Stress-induced frequency shifts

Expressions for the stress-induced frequency shifts for an A, mode of a trigonal center. Intensity ratios of the stress-split components for different polarizations of absorbed light are also given. [From Kaplyanskii (1964)]... 

Many connections have been established between microscopic MD simulations and macroscopic experimental properties of polymers, such as seen in conformational disorder and heat capacities [1], molecular motion and the vibrational spectrum- [2], stress-induced frequency shifts and conformational changes [3], twist motion and the dielectric a-relaxation [4], molecular diffusion... 

As we have seen, the changes to a vibrational spectrum as orientation is induced are ones of intensity. Application of stress is well known to induce frequency shifts. However, both effects only subtly change a well developed spectrum characteristic of the specimen itself. One obvious way to study these subtle changes is to apply force sinusoidally and to discriminate electronically between the DC component of the signal (the invariant) and the AC (that of interest). Further, in several practical situations polymers are regularly subjected to variable loads, and their behaviour under these situations is critical. In addition, their deformations under quasi-static stresses are very different from those under alternating ones. 

The behavior of the Raman spectrum under stress of the stretching vibration of the B—H complex has been reported recently by Stutzmann and Herrero (1988a,b) and by Herrero and Stutzmann (1988a,b). Spectra measured at 100 K are shown in Fig. 18 for several values of [100] stress. The dependence of the mode frequency on [100] and [112] stress is shown in Fig. 19. There were stress induced splittings observed for [100], [112], and [110] stress directions. For the [111] stress direction the line broadened for low stresses but did not split. Further, the stress-split component that shifts upward in frequency as the stress is increased decreases in intensity. 

Ultrasonic Pressure Transducers. Advantage is taken of the fact that pressure influences sound propagation in solids, liquids, and gases, but in different ways. In solids, applied pressure leads to so-called stress-induced anisotropy, In liquids, the effects of pressure are usually small (relative to effects in gases), but the frequency of relaxation peaks can be shifted significantly,... 

An extensive study of the line width of v(3SCl) in paradichlorobenzene containing various impurities was done by Kojima et al. 25). The results are interpreted as an effect of the volume difference VA - VB and of the stresses and strains induced by the impurities. No overall frequency shift was reported by these authors. 

Cerdeira F, Buchenauer CJ, Poliak FH, Cardona M (1972) Stress-induced shifts of first-order Raman frequencies of diamond- and zinc-blende-type semiconductors. Phys Rev B 5 580-593... 

Assume that the sample does not consist of planar layers, but instead of a sand pile, a froth, an AFM tip, an assembly of spheres or vesicles, a cell culture, a droplet, or any other kind of heterogeneous material. There are many interesting samples of this kind. The frequency shift induced by such objects can be estimated from the average ratio of stress and speed at the crystal-sample interface. The latter is the load impedance of the sample. The concept of the load impedance tremendously broadens the range of applicability of the QCM. The load impedance is the conceptual link between the QCM and complex samples. If we want to predict the frequency shift induced by a complex sample, we must ask for the average stress-speed ratio. If this ratio can be estimated in one way or another, a quantitative analysis of the experimental QCM data is in reach. Otherwise, the analysis must remain qualitative. 

It is worth considering why there is a stress- or strain-induced peak frequency shift for these tends in carbon fibres. It would seem... 

K Tashiro, G Wu, M Kobayashi. Morphological effect on the Raman frequency shift induced by tensile stress applied to crystalline polyoxymethylene and polyethylene Spectroscopic support for the idea of an inhomogeneous stress distribution in polymer material. Polymer 29 1768-1783, 1988. 

The adsorbate induced compressive surface stress was however demonstrated to be relevant for the O/Ni(100) system because it explains also other findings i) the observed frequency shift depends on the order state of the adsorbate and is smaller when the oxygen is adsorbed disorderly [85Roc], an effect that would not be expected if the adsorbate affects only the surface force constants between the substrate atoms ii) Ni(lOO) reconstructs with clockwise and anti-clockwise rotations of the substrate atoms around the adsorbate when the latter is C or N instead of O or S. The displacement pattern of such p4g... 

For a HIPS sample tested at a stress amplitude of 17.2 MPa and a frequency of 0.2 Hz, hysteresis loops taken at various cycles (Fig. 7) indicated that craze initiation was first observed for this sample after about 20 cycles, while 283 cycles were required to fracture. For similar fatigue tests carried out at the lower frequency of 0.02 Hz, the cycles to fracture were decreased (from 283 to 64) and loop asymmetry and craze formation began sooner, at about 1-2 cycles. The changes produced in hysteresis loops with cycling are shown in Fig. 19. With decrease of test frequency reduces, the entire S-N curve shifts to the left as shown by Fig. 18, and, because of the increased time for each cycle, fatigue induced craze initiation occurs earlier in the specimen lifetime. 

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