Primary Adhesively Bonded Structures

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). 

Shannon, R. W., et al, Primary Adhesively Bonded Structure Technology (PABST) General Materials Property Data, Douglas Aircraft Co., McDonnell Douglas Corp., Air Force Flight Dynamics Laboratory, Technical Report AFFDL-TR-77-107, September 1977. 

It has often been observed that the application of adhesives to metal fabrication, in common with many other technological innovations, was pioneered by the aircraft industry. It is ironic that this industry, in which safety and reliability command paramount attention, should lead the departure from traditional methods of joining. Today adhesives are used to bond critical parts in commercial and military aircraft and helicopters, spacecraft, rockets, missiles and the US Space Shuttle. The American Primary Adhesively Bonded Structure Technology (PABST) Programme, which ran from 1976-81, was an imaginative attempt to advance significantly the use of bonded... 

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... 

The PABST programme is an imaginatively conceived and typically American attempt to advance significantly the use of bonded stmctures in aircraft. The acronym is derived from Primary Adhesively Bonded Structures Technology and the programme is based on the development of a section, 42 ft long, of a particular transport aircraft... 

Thrall, E. W. (1980) The primary adhesively bonded structure technology (PABST) program. Adhesion 4, AUen, K. W., Ed., Appl. Sci. Publ., London,... 

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). 

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. 

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... 

Structure. Perhaps most interestingly, it was a period of great innovation and experimentation with adhesive bonding of large primary structure for European civil airframe manufacturers and one of relative timidity for manufacturers in the U.S. 

In the aerospace market a distinction is made between primary and secondary structural applications. Joint failure in a primary structure will result in the loss of the aircraft, whereas failure in a secondary structure will result in only localized damage. Structural adhesives are used in both applications. Figure 1.4 illustrates the degree to which adhesive bonding is used in modem aircraft. 

Figure 1.66 Stylized representation of postulated structure of inorganic zinc-rich film in which silicate vehicle is primary valence bonded to zinc atoms on particles of zinc dust pigment. There is no encapsulation, and the film is porous to ingress of electrolyte. This affords good film strength, adhesion, electrical conductivity and cathodic protection...

In the aerospace industry, resinous polymers encompass a wide variety of hardware applications for aircraft, missiles, and space structures. In aircraft, resins are used as a matrix material for primary (flight-dependent) and secondary fiber-reinforced composite (FRC) structures, adhesives for the bonding of metal and composite hardware components, electronic circuit board materials, sealants, and radomes. Missile applications include equipment sections, motor cases, nose cones, cartjon-carbon composites for engine nozzles, adhesive bonding, and electronics. As the exploration of outer space intensifies, applications will become even more exotic. FRC will be used to construct telescopes, antennas, satellites, and eventually housing and other platform structures where special properties such as weight, stiffness, and dimensional stability are important. 

The primary structural role of the face/core interface in sandwich construction is to transfer transverse shear stresses between faces and core. This condition stabilizes the faces against rupture or buckling away ftom the core. It also carries loads normally applied to the panel surface. They resist transverse shear and normal compressive and tensile stress resultants. For the most part, the faces and core that contain all plastics can be connected during a wet lay-up molding or, thereafter, by adhesive bonding. In some special cases, such as in a truss-core pipe. 

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