Crack density analyses

Similar mechanical testing and crack density analyses were performed at each of the three specified freeze-thaw conditioning levels for both unloaded and loaded samples in each of the general conditioning categories, i.e., saturated freeze-thaw (144 samples), saturated constant temperature (144 samples), and dry freeze-thaw (144 samples). 

Ultimate tensile strength, stifihess, and strain-to-failure were determined quasi-statically for each class of as-received material in accordance with ASTM D 3039 Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials using a deflection rate of 2.5 mm/min (0.10 in./min). A total of thirty samples were tested, ten of each material type. In addition, two samples of each material were set aside for crack density analysis using x-ray and optical microscopy techniques. 

There are a number of indicators of fatigue damage that have attracted interest in the literature. During the life of a component subjected to fatigue, the material can exhibit changes in modulus, permanent offset strain, shape of the hysteresis loops, and temperature rise of the specimen surface. Direct evidence of matrix crack density can be obtained by surface replication, while a more detailed analysis of microstructural damage requires scanning electron microscopy (SEM). 

It may be seen from Fig. 3 that, as transverse crack density increases, all stiffness properties of the laminate are significantly reduced. Longitudinal and transverse moduli of the undamaged laminate, calculated from the classical lamination theory, are 166.5 GPa, shear modulus 44 GPa, Poisson s ratio 0.19. When transverse cracking in the 90° layer reaches saturation, the laminate longitudinal and shear moduli are predicted to lose more than 45% of their value. Inclusion of tensile residual stresses into the analysis would lead to even more significant reduction in the longitudinal modulus and Poisson s ratio, but reduction in shear modulus would remain the same. Predictions for a [O/OOi], SiC/CAS laminate are shown in Fig. 4. 

CMC laminates with macrocracks both in the 90° and 0° plies. To capture simultaneous accumulation of damage both in the 90° and the 0° plies, two ECM laminates were analysed simultaneously, as a coupled problem, instead of the original one. Following analysis of stresses in the explicitly damaged layer(s) of ECM laminates, closed form expressions for the reduced stiffness properties of the damaged laminate were derived representing them as functions of crack densities in the 90° and 0° plies. Residual thermal stresses were neglected in the stress analysis, but their value was estimated from the classical lamination theory. 

Recovering the bitumen is not easy, and the deposits are either strip-mined if they are near the surface, or recovered in situ if they are in deeper beds. The bitumen could be extracted by using hot water and steam and adding some alkali to disperse it. The produced bitumen is a very thick material having a density of approximately 1.05 g/cm. It is then subjected to a cracking process to produce distillate fuels and coke. The distillates are hydrotreated to saturate olefinic components. Table 1-8 is a typical analysis of Athabasca bitumen. ... 

Atmospheric gas oil has a relatively lower density and sulfur content than vacuum gas oil produced from the same crude. The aromatic content of gas oils varies appreciably, depending mainly on the crude type and the process to which it has been subjected. For example, the aromatic content is approximately 10% for light gas oil and may reach up to 50% for vacuum and cracked gas oil. Table 2-7 is a typical analysis of atmospheric and vacuum gas oils. ... 

A particular conclusion from this theoretical analysis is that, if a crack has faces that are separated by a thin layer of fluid, so that normal components of traction and displacement are transmitted across the crack but the faces are free with regard to shear components of traction and displacement, then there will be a scattered wave however thin the fluid layer is. This is perhaps not surprising. A Rayleigh wave can exist only because solids can support both longitudinal and shear waves, and the greater part of the displacement in a Rayleigh wave is shear in character ( 6.3). Of course, liquids can support shear stress over a short distance. In a liquid of viscosity r/, and density po, at a frequency o) the amplitude of a shear wave decays by a factor e over a distance... 

In the previous analysis, homogeneous current distribution has been assumed but, on many occasions, corrosion occurs with localized attack, pitting, crevice, stress corrosion cracking, etc., due to heterogeneities at the electrode surface and failure of the passivating films to protect the metal. In these types of corrosion processes with very high local current densities in small areas of attack, anodic and cathodic reactions may occur in different areas of disparate dimensions. 

Figure 8. Experimental evidence of nuclear reactions produced by high-density charge clusters (HDCCs) (a) HDCC strike on a deuterium-loaded palladium foil (b) X-ray analysis of the crack illustrated above, showing new materials produced.

Catalytic activity, assessed by cumene cracking on separated fractions and also by analysis of residual coke on catalyst fractions, shows a sharp decline with increasing density (age). This rapid loss of initial activity coincides with zeolite dealumination which is largely completed as a slow rate of zeolite destruction is established. Subsequent loss of crystallinity has little additional effect on activity. The associated loss of microporosity leads to an apparent increase in skeletal density with increasing age. 

Dealuminated Y zeolites which have been prepared by hydrothermal and chemical treatments show differences in catalytic performance when tested fresh however, these differences disappear after the zeolites have been steamed. The catalytic behavior of fresh and steamed zeolites is directly related to zeolite structural and chemical characteristics. Such characteristics determine the strength and density of acid sites for catalytic cracking. Dealuminated zeolites were characterized using X-ray diffraction, porosimetry, solid-state NMR and elemental analysis. Hexadecane cracking was used as a probe reaction to determine catalytic properties. Cracking activity was found to be proportional to total aluminum content in the zeolite. Product selectivity was dependent on unit cell size, presence of extraframework alumina and spatial distribution of active sites. The results from this study elucidate the role that zeolite structure plays in determining catalytic performance. 

Fig. 2 presents the analysis based on OIT data and the linear extrapolation of these data to longer times. The time to reach depletion of the antioxidant system can thus be predicted even after relatively short testing times (see insert figure in Fig. 2). Data by Hassinen et al. (//) for the antioxidant concentration profiles taken from high-density polyethylene pipes exposed to chlorinated water (3 ppm chlorine) at different temperatures between 25 and 105°C followed the Arrhenius equation with an activation energy of 85 kJ mol (0-0.1 mm beneath inner wall surface) and 80 kJ mol (0.35-0.45 mm beneath the inner wall surface). It is thus possible to make predictions about the time for antioxidant depletion at service temperatures (20-40°C) by extrapolation of high temperature data. However, there is currently not a sufficient set of data to reveal the kinetics of polymer degradation and crack growth that would allow reliable extrapolation to room temperature.

Pyrolysis was carried out on a feed composed of a 50/50 mixture by weight of low-density polyethylene (LDPE) and hydrotreated FT wax. Yields are given in Table 13.2, showing a 385°C- - yield of 57.5 wt%. The yield for a broader lube feed, 343°C- -, was 66.0 wt%. While there was considerable 538°C- - in the feed to the pyrolyzer, there was little 538°C- - in the product, which is believed here to be advantageous for low cloud point. Oleflnicity in the pyrolysis overhead was 76 wt% by PONA analysis. The olefinic overhead liquids from the pyrolysis of both FT wax and LDPE/FT wax were analyzed using gas chromatography. This showed the cracked product to be almost entirely 1-normal olefins and normal paraffins. 

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