Incompatible interfaces

While the overall development used a Windows application programming interface, incompatibilities exist across platforms (Microsoft Windows, Apple OS X). For this reason, we opted to use a more standardized interface using HTML that would be more accessible, at the cost of a few features (pairing text to certain times in the videos and full-screen video). Aside from these two features, the HTML interface is identical to the enhanced interface, using the same color scheme and layout and containing the same content. 

The analysis is used to identify hazards due to interface incompatibilities. 

It should be emphasized at this point that the basic requirements of compatibility and consistency of finite elements used in the discretization of the domain in a field problem cannot be arbitrarily violated. Therefore, application of the previously described classes of computational grids requires systematic data transfomiation procedures across interfaces involving discontinuity or overlapping. For example, by the use of specially designed mortar elements necessary communication between incompatible sections of a finite element grid can be established (Maday et ah, 1989). 

Eabrication techniques must take into account the metallurgical properties of the metals to be joined and the possibiUty of undesirable diffusion at the interface during hot forming, heat treating, and welding. Compatible alloys, ie, those that do not form intermetaUic compounds upon alloying, eg, nickel and nickel alloys (qv), copper and copper alloys (qv), and stainless steel alloys clad to steel, may be treated by the traditional techniques developed for clads produced by other processes. On the other hand, incompatible combinations, eg, titanium, zirconium, or aluminum to steel, require special techniques designed to limit the production at the interface of undesirable intermetaUics which would jeopardize bond ductihty. 

Transition Joints. Use of explosion-clad transition joints avoids the limitations involved in joining two incompatible materials by bolting or riveting. Many transition joints can be cut from a single large-area flat-plate clad and deflvered to limit the temperature at the bond interface so as to avoid undesirable diffusion. Conventional welding practices may be used for both similar metal welds. 

Most polymer pairs are thermodynamically incompatible, in the sense that their free energy of mixing is positive. This does not mean that there is absolutely no interdiffusion at all at the interface between them adjacent to the interface limited interdiffusion occurs, which can be seen as an increasing of the low surface entropy implied by a smooth surface [30-33]. This nanoscale roughening of an interface can increase the adhesion between the polymers. 

More extensive roughening of an interface between incompatible polymers can be obtained by use of various types of copolymer, introduced at the interface as putative compatibilisers. The interface may be strengthened, as a result of interdiffusion and roughening on a nanoscale. Many elegant experiments have been done in this area. 

These effects have been found by Creton et al. [79] who laminated sheets of incompatible polymers, PMMA and PPO, and studied the adhesion using a double cantilever beam test to evaluate fracture toughness Fc. For the original laminate Fc was only 2 J/m, but when interface reinforced with increasing amounts of a symmetrical P.M.M.A.-P.S. diblock copolymer of high degree of polymerisation (A > A e), the fracture toughness increased to around 170 J/m, and then fell to a steady value of 70 J/m (Fig. 9). 

Fig. 10. Schematic representation of a random copolymer at the interface between two incompatible homopolymers. Incompatibility increases in the order (a), (b), (e).

Toughening of a polymer-polymer interface with random copolymers can sometimes be more effective than with diblocks, providing the polymers are not too incompatible [80]. This is of industrial, as well as of scientific, interest as random copolymers are usually cheaper to produce. 

The randomization stage refers to the equilibration of the nonequilibrium conformations of the chains near the surfaces and in the case of crack healing and processing, the restoration of the molecular weight distribution and random orientation of chain segments near the interface. The conformational relaxation is of particular importance in the strength development at incompatible interfaces and affects molecular connectivity at polymer-solid interfaces. 

This solution assumes that the beams behave elastically and that all the energy dissipation is associated with the pullout process. Typically for rigid incompatible interfaces, this fracture energy is quite low, ca. 1-5 J/m [1,20,21,61,59]. 

Consider the incompatible A/B polymer interface shown in Fig. 16. In the absence of compatibilizers, the interface is very weak such that the strength can be described by the nail solution as [11... 

Fig. 16. A/B incompatible interface of width X, with E di-block compatibilizers of length L.

By placing diblocks or random copolymers of aerial density X, at incompatible interfaces (Fig. 16), following the work of Creton, Brown and Kramer et al. [59,60,81-83], the percolation model predicts that XL... 

A WBL can also be formed within the silicone phase but near the surface and caused by insufficiently crosslinked adhesive. This may result from an interference of the cure chemistry by species on the surface of substrate. An example where incompatibility between the substrate and the cure system can exist is the moisture cure condensation system. Acetic acid is released during the cure, and for substrates like concrete, the acid may form water-soluble salts at the interface. These salts create a weak boundary layer that will induce failure on exposure to rain. The CDT of polyolefins illustrates the direct effect of surface pretreatment and subsequent formation of a WBL by degradation of the polymer surface [72,73]. 

Characterization and control of interfaces in the incompatible polymer blends were reported by Fayt et al. [23]. They used techniques such as electron microscopy, thermal transition analysis, and nonradiative energy transfer (NRET), etc. They have illustrated the exciting potentialities offered by diblock copolymers in high-performance polymer blends. 

Due to the smallness of the entropy of mixing, most polymer mixtures are at least partially incompatible, and blends contain A-rich and B-rich domains, separated by interfaces. The intrinsic width of these interfaces is rather broad (it varies from w = aJin... 

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