Dilation thermal

In eq. (5.28) /g is the critical free-volume fraction at Tg and a is the volumetric (dilatational) thermal coefficient of expansion of the sub-cooled liquid. Then, the shift factor discussed in Section 5.3.1 is... 

These values are considered as the universal WLF constants, giving the widest range of agreement over many prominent amorphous polymers. From these choices one calculates that the free-volume fraction /g at the glass-transition temperature is 0.025 and the dilatational thermal coefficient of expansion of a sub-cooled polymer melt at the glass-transition temperature is a = 2.8 x 10 ... 

The lack of thermal stability of EuB and YbB5 results from the high volatility of the metals and the great dilatation of the unit cell and, consequently, the fragility of the B—B bonds. The exceptional volatility of Yb explains why YbB is less stable than LaB, although their unit cells have nearly the same size. 

In order to reproduce the temperature variation of the lattice constants, the anisotropy of the lattice expansion has to be taken into account. For this purpose, the tensor of thermal expansion ot is introduced instead of the scalar a , and the tensor of deformation due to the HS <- LS transition is employed instead of the dilation (Fh — Fl)/Fl. Each lattice vector x T) can now be... 

Mechanical properties of the sample In the simplest case, the sample stands alone (it is fixed by a screw as in measure of Section 11.5.2), or a support may be necessary as in the examples of Section 11.3.2 and Section 11.4.2. In the latter case, the support represents again a thermal conductance in parallel with the sample. Such shunt conductance must be taken into account for low-conductance samples. Contractions (or dilatations, see Chapter 13), which take place when the sample is cooled, not only change the geometrical factor, but also influence the mechanical joints and hence the thermal contact resistance. Various mechanical solutions, some of them very exotic , have been used in the measure of the thermal conductivity [2-4]. 

MSE.13. I. Prigogine et J. Philippot, Sur la theorie moleculaire de I helium hquide, II. Le coefficient de dilatation thermique de I hehum liquide (Molecular theory of liquid hehum, II. The coefficient of thermal dilatation of hquid hehum), Physica 19, 227—234 (1953). 

The magnet temperature variation AT is approximately proportional to the power dissipated by the magnet and therefore to the square of the magnet current I. The variation of AS is a function of AT which reflects the changes in magnet geometry due to thermal dilatations. The net result is... 

From a thermal standpoint, cosmic history can be summed up as a generalised cooling trend induced by the dilatation of space. However, here and there, in certain regions, stars concentrate and bear matter to high temperatures, as balls of incandescent material floating in a cold ocean. 

The second noteworthy morphological feature is presented in Fig. 12b. This micrograph depicts the pre-crack front of 15-1500-70F, which had a value significantly above that of the control, as shown in Fig. 11 a. The holes may be examples of the dilatation effect observed in CTBN-modified epoxies l9,22> in which rubber particles dilate in mutually perpendicular directions under the application of a triaxial stress and then collapse into spherical cavities following fracture. Dilatation requires a mismatch in coefficients of thermal expansion of resin and rubber 11. This effect will therefore be most striking when the elastomeric phase is homogeneous, as is apparently the case here. 

In analogy with the approach that has been described in the section on the low-temperature heat capacity, the high-temperature heat capacity of the LnXj compounds can be described as the sum of the lattice and excess contributions (eq. (1)). However, whereas at low temperature the lattice heat capacity mainly arises from harmonic vibrations, at high temperatures the effects of anharmonicity of the vibrations, of thermal dilation of the lattice and of thermally... 

The volume decrease accompanying formation of intermetallic compounds produces a bulk dilation stress over the whole thickness of growing layers. Thermal expansion of the couple constituents during heating up as well as their contraction during cooling down in the course of successive anneals of the same couple produces a shear stress. These inevitably lead to the rupture of Ni-Zn and Co-Zn diffusion couples, with the latter effect being most disastrous. 

The interpretation of dilatometric volume measurements is complicated by the fact that the molten fat has a coefficient of thermal expansion (about 0.00084 mL/gK) more than twice that of solid fat (about 0.00038 mL/gK). This difference means that the melting dilation is temperature-dependent (Stauffer, 1996). In principle, this could be allowed for by measuring the specific volume of both the fully molten fat and the fully solid fat at the measurement temperature. However, while the specific volume of the molten fat is easily measured using the dilatometer, that of the solid fat is not. This difficulty is circumvented by assuming, by convention, that the temperature dependence of specific volume is the same for both the molten fat and the solid fat (thus making the melting dilation temperature independent), and that the melting dilation itself has a constant value, independent of fat type, of 0.1 mL/ g (= 0.1 L/kg). Thus (Hannewijk et al., 1964),... 

Key factors of SCC. The stress applied on a metal is nominally static or slowly increasing tensile stress. The stresses can be applied externally, but residual stresses often cause SCC failures. Internal stresses in a metal can be due to cold work or a heat treatment. In fact, all manufacturing processes create some internal stresses. Stresses introduced by cold work arise from processes such as lamination, bending, machining, rectification, drawing, drift, and riveting. Stresses introduced by thermal treatments are due to the dilation and contraction of metal or indirectly by the modification of the microstructure of the material. Welded steels contain residual stresses near the yield point. Corrosion products have been shown to be another source of stress and can cause a wedging action. 

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