Aerospace structures adhesives formulations

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 high-temperature glassy or crystalline transitions of the linear aromatic and heterocyclic polymers were an important drawback for die structural aerospace applications, which need a good flow for the adhesive or composite formulations. 

Epoxy resins are the most versatile product used in aerospace composite hardware. They are employed both alone and in combination with a variety of other resins to form a broad range of products. The only limitation to the number of available products rests in the ability of the formulator to meet the ever-increasing demands for improved structural properties. Greater detail on the use of epoxy resins for bonding can be found in the section on adhesives. 

Despite considerable work over many years, silane pre-treatments or primers prior to structural bonding are still relatively rare in Aerospace applications. Silanes are, though, regularly used as formulating ingredients in Epoxide adhesives (paste and film)... 

We will study the formulation and manufacturing of these films in the relevant chapters. For instance thermosetting structural films based on epoxies are studied in the chapter Epoxy Adhesives in Volume 5, and also in chapter Aerospace Bonding in Volume 1. 

Epoxies have historically been the major adhesive family used for the structural bonding of metals and composites in the aerospace, industrial and automotive industries. They are characterised by curing to hard infusible resins that bond to a wide range of metals and have excellent resistance to heat and the environment. Epoxies have been used since the 1940s and have an excellent track record of successful structural bonding. Two-component and heat-cured one-component versions are available and literally thousands of formulations have been developed over the years for specific applications. 

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