Applied stress

The electromagnetic properties of steels depend on their composition, their microstructures and applied stresses. It is therefore natural to try to use magnetic and electrical parameters of steels to evaluate their microstructure. 

In the last section we considered tire mechanical behaviour of polymers in tire linear regime where tire response is proportional to tire applied stress or strain. This section deals witli tire nonlinear behaviour of polymers under large defonnation. Microscopically, tire transition into tire nonlinear regime is associated with a change of tire polymer stmcture under mechanical loading. 

A process involving combined corrosion and straining of the metal due to residual or applied stresses. The occurrence of stress corrosion cracking is highly specific only particular metal/environment systems will crack. 

During pressure sintering, interiDarticle compressive stress, approximated by the externally applied stress and nonnalized by the relative density of the compact p, supplements the surface tension driving force for pore shrinkage ... 

The measurement of mass using a quartz crystal microbalance is based on the piezoelectric effect.When a piezoelectric material, such as a quartz crystal, experiences a mechanical stress, it generates an electrical potential whose magnitude is proportional to the applied stress. Gonversely, when an alternating electrical field is... 

Of the adjustable parameters in the Eyring viscosity equation, kj is the most important. In Sec. 2.4 we discussed the desirability of having some sort of natural rate compared to which rates of shear could be described as large or small. This natural standard is provided by kj. The parameter kj entered our theory as the factor which described the frequency with which molecules passed from one equilibrium position to another in a flowing liquid. At this point we will find it more convenient to talk in terms of the period of this vibration rather than its frequency. We shall use r to symbolize this period and define it as the reciprocal of kj. In addition, we shall refer to this characteristic period as the relaxation time for the polymer. As its name implies, r measures the time over which the system relieves the applied stress by the relative slippage of the molecules past one another. In summary. 

Since the strain is the same in both elements in the Voigt model, the applied stress (subscript 0) must equal the sum of the opposing forces arising from the elastic and viscous response of the model ... 

The example shows that we have found an acceptable solution for 7(t) for the case of a periodic applied stress. Dividing through by Oq gives the appropriate compliance ... 

Other distinct classes of wood in a tree include the portion formed in the first 10—12 years of a tree s growth, ie, juvenile wood, and the reaction wood formed when a tree s growth is distorted by external forces. Juvenile fibers from softwoods are slightly shorter and the cell walls thinner than mature wood fibers. Reaction wood is of two types because the two classes of trees react differentiy to externally applied stresses. Tension wood forms in hardwoods and compression wood forms in softwoods. Compression wood forms on the side of the tree subjected to compression, eg, the underside of a leaning tmnk or branch. Tension wood forms on the upper or tension side. Whereas in compression wood, the tracheid cell wall is thickened until the lumen essentially disappears, in tension wood, tme fiber lumens are filled with a gel layer of hemiceUulose. 

Specific Surface. If a defined specific surface area is required, this can affect the choice of equipment. Machines that apply stress by cmshing generally create more ultrafines, and hence higher surface area, than impact mills. 

In recent years high compression roll mills have become commercially important. In contrast to traditional roU mills, these machines apply stress to a bed of material rather than to single particles (Fig. 7). By applying extremely high pressures to the roUs, ranging from 50 to 500 MPa (7,250—72,500 psi), fine particles can be produced. The end fineness depends on the cmshing pressure, and the output is determined by the roU speed. 

Gutting Mills. The machines applying stress by cutting are described in Figure 3e. They are usually employed for size reduction of ductile materials such as plastics, vegetables, and animal products. 

Fig. 7. Crack velocity as a function of the applied stress intensity, Kj. Water and other corrosive species reduce the Kj required to propagate a crack at a given velocity. Increasing concentrations of reactant species shifts curve upward. Regions I, II, and III are discussed in text.

For a single-value toughness material, dT/dc = 0. Accordingly, if the applied stress intensity factor is always increasing with crack length, equation 4 is always satisfied. Thus, the condition for fracture is equation 5, where is given by the applied loading conditions. 

FIG. 20-70 The influence of moisture as a percentage of sample saturation S on granule deformabihty. Here, deformation strain (AL/L) is measured as a function of applied stress, with the peak stress and strain denoted by tensile strength and critical strain (AL/L) of the material. Dicalcium phosphate with a 15 wt % binding solution of PVP/PVA Kolhdon VAG4. [Holm et al., Powder Tech., 43, 213 (1.9S.5J,] With land permission from Elsevier Science SA, Lausanne, Switzerland. 

Metals Successful applications of metals in high-temperature process service depend on an appreciation of certain engineering factors. The important alloys for service up to I,I00°C (2,000°F) are shown in Table 28-35. Among the most important properties are creep, rupture, and short-time strengths (see Figs. 28-23 and 28-24). Creep relates initially applied stress to rate of plastic flow. Stress... 

Stresses may be applied and/or residual. Examples of applied stresses are those arising from thermal expansion and contraction, pressure, and service loads. Applied stresses may be continuous or intermittent. Examples of residual stresses are those arising from welding, fabrication, and installation. The importance of residual stresses in SCC should not be underestimated. Residual stresses may... 

Residual. Stress-relief-anneal components and assemblies following cold working or welding operations. Note, however, that annealing has no effect on applied stresses. 

Applied. Generally, adequate reduction of applied stresses involves equipment redesign. 

Stress-relief-annealing cannot be expected to eliminate SCC in every case. Only residual stresses are reduced in stress-relief-annealing. Applied stresses, which may be responsible for the cracking, will remain. Inhibitors are not 100% effective in combating SCC. Complete coverage and inhibition is difficult to achieve, especially below deposits, in crevices, and in pits. 

Stresses from welding result principally from the effects of differential thermal expansion and contraction arising from the large temperature difference between the weld bead and the relatively cold adjacent base metal. Shrinkage of the weld metal during solidification can also induce high residual stresses. Unless these residual stresses are removed, they remain an intrinsic condition of the weldment apart from any applied stresses imposed as a result of equipment operation. 

Figure 15.19 shows various crack orientations that can occur in connection and attachment welds. Applied stresses from external loading of these components can add to the residual weld stresses, producing still higher stress loads. This can increase the susceptibility to stress-corrosion cracking and can affect orientation and location of crack paths. 

It was shown earlier that the NabaiTO-Hemirg model of creep in solids involved the migration of vacancies out of the stressed solid accompanied by counter-migration of atoms to reduce dre length of the solid in the direction of the applied stress. This property could clearly contribute to densification under an external pressure, given sufficient time of application of the stress... 

In an ideal fluid, the stresses are isotropic. There is no strength, so there are no shear stresses the normal stress and lateral stresses are equal and are identical to the pressure. On the other hand, a solid with strength can support shear stresses. However, when the applied stress greatly exceeds the yield stress of a solid, its behavior can be approximated by that of a fluid because the fractional deviations from stress isotropy are small. Under these conditions, the solid is considered to be hydrodynamic. In the absence of rate-dependent behavior such as viscous relaxation or heat conduction, the equation of state of an isotropic fluid or hydrodynamic solid can be expressed in terms of specific internal energy as a function of pressure and specific volume E(P, V). A familiar equation of state is that for an ideal gas... 

When a dislocation segment of length L is pinned at the ends under the influence of an applied shear stress t, a balance between the line tension and the applied stress produces a radius of curvature R given by [37]... 

The mechanical threshold stress determines the applied stress necessary for substantial thermal activation. The quantity = 7.0 eV for OFE... 

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