Orientational stresses

X-ray difl raaion (structure grain size preferred orientation stress) Scanning laser microscopy Optical microscopy Oocnl thickness topography nucleation general morphology internal oxidation) l.R. spectroscopy (specialised analysis and applications)... 

Raman spectroscopy is a powerful tool for probing orientation, stress, and strain. Galiotis et al. have written a review on the determination of stress and strain in composites and fibers using Raman spectroscopy [179]. Young et al. discuss the complexities of correct interpretation of molecular orientation information encoded in Raman spectra of polymers [180]. Caution and a suitable number of control studies are necessary to prevent faulty conclusions. 

In PVC siding obtained from coextruded films, warping and curling occurred if films had a mismatch in the orientational stresses. ... 

Temperature, Specimen type Crack location K and orientation Stress ratio C n range, MPa m ... 

Figure 8 shows a typical 0°/90° orientation stress-strain plot. The response is initially linear and is somewhat stiffer than would be expected due to the fibers alone, however it becomes nonlinear at relatively low strain. This behavior is consistent with the matrix contribution to the modulus decreasing with stress due to cracking [39]. The total matrix contribution to load carrying is sufficiently small that a proportional limit can be difficult to... 

Discussion of transient effects in the nucleation kinetics in polymers subjected to orienting stresses bases on a kinetic theory of nucleation proposed in [20-22] for the systems of oriented asymmetric elements. The theory converges to the classical approach in the limit of isotropic orientation. This fact explains apparent validity of the classical theory in the apphcations to unoriented polymers. 

The sheet is softened to an extent such that to stretch, enable, or ease without tearing. The softening behavior purely depends on the thermomechanical behavior in the form of orientation, stress, and crystallinity of the polymeric material. Therefore, the sheet memory is partially removed because of comparatively low temperatures over short periods of time. Polymer with amorphous nature is thermoformed above its glass transition temperature. The forming temperature is slightly above the melting temperature of their crystalline domains. The polymeric sheet is heated by contact, convection, or radiant heater. Then, the heated sheet... 

We will therefore concentrate the discussion on birefringence brought about by orientation stresses. One measure to reduce this is to bring down these stresses as far as possible. From the material suppliers side this has been done by developing a polycarbonate grade especially for optical disc substrate production. This has an improved flowability due to a considerable reduction of the molecular weight, however to such a value that the thermal and mechanical properties still remain acceptable (9). Other necessary modifications have been an improvement of heat stability and optical purity. 

Polymers play a vital part in optical recording media, mainly as the substrate material. Polycarbonate is the material of choice for Compact Disc substrates. However, in particular for magneto-optic rewritable disc substrates it could be attractive to reduce the birefringence not only by optimizing the moulding process, but also by modifying the material towards a lower orientational stress optical coefficient. Work at our laboratories has shown that this can be achieved... 

Two dislocations exert the same, oppositely oriented stress on each other Another stress acts on the first dislocation at the grain boundary, namely the obstacle stress —r created by the grain boundary that causes the pile-up. In equilibrium, forward- and backward-pushing stresses must be the same on each dislocation Tj +T b 0- Summing over all dislocations results in... 

The various parameters like fiber aspect ratio, volume fraction of the libers, its orientation, stress transfer at the interface and liber matrix adhesion influence the properties of natural fiber reinforced composites. The mechanical properties of the composites greatly depend on the influence of various treatments of libers, liber content, and the use of cross-linking agents (Garcia et al. 1995 Vollenberg and Heiken 1989). 

Other factors affecting corrosion include temperature, relative velocities between the metal and the media, surface finish, grain orientation, stresses, and time. 

All PA grades Rapid cooling below Molecular orientations External stresses Cooling stresses Flow-oriented stresses Viscoelastic stress relaxation Residual thermal stresses Anisotropic physical properties Creep and stress relaxation... 

Fiber Orientation Stress Direction Reinforcement Efficiency... 

However, after a certain amount of time warping occurred, which can clearly be traced back to very high internal orientation stresses resulting from excessively slow filling. 

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