Durability of Adhesively Bonded Structures

Intensive testing of epoxy aerospace adhesives on aluminium [14] has shown that, from an environmental point of view  

Adhesives become weak and ductile at high temperatures and brittle at low temperatures. 

The yield stress and modulus of all adhesives decrease with increasing temperature and humidity. 

The plastic behaviour of adhesives at elevated temperatures causes significant shear deformation. 

The mechanical properties of adhesives can be substantially degraded by the absorption of moisture. 

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Bascom, W.D., Cottington, R.L. and Timmons, C.O. Durability of Adhesive Bonded Structures (Ed. Bodnar, M.J.), Journal of Applied Polymer Science, Applied Polymer Symposia 32, J. Wiley and Sons, New York, 1977, p. 165. 

Minford, J.D., Comparison of aluminum adhesive joint durability as influenced by etching and anodizing treatments of bonded surfaces. Journal of Applied Polymer Science, Applied Polymer Symposia, 32 91-103, 1977, based on symposium on Durability of Adhesive Bonded Structures held at Picatinny Arsenal, October 27-29,1976. 

The major concerns over the use of adhesives, however, are that no quick and easy inspection methods are available to verify the integrity of the adhesive joints and that the performance of adhesive joints may degrade on exposure to hostile environments. A certain amount of degradation in performance is no cause for concern, provided that it is predictable and can be allowed for in the design specifications of the adhesive joint. This and other aspects of the durability of adhesively bonded structures will be discussed in Chapter 8. 

J. L. Rose, Aspects of the adhesive bond strength classification problem, in Durability of Adhesive Bonded Structures, pp. 389-398, Proc. Applied Polymer Symposium 32, Pitcatinny Arsenal, NJ (October 27-29, 1976). 

Murray BD. Anaerobic Adhesive Technology. Preprint Booklet, Symposium on Durability of Adhesive Bonded Structures, Sponsored by U.S. Army Research and Development Command. Dover, NY Picatinny Arsenal 1976 599—610. [Also published in JAppl Polym Sci Appl Polym Symp. 1977 32 411-420.]... 

Wegman RE. Durabihty of some newer structural adhesives. J Appl Polym Sci, Appl Polym Symp 1977 32 1-10, based on Symposium on Durability of Adhesive Bonded Structures held at Picatinny Arsenal October 27—29, 1976. 

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... 

Adhesives and sealers can be an important part of a total corrosion protection system. Structural bonding procedures and adhesives for aluminum, polymer composites, and titanium are well established in the aerospace industry. Structural bonding of steel is gaining increasing prominence in the appliance and automotive industries. The durability of adhesive bonds has been discussed by a number of authors (see, e.g., 85). The effects of aggressive environments on adhesive bonds are of particular concern. Minford ( ) has presented a comparative evaluation of aluminum joints in salt water exposure Smith ( ) has discussed steel-epoxy bond endurance under hydrothermal stress Drain et al. (8 ) and Dodiuk et al. (8 ) have presented results on the effects of water on performance of various adhesive/substrate combinations. In this volume, the durability of adhesive bonds in the presence of water and in corrosive environments is discussed by Matienzo et al., Gosselin, and Holubka et al. The effects of aggressive environments on adhesively bonded steel structures have a number of features in common with their effects on coated steel, but the mechanical requirements placed on adhesive bonds add an additional level of complication. 

Although numerous studies (1-3) have described work aimed at establishing criteria for the durability of adhesive joints, a thorough understanding of effects of the chemical and mechanical properties, on the durability of adhesive bonds is lacking. More specifically, the effects of surface preparation and dynamic loading, especially under environmental service conditions, has not been explored in detail for automotive structures. In this paper, a description of the effects of environment on the durability of adhesive bonds is presented. Particular attention is given to... 

The environmental durability of adhesively-bonded aluminum structures is of prime importance in the aircraft industry. 

H Hamada, Z Maekawa, T Morii, A Gotoh and T Tanimoto, Durability of adhesive bonded FRP joints immersed in hot water . Durability of Polymer-based Composite Systems for Structural Applications, eds A H Cardon and G Verchery, London, Elsevier Applied Science, 1991, p 418. 

The sustained load that is applied to the bond in relation to the bonds control strength is certainly a critical parameter. Whether or not the load has any effect on the adhesive itself (analogous to stress corrosion cracking of metals) cannot be ascertained from our data. The literature, especially that of Bascom (19) would indicate that it does. This work does indicate that designers of adhesively bonded structure should take durability testing of this sort into account in their design exper imentation. 

Although the environmental resistance of the adhesive does affect the durability of a bonded structure, experience has shown that it is seldom the dominant factor. Of greater importance is the nature of the adhes-ive/adherend interface and the surface treatment of the adherends. The effect of the nature of the adhesive is thus primarily related to how this influences the environmental stability of the interfacial region. ... 

J. D. Minford, Durability evaluation of adhesive bonded structures, in Adhesive Bonding (L. H. Lee, ed.). Chapter 9, Plenum Press, New York (1991). 

Hamada H, Maekawa Z, Morii T, Gotoh A, Tanimoto T (1991) Durability of adhesive bonded FRP joints immersed in hot water (chap. 46). In Cardon AH, Verchery G (eds) Durability of polymer based composite systems for structural applications. Elsevier, Amsterdam, pp... 

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