stress-singularities, due to the geometry of the inclusions, voids, microcracks etc. 

If sufficient calcium hydroxide is present in the spraying drop, then the diffusion of sulfur dioxide is small. In liquid-sprayed fluidized beds the drops or films on the particles are under permanent stresses, and particle-particle impacts lead to constant destruction of the film surface. Thus, no converted calcium hydroxide reaches the film surface to perform the reaction for disposal, and consequently a strongly over-stoichiometric process is not necessary. 

Let us consider some definitions and their application to glass some aspects of transient or temporary stresses and of permanent stresses. 

The electrode configuration was stressed with a voltage impulse of nearly a sine-half-wave shape. This waveform was used to avoid thermal influence on the pollution layer that would occur on a permanently stressed sample. The leakage current was measured by a digital storage oscilloscope. 

The occurrence of permanent stress is thus related to glass solidification in the presence of temperature gradients. This change from viscous to rigid state takes place in the transformation or annealing range both are characterized by a similar... 

When this cooling rate is maintained, permanent stress in the plate does not exceed the value 1.5 MPa. 

The danger of temporary stress lies in the fact that too fast cooling may bring about fracture when the tensile strength of glass has been exceded. Permanent stress may lead to the same consequence in the final stage of temperature equalization. Badly distributed permanent stress, which always includes its tensile component, will reduce the final strength of the ware and thus impair its value. 

The cooling rate should preclude the formation of permanent stresses exceeding ]/20—l/40th of the glass tensile strength, i.e. approximately 1.5 —3,0 MPa which corresponds to an optical path difference of 50—lOO nm cm in birefringence measurements (see later). 

These considerations may be applied to both temporary and permanent stresses when assuming that permanent stress has the same value (with an opposite sign) as that which has been relieved by viscous flow at the onset of cooling. This principle serves as a basis for calculating safe annealing schedules. 

Below the lower annealing temperature, the rate of stress relief in glass is already so low that permanent stress can no longer occur. The glass can then be cooled at a three to six-fold rate. The same rates can also be employed for heating the ware to the annealing temperature. 

The response of the model indicates that as the stress is removed, the spring immediately recovers the deformation, but the dashpot deformation is permanent or recovers very slowly. This behavior is frequently seen in polymers subjected to a sudden and permanent stress that is later removed. 

One tie molecule is shown by the bold line passing through two crystalline lamellae. It is known that these tie molecules are fixed in the crystalline lamellae by short-chain branches of the comonomer molecules, meaning that they resist diffusing out of the lamellae under permanent stress [40-43, 56]. It is a unique... 

There is also an opportunity to use fibre ropes as tension textiles in buildings. An example is a bus station in Cambridge, UK (Fig. 13.25), erected in 1991. The structure was designed with four masts, each with a pair of forestays and back stays to support the 7-metre cantilevered roof. The stays are made of Parafil ropes with a Kevlar core their function is primarily to resist snow loading, but they are permanently stressed to... 

Since the brittle fibers are under a considerable stress which cannot relax, any surface flaw will cause a permanent stress concentration at its tip. When the local stresses exceed a certain hmit, crack growth and ultimately fracture will occur. 

Strain Point 510 C (950 F) 14.5 The point at which permanent stress is fixed in the glass product... 

Second fine annealing according to the rate cooling process, a certain temperature distribution is established in the blank until the solidification temperature is reached. It determines the permanent stress (cr) after annealing at room temperature ... 

The cooling rate in the solidification range is to be set in such a way that the permanent stresses are low enough to allow the machining of the blank. 

Any permanent stresses present should be so small that the casting is capable of withstanding rough machining. 

The permanent stress of the mirror blank was specified at the outer edge of the central hole and on all surfaces. The surface stresses were calculated with the help of finite-element models, which had been compared with the birefringence measurements. 

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