Straining stress, external

Figure 2. Surface of the HIPS fracture treated by the solvent vapors while applying the external straining stress, increase X3500...

In conclusion it can be said that the heating with linear temperature rise, accompanied by application of external strain stresses strongly influences the nature of structural rearrangements in the investigated xmciystallized PET filaments. The observed fibers net deformation at tensile stress values less than 0.7 MPa and more than 1.2 MPa can be explained with a faster crystallization of the amorphous PET bimdle from rubbery state, as a consequence of the influence of the applied tensile stress. The fluid-like deformation process predominates when the ap>plied stresses are from 0.7 MPa to 1.2 MPa. It was found that after heating up to 200 C amorphous PET filaments could preserve the amorphous state when the applied external strain stresses are in the same range. 

We will confine ourselves to those applications concerned with chemical analysis, although the Raman microprobe also enables the stress and strain imposed in a sample to be examined. Externally applied stress-induced changes in intramolecular distances of the lattice structures are reflected in changes in the Raman spectrum, so that the technique may be used, for example, to study the local stresses and strains in polymer fibre and ceramic fibre composite materials. 

FIGURE 9.2 EPR powder pattern of the [2Fe-2S]1+ cluster in spinach ferredoxin. Trace A shows an attempt to fit the spectrum with the diagonal linewidth Equation 9.1. In trace B the spectrum is fitted with the nondiagonal g-strain Equation 9.18. Trace C shows an experiment in which the spectral features are slightly shifted (solid trace) under the influence of an external hydrostatic stress. (Data replotted from Hagen and Albracht 1982.)... 

The analysis of propagating acoustic waves in an elastic medium allows its characterization by means of strain-stress relationships. The stress ay is defined as the ratio of an external force F parallel to a direction i (x,y or z) to a surface S perpendicular to the direction j. 

Although PBT fiber also has a plateau region in the stress-strain curve [4], the crystalline chains do not respond to external strain in the first few percent of deformation. They increased in length only when the strain is above 4% (see Figure 11.13). Therefore, initial macroscopic deformation involved viscous flow of the amorphous phase. Furthermore, PBT undergoes strain-induced crystal transformation at moderately low strains of 15-20% [75], The differences in their microscopic crystalline chain deformation explained why PTT has a better elastic recovery than PBT even though both have contracted chains and knees in their stress-strain curves [4, 69],... 

Anastassakis and M. Cardona, Phonons, Strains, and Pressure in Semiconductors F. H. Poliak, Effects of External Uniaxial Stress on the Optical Properties of Semiconductors and Semiconductor Microstructures... 

An externally applied stress will affect the internal strain and the domain structures will respond this process is termed the ferroelastic effect. Compression will favour polar orientations perpendicular to the stress while tension will favour a parallel orientation. Thus the polarity conferred by a field through 90° domain changes can be reversed by a compressive stress in the field direction. Stress will not affect 180° domains except in so far as their behaviour may be coupled with other domain changes. 

For analyzing the fracture behavior of filler clusters in strained rubbers, it is necessary to estimate the strain of the clusters in dependence of the external strain of the samples. In the case of small strains, considered above, both strain amplitudes in spatial direction n are equal (t A F i). because the stress is transmitted directly between neighboring clusters of the filler network. For strain amplitudes larger than about 1%, this is no longer the case, since a gel-sol transition of the filler network takes place with increasing strain [57, 154] and the stress of the filler clusters is transmitted by the rubber matrix. At larger strains, the local strain eAtfl of a filler cluster in a strained rubber matrix can be determined with respect to the external strain if a stress equilibrium between the strained cluster and the rubber matrix is assumed ea GpX =6rm( u)) With Eq. (29) this implies... 

A comparison of Eqs. (31) and (32) makes clear that for large deformations, when the stress of the clusters is transmitted by the rubber matrix, the strain eAj/i of the clusters increases faster with their size than the failure strain eFjU. Accordingly, with increasing strain the large clusters in the system break first followed by the smaller ones. The maximum size of clusters surviving at exposed external strain eu is estimated by the stress equilibrium between the rubber matrix and the failure stress oF F(UGA( (U) of the clusters ... 

An external pressure (stress) that is exerted on a material will cause its thickness to decrease. A shear stress is applied parallel to the surface of a material, and may cause the sliding of atomic layers over one another. The resultant deformation in the size/shape of the material is referred to as strain, related to the bonding scheme of the atoms comprising the solid. For example, a rubbery material will exhibit a greater strain than a covalently bound solid such as diamond. Since steels contain similar atoms, most will behave similarly as a result of an applied stress. If a stress causes a material to bend, the resultant flex is referred to as shear strain. For small shear stresses, steel deforms elastically, involving no permanent displacement of atoms. The deformation vanishes when shear stress is removed. However, for a large shear stress, steel will deform plastically, involving the permanent displacement of atoms, known as slip. 

The internal stress in plasma polymer films is generally expansive, i.e., the force to expand the film is strained by external compressive stress. According to the concept presented by Yasuda et al. [1], the internal stress in a plasma polymer stems on the fundamental growth mechanisms of plasma polymer formation. A plasma polymer is formed by consecutive insertion of reactive species, which can be viewed as a wedging process. The internal stress is related to how frequently the insertion occurs as well as on the size of inserting species. The both factors are dependent on the operational factors of plasma polymerization. 

In order to comprehend the adhesion properties of piliated bacteria, it is necessary to acquire detailed information not only about the biophysical properties of individual pili under various conditions, in particular their behavior in regions II and III, but also the adhesin on the tip of the pilus. Moreover, to understand the unfolding and refolding properties of the pilus rod a good knowledge about the properties of individual bonds exposed to strain/stress is needed. A full understanding of adhesion properties of piliated bacteria requires finally knowledge about how several pili cooperate to deal with an external force. 

If we take a value of Ha — 30 MPa (Martmez-Salazar et al, 1988) for the amorphous phase of i-PP and solve eqs. (4.15) and (4.16), values of // = 143 MPa and He = 119 MPa are obtained. The former value of 143 MPa fits well with the ab initio calculation for the a phase (Balta Calleja et al, 1988). In conclusion, the determination of microhardness is shown to be a technique capable of detecting polymorphic changes in polymers. Further examples of polymorphic crystal-crystal transitions induced by external field (stress or strain) are given in Chapter 6. 

Besides the outstanding chemical characteristics of certain mesoscopic structures, they also possess a number of surprising physical characteristics. Typical examples are the initiation of premelting near dislocations, twin boundaries or grain boundaries (e g. Raterron et al. 1999, Jamnik and Maier 1997) and the movement of twin boundaries under external stress which leads to non-linear strain-stress relationships. It is the purpose of this review to focus on some of the characteristic features of mesocopic structures and to illustrate the generic results for the case of ferroeleastic twin patterns (Salje 1993). 

Pure torsion tests were performed on ice single crystals at a constant imposed external shear stress". Softening was evidenced as the creep curves revealed a strain-rate increase, up to a cumulated plastic strain of 7%, see figure 1. Note that such a behaviour was also observed during compression and tension tests. ... 

An extension of rubber elasticity (i.e. of the description of large, static and incompressible deformations) to nematic elastomers has been given in a large number of papers [52, 61-66]. Abrupt transitions between different orientations of the director under external mechanical stress have been predicted in a model without spatial nonuniformities in the strain field [52,63]. The effect of electric fields on rubber elasticity of nematics has been incorporated [65]. Finally the approach of rubber elasticity was also applied recently to smectic A [67] and to smectic C [68] elastomers. Comparisons with experiments on smectic elastomers do not appear to exist at this time. Recently a rather detailed review of the model of an-... 

The activation volumes, normalized by b, predicted by the models using eqs. (9.30) are compared in Fig. 9.23 with some of those measured by Kazmierczak et al. (2005) in strain-rate-jump experiments. In the model calculation for the nucleation of the monolithic-screw-dislocation emission A = 20 nm X/b = 78.5) was used. The data for 13 up-jump strain-rate-change experiments are also plotted in Fig. 9.23. The details of these experiments are given by Kazmierczak et al. (2005). The measured Av /Z> for the jump experiments from s = 5.5 X 10 to 5.5 X 10 fall quite close to the models for nucleation of dislocation half loops. The data for jumps at considerably lower strain rates and smaller flow stresses fall a bit closer to the model of nucleation of monolithic screw dislocations but are in much less satisfactory agreement. In all cases it was assumed that the externally applied stresses directly apply locally, which is the assumption in the Sachs model. However, considering the generally confused morphology of... 

In Fig. 12.6(b), at higher levels of externally applied stress, the plastic zone is now of extent C < D — a), i.e., it is still smaller than the unaffected ligament. This range of pervasiveness of plasticity in the part is called contained yielding. Depending on the type of constitutive plastic response of the material, the distributions of stress and strain both inside and outside the plastic zone are now quite different from those of SSY. 

Finally, in Fig. 12.6(c) the external applied stresses are larger still and the plastic zone has now increased over the entire cross section where > D — a). Here the entire part response is importantly altered by the plasticity of the material and the nature of its strain-hardening behavior. 

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