Durability of bond

Extensive information on the outdoor durability of bonded aluminum joints is available in the reviews of Minford.61,62,63 Hartshorn has also provided a catalog of references to outdoor weathering of structural adhesives by adhesive class and exposure conditions.64... 

The data discussed above show that the tensile strength of sulfur-wood bonds exceeds that of whole wood. The durability of bonds depends on a combination of factors, especially elasticity. Some 12 standard modified sulfur samples are now eight years old and have retained their strength. 

Figure 19-21. Effect of temperature and load on the durability of bonded MoS2-graphite films. Data by Stupp and Wright with the Hohman tester...

TABLE 19-18. EFFECT OF TEMPERATURE ON THE DURABILITY OF BONDED FILMS OF SOLID LUBRICANTS... 

TABLE 19-19. EFFECTS OF TEMPERATURE AND VACUUM ON THE DURABILITY OF BONDED MoS2/PbS FILMS... 

Figure 19-22. Effect of temperature on the durability of bonded solid lubricant films. Data by Campbell and Hopkins [106] with the Hohman tester at 73.15 cm/s, 2158 N load. The curves are identified in the text.

The work of Fusaro [108, 111, 118, 126], demonstrates that there is a distinction between the macroscopic durability of bonded multicomponent films, as shown by profilometric measurements for instance, and the dura-... 

The experimental program was conducted to determine the effects of freeze-thaw cycling on the durability of bond between bonding materials and concrete. 

The results of steel pull out tests show that the RPC not only enhances steel bond strength but also helps to increase bond durability. The strength and durability of bond of RPC to steel are much better than those of RC and HSM specimens subjected to the same environmental conditions. 

From the above discussion, it follows that it should be possible to improve the durability of bonded joints by the introduction of suitable coupling agents at the interface. If the coupling agent is capable of chemically interacting with the metal or its oxide, displacement of the adhesive at the interface will be prevented. 

The effects of water and temperature on the adhesive itself are also of utmost importance to the durability of bonded structures. In the presence of moisture, the adhesive can be affected in a number of ways, depending on its chemistry and how rapidly the water permeates through and causes significant property changes [51,86-88]. The potential efficacy of moisture penetration on the locus of failure of bonded joints has been discussed in the previous section. As expected, elevated temperature conditions tend to degrade joint strength at a faster rate. 

In summary, bonded repairs are the preferred approach for manufacturing repairs to both honeycomb sandwich and monolithic secondary stmcture. However, for the FAA and European Airworthiness and Safety Administration, the main reason for withholding certification of bonded repairs for primary structure is the lack of certainty over bond quality as it is not possible to assess strength and durability of bonded joints without destructive testing. 

This article discusses briefly the use of adhesives on the construction site in the context of structural repair and reinforcement the requirements and practical dilficulties in the work on site with regtirds to the strength and durability of the rehabilitated timber structure and the consequent need for queility control. It also highlights the characteristics and requirements that must be fidfilled by structural adhesives and reinforcing materials factors affecting performance and durability of bonded joints tmd ways to improve adhesion and durability. Finally, it points out some research needs and future developments identified by the authors. 

A matter of much practical importance is the durability of bond strength when joints are exposed to aggressive environments. A cursory examination of this point was carried out as follows joints of PVC/PU and ABS/PU were prepared by cure procedure C2. Several of these were aged at 50 °C/50% relative humidity for up to 10 days and lap-... 

Due regard should be paid to the practical difficulties of achieving a high standard of substrate surface pretreatment in repair and strengthening works on site. The stability of the adherend/adhesive interface is probably the most important factor in the durability of bonded joints. 

Surface preparation is also very important for long term durability of bonded joints. Laek of proper surface preparation of substrates prior to adhesive bonding ean attribute to surface contamination which leads to adhesive failure. 

Extensive information on the durability of bonded aluminum joints is available in the reviews of Minford. " Figure 4 illustrates some typical results, showing the effect of adhesive variation on joint durability for a marine exposure. Vinyl-phenolics and nitrile-phenolics have an excellent history of joint durability and rank among the most resistant to environmental deterioration. In spite of this, however, the current trend is to use epoxy-based adhesives, which provide easier processing and higher peel... 

This section focuses very briefly on the most relevant of the aforementioned factors, thus providing only a general understanding of the factors that influence the durability of bonded timber and concrete joints. The durability of APC materials has already been discussed in the previous chapters so is not dealt with here. The durability of the substrates, timber and concrete, is not also dealt with here the reader can obtain information on this topic from the relevant sub-section of Section 22.6. 

EN 15190 Structural adhesives. Test methods for assessing long-term durability of bonded metallic structures. 

EN 14444 Structural adhesives. Qualitative assessment of durability of bonded assemblies. Wedge rupture test. 

Frihart, C. R. (2009). Adhesive groups and how they relate to the durability of bonded wood. Journal of Adhesion Science and Technology, 23, 601-617. 

The chemical attributes of adhesion cover a much more subtle and wider range of interactions described as primary or secondary bridging. Primary bridging can result from direct chemical reaction between the adhesive and adherend, while secondary bridging relates to the residual electrical forces which surround the respective molecules. It is assumed that these fundamental energy relationships and their association with the wetting phenomena have been covered in the earlier chapters of this book. It should suffice to state that better wetting of the adherend by the adhesive correlates directly with superior durability of bonded structures in the actual service environments. 

The reader should bear in mind that the American Society for Testing and Materials (ASTM) has developed a number of standardized testing procedures which can be used for evaluating the long-term durability of bonded wooden structures. A partial listing of some of these can be found among the list of references at the end of this chapter. ( 2-86)... 

TEST ENVIRONMENTS FOR DETERMINING THE DURABILITY OF BONDED STRUCTURES... 

J. D. Minford, Durability of bonded aluminum structure, SAMPE J. 11, (July-Sept. 1975). 

A. W. Bethune, Durability of bonded aluminum structure, 19th Natl. SAMPE Symp., Los Angeles, Calif. (April 1974). 

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