Stress-Optical Behavior

Because these materials stress-soften on extension, their stress-optical behavior depends upon strain level and degree of prestrain (Estes et a/., 1969,1970 Koutsky et a/., 1970). The classical equation for the stress-optical coefficient (SOC) derived from the theory of photoelasticity (Treloar, 1958) is not obeyed  

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The wavelength dispersion of orientation birefringence must be controlled precisely for color display. Based on the Kuhn and Griin model proposed for the stress-optical behavior of cross-linked rubbers, the orientation birefringence Anin(l] of an oriented polymer is expressed as follows [20, 23-27] ... 

Llorente, M. A. Mark, J. E. Saiz, E., Stress-Optical Behavior of Polydimethylsilmethylene [-SiCCHjl CH -], a Hydrocarbon Analog of Polydimethylsilox-ane, and a Silicon Analogue of Polyisobutylene. J. Polym. Sci., Polym. Phys. Ed. 1983, 21,1173-1185. 

Kroger, M., Luap, C., and Muller, R. (1997) Polymer melts under uniaxial elongational flow stress-optical behavior from experiments and NEMD computer... 

This stress-strain behavior is consistent with the optic metallographic data which evidenced partial redistribution of hydrogen over the powder particles when the compacting temperature was increased to 400°C and uniform hydrogen distribution on additional annealing or during plastic deformation at T > 500°C. 

The photoelastic behavior of nonionized PAAm network and ionized P(AAm/MNa) network prepared by the copolymerization of AAm with MNa ( MNa = 0.05) was investigated in water-acetone mixtures [31]. For a pure PAAm network, the dependences of all photoelastic functions (see Eqs. (15) and (16)), i.e. modulus G, strain-optical function A and stress-optical coefficient C, on the acetone concentration in the mixtures are continuous (Fig. 17). At ac = 54 vol %, the ionized network undergoes a transition which gives rise to jumpwise change in G, A and C also the refractive index of the gel n8 changes discontinuously. While in the collapsed state the optical functions A and C are negative, in the expanded state they are positive. 

As shown in Fig. 9, the stress relaxation curves of all AEC/AA solutions collapse into one curve when the solutions were presheared with the same rate. Because the stress relaxation is at the molecular level and the chiro-optical properties reflect the suprastructural level, it is expected that the lyotropic solutions with different chiro-optical properties have the same stress relaxation behavior in both the tumbling and flow-align regions. 

This chapter is the first in a series that will make the case that many of the important features of real materials are dictated in large measure by the presence of defects. Whether one s interest is the electronic and optical behavior of semiconductors or the creep resistance of alloys at high temperatures, it is largely the nature of the defects that populate the material that will determine both its subsequent temporal evolution and response to external stimuli of all sorts (e.g. stresses, electric fields, etc.). Eor the most part, we will not undertake an analysis of the widespread electronic implications of such defects. Rather, our primary charter will be to investigate the ways in which point, tine and wall defects impact the thermomechanical properties of materials. 

Dynamic birefringence techniques have been developed by Stein et al. (66), Read (54), Yamada and Hayashi (85) and Hopkins (25). By this technique the stress, strain and birefringence are measured simultaneously while the applied strain varies. By making such measurements as a function of frequency and temperature one can in principle separate the time dependencies of orientation of molecular response in a multiphase system as well as correlate the optical behavior with the mechanical spectrum. This technique can be correlated for example with the dynamic X-ray technique allowing separation of the amorphous and crystalline behavior. 

A dilute polymer solution is a system where polymer molecules are dispersed among solvent molecules. An assumption common to any existing theory for flow properties of polymer solutions is that the structure of solvent molecules is neglected and the solvent is assumed to be replaced by a continuous medium of a Newtonian nature. Thus, macroscopic hydrodynamics may be used to describe the motion of the solvent. Recently, some ordering or local structure of solvent molecules around a polymer chain has been postulated as an explanation of the stress-optical coefficient of swollen polymer networks (31,32) so that the assumption of a solvent continuum may not apply. The high frequency behavior shown in Chapter 4 could possibly due to such a microscopic structure of the solvent molecules. Anyway, the assumption of the continuum is employed in every current theory capable of explicit predictions of viscoelastic properties. In the theories of Kirkwood or... 

Since there are very few dynamic experimental investigations of pretransitional effects [8], not much modeling has been reported to date either. Based on work for the macroscopic dynamics of the nematic-isotropic transition in sidechain polymers [27 -29], it has been suggested [28] that the non-meanfield exponent observed in dynamic stress-optical experiments [8] can be accounted for at least qualitatively by the mode-coupling model [28, 29]. Intuitively this qualitatively new dynamic behavior can be traced back to static nonlinear coupling terms between the nematic order parameter and the strain tensor. 

Birefringence can be used to characterize non-Gaussian behavior in PDMS bimodal elastomers. - A large decrease the stress-optical coefficient (ratio of birefringence to stress) was observed over a relatively small range in elongation, presumably due to limited extensibility of the short chains. 

In Chapter I the basic concepts of testing are discussed along with the purpose of specifications and standards. Also discussed is the basic specification format and classification system. The subsequent chapters deal with the testing of five basic properties mechanical, thermal, electrical, weathering, and optical properties of plastics. The chapter on mechanical properties discusses in detail the basic stress-strain behavior of the plastic materials so that a clear understanding of testing procedures is obtained. Chapter 7 on... 

Figure 13.15 shows the birefringence behavior of SPS against the applied stress during the melt extrusion. From the slope, the stress-optical coefficient is calculated to be -9.6 x l(F Pa. Tlie study of the dynamic viscoelasticity and the dynamic birefringence measurements demonstrated that a similar value (-9.5 x KUPa ) is obtained for the stress-optical coefficient of SPS, and this value is almost twice as much of that of APS (-4.7 x l(F Pa ) obtained by the same measurements [13]. 

Cathodoluminescence microscopy and spectroscopy techniques are powerful tools for analyzing the spatial uniformity of stresses in mismatched heterostructures, such as GaAs/Si and GaAs/InP. The stresses in such systems are due to the difference in thermal expansion coefficients between the epitaxial layer and the substrate. The presence of stress in the epitaxial layer leads to the modification of the band structure, and thus affects its electronic properties it also can cause the migration of dislocations, which may lead to the degradation of optoelectronic devices based on such mismatched heterostructures. This application employs low-temperature (preferably liquid-helium) CL microscopy and spectroscopy in conjunction with the known behavior of the optical transitions in the presence of stress to analyze the spatial uniformity of stress in GaAs epitaxial layers. This analysis can reveal,... 

In order to supplement micro-mechanical investigations and advance knowledge of the fracture process, micro-mechanical measurements in the deformation zone are required to determine local stresses and strains. In TPs, craze zones can develop that are important microscopic features around a crack tip governing strength behavior. For certain plastics fracture is preceded by the formation of a craze zone that is a wedge shaped region spanned by oriented micro-fibrils. Methods of craze zone measurements include optical emission spectroscopy, diffraction... 

In reality, several factors were mentioned as being responsible for this behavior, such as variations in bond angle distortion, in the internal stress or in the hydrogen content [40, 76], but all of them are also strongly correlated with the variation of optical gap width in amorphous carbon films. Theoretical work on Raman spectroscopy on DLC materials gave additional support for Dillon s interpretation [77]. 

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