Material length change

Precise measurements of the dimensional stabiUty of low expansion materials indicate that vitreous siUcas, eg. Corning 7940 and Homosil, display a length change at 25°C of approximately 0.5 parts per biUion (ppb) per day (145). 

The gravity take-up must be used when handling hot materials in order to maintain chain and sprocket tooth engagement, as the chain length changes with thermal expansion. 

Temperature changes also cause dimensional changes in materials. When a material is heated or cooled, its length changes by an amount pro-... 

Several methods of measurement of the thermal expansion have been developed as a function of the material, dimension and shape of the sample, temperature range and requested accuracy. The measurement of the linear expansion coefficient a = 1/L (AL/A7) of a sample is done by recording the length change AL (in a definite direction) due to a temperature variation AT. 

There have been many investigations of photoinduced effects in -Si H films linked to material parameters. Changes have been observed in the carrier diffusion length, unpaired spin density, density of states in the gap, and infrared transmission. The transition from state A to B seems to be induced by any process that creates free carriers, including x-ray radiation and injection (double) from the electrodes. Because degradation in a solar cell is accentuated at the open-circuit voltage conditions, the A to B transition occurs upon recombination of excess free carriers in which the eneigy involved is less than the band gap. It has been pointed out that this transition is a relatively inefficient one and the increase in spin density takes place at a rate of 10-8 spins per absorbed photon. 

Extensometer for Testing High Explosive Materials. Proposed is a design for an extensometer to measure unit length changes upon compression or tension in i4x l-inch... 

Figure 9.40 shows another example of residual strain effects on the Raman spectrum. The Si stretching vibration changes its frequency when Si is in the form of a thin film on sapphire. We can compare the Raman band positions between the strain-free sample and strained sample to evaluate the bond length change, which can be converted to residual strain. The residual strain is commonly elastic in nature. Thus, the residual stress in materials can be determined with the linear elastic relationship between strain and stress. 

Once we have determined F, we may query a particular state of deformation as to the disposition of the vector dX as a result of the deformation. For example, the simplest question one might ask about the vector between two neighboring material particles is how its length changes under deformation. To compute the length change, we compute the difference... 

The strain tensor provides a more suitable geometric measure of relative displacements, and in the present context illustrates that the length change between neighboring material points is given by... 

The change in unit of length or volume that occurs due to a unit change in temperature. The expansion and contraction of a material with changes in temperature depend on its coefficient of linear thermal expansion, and movement of a part that is attached to another part with a lower CLTE value may be restricted. 

THERMAL EXPANSION - The change in length of a material with change in temperature. 

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