Micro structure variations

This paper presents results from a study of assemblies composed of glass fibre reinforced epoxy composites. First, tests performed to produce mixed mode fracture envelopes are presented. Then results from tests on lap shear and L-stiffener specimens are given. These enabled failure mechanisms to be examined in more detail using an image analysis technique to quantify local strain fields. Finally the application of a fracture-mechanics-based analysis to predict the failure loads of top-hat stiffeners with and without implanted bond-line defects is described. Correlation between test results and predictions is reasonable, but special attention is needed to account for size effects and micro-structural variations induced by the assembly process. 

A critical analysis of Table 6.2 indicates micro-structural variations in the fly ash and its significantly zeolitized residues (SZR), which can be addressed in terms of different characteristics of the crystallites (viz., size (C5), d-spacing of atomic planes, full width at half maximum, FWHM (jS), and the h, k, I values of the atomic planes, refer Table 6.2). Incidentally, residues 1.5-R2-24 exhibit less d-spacing (=1.37 A, corresponding to planar alignment 910 as compared to 220), which corresponds to close atomic packing as compared to other residues. 

Lu B, Zheng Y, Scriven LE, Davis HT, Talmon Y, Zakin JL (1998) Effect of variation counterion-to-surfactant ratio on rheology and micro-structures of drag reducing cationic surfactant systems. Rheol Acta 37 528-548... 

Figure 7.2 Variation of environmental impact potentials as a consequence of the change from macro-scaled batch (0%) to micro-reaction mode Vbatch = 60%, Vdonti = 88% four scenarios regarding the lifetime of the micro-structured devices (Conti wc 1 week, Conti Set 3 months, Conti Sc2 3 years, Conti Sc3 10 years).

Application. Micro- and nanobeam optics are used to demagnify the cross-section of the primary beam. By means of the respective setups structure variation in inhomogeneous materials can be studied with micrometer or nanometer size resolution, respectively. For this purpose the sample is moved through the beam while... 

Anthraquinones are found extensively in various plant species, especially from the families Liliaceae, Polygonaceae, Rhamnaceae, Rubiaceae and Fabaceae. They are also biosynthesized in micro-organisms, e.g. Penicillium and Aspergillus species. The following structural variations within anthra-quinone aglycones are most common in nature. 

Third, there may be a concentration gradient of reactants and products along the length of the catalyst bed. If the structure of the catalyst depends upon the composition of the gas phase, then an average of the various structures will be measured. There is little discussion of this topic in the literature of XAFS spectroscopy of working catalysts. An extreme example of structural variations within a sample is discussed in Section 6, where there is a discussion of XAFS spatially resolved spectra recorded to allow direct observation of the axial distribution of phases present. If the XAFS data are not measured with spatial resolution, then it is recommended that XAFS data be measured under differential conversion conditions. However, if the aim of the experiment is to relate the catalyst structure directly to that in some industrial catalytic processes, then differential conversion conditions will only reflect the structure of the catalyst at the inlet of the bed. To learn about the structure of the catalyst near the outlet of the bed, the reaction has to be conducted at high conversions. If it is anticipated that this operation will lead to variations in the catalyst structure along the bed, then the feed to the micro-reactor should be one that mimics the concentration of reactants toward the downstream end of the bed (i.e., products should be added to the reactants). 

Processing conditions required to attain desirable composite properties can be defined more easily if the factors controlling composite microstructure are understood. Such factors include type of precursors employed and the composite s processing history. The microstructure of the matrix may contribute to the performance of the fibers and influence the properties of the composite. Reviewed are experiments to determine matrix micro-structural features, how microstructural variations are achieved, and ways in which thermal expansion and fracture behavior relate to microstructure. 

The wide array of 16-membered macrolides has amply supplied chemists with starting materials for structural modifications, and the extensive structural variations have provided a wealth of ideas from which hybrid molecules have been conceived. In addition to synthesis by purely chemical means, structural modifications have been effected by bioconversions, alterations of biosynthetic pathways, and genetic manipulations of macrolide-producing micro-organisms [13]. These natural structural variations have also contributed to a better understanding of structure-activity relationships and have been used to successfully guide synthetic programmes. Finally, these complex natural products have inspired numerous... 

Marine water nutrients concentration is responsible for phytoplankton structure variation. Therefore, the quantities of organic substance (Table 1) in 2001 and 2002 have triggered growth of non-diatom species, given that most of micro-algal consumers of organic substance are mixotrophic species of microalgae, which predominated in the respective time span. 

The chemical reactions involved in the decomposition of limestone are deceptively simple. There are, however, complications, particularly with dolomite, which are believed to be caused by variations in crystallography and micro-structure. 

Hallberg E, Johansson KUI, Elofsson R (1992) The aesthetasc concept structural variations of putative olfactory receptor cell complexes in Crustacea. Micros Res Tech 22 325-335... 

The above discussion considered cracks from a macroscopic viewpoint but even for a pure mode I loaded crack, cracks are often deflected at a micro-structural level. This crack deflection is a result of variations in the fracture toughness within real materials and the influence of localized stress fields. These observations imply that mixed mode effects can play a role even in a failure that appears to be a result of pure mode I loading, i.e., with the crack propagating normal to the maximum stress. Crack deflection on the microstructural scale are discussed further in the next section. 

Invariably the fractional n values are close to 2 and this has been attributed to the growth of rods whose numbers are increasing with time and inherent in the structure of spherulites. Calvert et al. using a u.v. optical microscope, have obtained some evidence from the variation in amorphous content within spherulites of the complexity of the micro-structure of spherulites. The central regions of the spherulites contained less amorphous-regions than the outer, and... 

A numerical model accounts for the variation in liquid film thickness and back mixing effects. It can be used for a wide range of process conditions in micro-structured falling-film contactors. It enables also investigation of physical and chemical absorption systems with slower reaction kinetics, in which the mass-transfer resistance is concentrated in the liquid phase [143]. 

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