Primary-bonded structure

Today with the advance of structural and high temperature adhesives, aircraft, spacecraft, and missies (109) are built with secondary-bonded and some primary-bonded structures. The PABST (Primary Adhesive Bonding Structures Technology) program (110) was carried out at the Air Force Materials Laboratory between 1976 and 1981. That project led to the construction of a totally adhesive-bonded 42-foot-long circumferential fuselage section of a... 

At the end of the PABST program, there were several questions unanswered about (1) the ease and cost of maintaining the adhesive-bonded structures, (2) the durability in actual service environments where temperature cycles and moisture attack could reduce the life of the bonded joints, and (3) the feasibility and cost of curing an immense primary-bonded structure in an autoclave. 

Wings There are no primary bonded structures in the Airbus wings but there are areas, within the outer wing box and the wing tips, where secondary bonded structures are used. In the A.380 the composite wing ribs are structurally bonded. 

The primary challenge facing adhesive bonding of metals is to obtain sufficient durability of a bonded structure. Initial bond strength in metal-polymer adhesive joints is almost invariably excellent. Challenging the application of adhesives in polymer-polymer joining, however, is the problem of obtaining a joint that is... 

Potter, D.L. et al.. Primary Adhesive Bonded Structure Technology (PABST) Design Handbook for Adhesive Bonding. Report AFFDL-TR-79-3129, Douglas Aircraft Co., Air Force Flight Development Laboratory (FBA), Air Force Systems Command, WPAFB (November, 1979). 

In turn, each M—X bond engages in 3c/4e cu bonds with the opposite L donor of the other r 3-Cp ring. Thus, the following resonance structures summarize the primary bonding pattern, which can be compactly described as two tu bonds ... 

Quantum chemical calculations predict the primary ethylcation, C H/" to have /(-hydrido-bridgcd structure 5 which is 6-8 kcal/mol more stable than the Kekule line-bond structure for the primary cation 4. The ethylcation is not stable enough to be observable directly in superacid media. The NMR chemical shifts were calculated for both isomers 4 and 5 using the GIAO-MP2 method for CCSD optimized structures.23... 

The explanation for the above is twofold. Firstly there is the effect of increasing cavita-tional collapse energy via a lowering in vapour pressure as the temperature is reduced (see above). This does not adequately explain the effect of the change in solvent. The primary process is unlikely to occur inside the cavitation bubbles and a radical pathway should be discarded. The most likely explanation is that the disruption induced by cavitation bubble collapse in the aqueous ethanolic media is able to break the weak intermolecular forces in the solvents. This will alter the solvation of the reactive species present. Significantly the maximum effect is found in 50 % w/w solvent composition - the solvent composition very close to the maximum hydrogen bonded structure. 

Both synthetic and natural polymers have superstructures that influence or dictate the properties of the material. Many of these primary, secondary, tertiary, and quaternary structures are influenced in a similar manner. Thus, the primary structure is a driving force for the secondary structure. Allowed and preferred primary and secondary bondings influence structure. For most natural and synthetic polymers, hydrophobic and hydrophilic domains tend to cluster. Thus, most helical structures will have either a hydrophobic or hydrophilic inner core with the opposite outer core resulting from a balance between secondary and primary bonding factors and steric and bond angle constraints. Nature has used these differences in domain character to create the world around us. 

When secondary Grignard reagents are used, the coupling product sometimes is derived from the corresponding primary alkyl group.169 This transformation can occur by reversible formation of a nickel-alkene complex from the cr-bonded alkyl group. Reformation of the cr-bonded structure will be preferred at the less hindered primary position. 

The isomerization from 10 to 11 in the crystalUne state requires not only the movements of atoms but also a change in the crystal symmetry and the reconstruction of the hydrogen bond network pattern. In the crystals of these primary ammonium carboxylates, ID ladder-type hydrogen bonds are observed. The isomerization from the ZZ to EE form is associated with the rotation of carbonyl groups and the change in the hydrogen bond structure in this case. The quantitative transformation of 10 to 11 in the crystalUne state suggests that the molecular motion in the crystals occurred cooperatively with the minimum movement of atoms in the crystals via a phase transition from the crystal of 10... 

Bonding Agents. These materials are generally only used in wire cable coat compounds. They are basically organic complexes of cobalt and cobalt—boron. In wire coat compounds they are used at very low levels of active cobalt to aid in the copper sulfide complex formation that is the primary adherance structure. The copper sulfide structure builds up at the brass rubber interface through copper in the brass and sulfur from the compound. The dendrites of copper sulfide formed entrap the polymer chains before the compound is vulcanized thus holding the rubber firmly to the wire. 

This structural model has several interrelated parts. Synthetically, we define structure at the primary level. That structure is the bonding between the units that is defined by the synthetic steps. This structure can also be viewed as the topological structure of the molecule. That structural information, however, is insufficient to define or exploit encapsulation. The missing associations are those that link structure at the primary level, structure at the tertiary level (e.g., conformations), and structure relevant to encapsulation (e.g., range of positions of the encapsulated unit with respect to the center and the exterior of the molecule). This latter structural model of encapsulation could then be correlated with encapsulation behaviors. With this information in hand, one might establish the map from molecular design to behavior. 

Metals such as aluminium, steel, and titanium are the primary adherends used for adhesively bonded structure. They are never bonded directly to a polymeric adhesive, however. A protective oxide, either naturally occurring or created on the metal surface either through a chemical etching or anodization technique is provided for corrosion protection. The resultant oxide has a morphology distinct from the bulk and a surface chemistry dependent on the conditions used to form the oxide 39). Studies on various aluminum alloy compositions show that while the oxide composition is invariant with bulk composition, the oxide surface contains chemical species that are characteristic of the base alloy and the anodization bath40 42). 

If the number of primary bonds capable of yielding a particular atom is determined by its valence state (by the number of uncoupled valence electrons corresponding to this st te), then the number of secondary bonds is determined by the valence state of this atom in a molecule and depends upon the structural features of the molecule as a whole and upon external circumstances. 

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