Flexible structural bonding

Even stress distribution in the bond line is a fundamental principle of bonding technology. An explanation is given in Fig. 8, where the load bearing capability of rigid, elastic and flexible structural bonding is compared with respect to the bond overlap. The load bearing capability is the area below the curve of the stress level. 

The flexible structural bonding is the combination of rigid and elastic bonding and provides optimised mechanical properties and maximum possible elongation, in combination with structural strength and stiffness. The load transfer of the flexible structural adhesives is lower than that of rigid adhesives and higher than... 

This explains that adhesives suppliers first developed in the seventies the so-called toughened epoxies, flexibilized by addition of a small amount of cross-linkable rubber, and then recently the company SIKA pioneered the so-called flexible structural bonding in which they use PU adhesives derived from their experience in PU sealants, to get semi-structural bonds, for instance, for transportation and automotive or naval uses. 

Fig. 43 shows that a flexible, semi-structural PU adhesive giving only 6 MPa tensile strength may require greater work to break the bond than a high-tensile strength structural epoxy. The reader should refer to the chapters Flexible structural bonding by SIKA, and Epoxy adhesives by 3M, in following volumes of this Handbook. 

For a detailed study of PU adhesives for transportation, automotive, etc., the reader may refer to the chapters Elastic Bonding and Sealing by SIKA in Volume 2 and Flexible Structural Bonding also by SIKA in the next volumes of this Handbook. 

Photodiode arrays have been used as retinal implants [684]. These arrays of p-i-n diodes are fabricated on a thin titanium layer bonded to a glass plate. The total thickness of this flexible structure is 1.5 yum. The microphotodiode array (MPDA) is used to replace photoreceptors (rods and cones) that have become defective due to disease. 

Fluconazole was shown to be crystallizable in the form of a monohydrate and as a 1/4 ethyl acetate solvate, as well as a new nonsolvated form [56], In the hydrate phase the water molecules were established as isolated sites, while the ethyl acetate molecules occupied constricted channels in its phase. In all of the structures, the fluconazole molecule adopted a common overall conformation, but one that was capable of some degree of flexibility. Hydrogen-bonding effects were deduced to be dominant in determining the structure of the different solvatomorphs. 

A very wide range of curing times and temperatures exists for epoxy resin systems. Therefore, they offer a great deal of design flexibility for use both as structural bonding adhesives and protective surface coatings. 

The H-bond belt is incomplete in the aCD molecule, because one glucopyranose unit is in a distorted position. Consequently, instead of the six possible H bonds, only four can be established simultaneously. The yCD is a non-coplanar, more flexible structure therefore, it is the more soluble of the three CDs. 

C-C bond dissociation energies are not the only molecular properties affected by electron transfer. In addition, radical cations exhibit a number of unique characteristics flexible structures [23], a low sensitivity towards steric effects [24], low activation barriers for inter- and intramolecular reactions [25-28], high acidities [29-32] and the inversion of the thermochemical stability order for certain tautomeric systems. Examples in the recent literature demonstrate that it is worthwhile thinking about how the changed molecular properties can be used for the design of new reactions that complement the thermal and photochemical reactivity patterns [26,33-35]. 

Mooij, W.T.M. van Eijck, B.P. Kroon, J. Ab initio crystal structure predictions for flexible hydrogen-bonded molecules. J. Am. Chem. Soc. 2000, 122, 3500-3505. 

Scientists have added to Fischer s idea and suggested that some enzymes are flexible structures. An enzyme might wrap its active site around the substrate as the substrate approaches. Further flexing of the enzyme causes some bonds in the substrate to break and frees the products. Whatever the actual mechanism of an enzyme, its shape is very important to its ability to catalyze a reaction. Because protein function depends so much on the shape of the protein, changing a protein s shape can inactivate a protein. 

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