Aerospace structures adhesives commercial

The aerospace field is a broad one and has a complex history. A comprehensive review of structural adhesive applications on currently flying aerospace vehicles alone could fill its own book. Hence this chapter will concentrate on the aerospace commercial transport industry and its use of adhesives in structural applications, both metallic and composite. Both primary structure, that is structure which carries primary flight loads and failure of which could result in loss of vehicle, and secondary structure will be considered. Structural adhesives use and practice in the military aircraft and launch vehicle/spacecraft fields as well as non-structural adhesives used on commercial aircraft will be touched on briefly as well. 

Epoxy adhesives have become the most recognizable structural adhesive type. They have found commercial success in demanding industries such as aerospace, automotive, building and construction, and electrical and electronic. Their ease of use has also encouraged their commercialization in the do-it-yourself markets, which has added to the exemplary reputation of epoxy adhesives. 

Commercial applications for epoxy resins systems were at one time predominantly, indeed almost exclusively, held by the structural adhesives industry. These systems operate as some of the best available coatings in automotive and aerospace industries. 

The third section devotes itself to an in-depth examination of the structural bonded joint the substrates, primers and the structural adhesives themselves. In this last area, a full appraisal is made of a typical range of commercially available structural adhesives. This examines their role in the bonded structure, the formats in which they are supplied, the basic chemistries employed with their relative cure cycles and generic formulations. This is augmented with key properties of selected adhesives from this range and a typical qualification package generated for one adhesive to meet typical aerospace specifications. The section concludes with brief outlines as to how the adhesives are made, how they are applied to the substrates to be bonded and file methods by which they can be cnred. 

The tables and text below show the makeup of a typical range of commercially available structural adhesives (Redux from Hexcel Composites " ) and their supporting primers, syntactic pastes, and foaming adhesives. The whole range is considerably larger—to meet the demands of other industries such as road and marine transport, electrical, and electronics, and so on—but here only the key products for the aerospace market are shown. Table... 

Mechanical attachment of components, devices, and other parts of an electronic assembly is the prime function of adhesives. Although adhesives are expected to bond a wide variety of materials for electronic applications, they do not need to be structural. They should, however, meet minimum tensile and shear strengths in order to withstand mechanical shock, thermal shock, thermal cycling, and vibration as specified for the intended application. For consumer and commercial products, these stresses may be minimal. For high reliability aerospace and medical systems, more severe tests as defined in MIL-STD-883 and other documents must be used. 

Aromatic polybenzimidazoles were synthesized by H. Vogel and C. S. Marvel in 1951 with anticipation, later justified, that the polymers would have exceptional thermal and oxidative stability. Subsequently, NASA and the Air Force Materials Laboratory (AFML) sponsored considerable work with polybenzimidazoles for aerospace and defense applications as a non-flammable and thermally stable textile fiber and as high temperature matrix resins, adhesives and foams. The route to fiber used solutions of high molecular weight polymer. Structural applications used low temperature melting pre-polymers that were cured (polymerized) in place. Applications of polybenzimidazoles were not implemented in the 60 s and 70 s since the polymers tetraamine precursors were not commercially available. 

Adhesives are used extensively by the aerospace industry for bonding structural components of aircraft (both military and commercial), missiles, and satellites. Sealants are used in joints around windows, in fuel tanks, etc. hot melts and pressure sensitive adhesives are utilized in aircraft interiors (primarily in fabricating decorative panels) while thermosetting adhesives are used to bond load bearing structural components. 

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